•
IN VES
DENVER. COLORADO
DECEMBER 1979
-------
-------
Environmental Protection Agency
Office of Enforcement
EPA-330/1-79-003
THE USE OF LIDAR FOR EMISSIONS
SOURCE OPACITY DETERMINATIONS
Arthur W. Dybdahl
Chief, Remote Sensing Section
December 1979
National Enforcement Investigations Center
Denver, Colorado
-------
CONTENTS
I INTRODUCTION. . . . . . .
. .. . . . . .
. . . . . ..
.. .. .. .. ..
II SUMMARY AND CONCLUSIONS
.. .. .. .. .. ..
.. .. .. .. .. .. ..
.. .. .. .. .. ..
III BACKGROUND OF THE LIDAR . . .
.. .. .. .. ..
.. .. .. .. ..
.. .. .. .. .. ..
IV THE BASIC CONCEPT OF LIDAR . . . .
.. .. .. .. .. .. .. ..
.. .. .. .. .. ..
V DESCRIPTION OF THE EPA/NEIC OMEGA-1 LIDAR SYSTEM. .
.. .. .. .. ..
VI PERFORMANCE EVALUATION AND THE CALIBRATION MECHANISM
OF THE OMEGA-1 LIDAR . . . . . . . . . . . . . . . . . . . .
AERQSOL CHAMBER TESTS. . . . . . . . . . . . . . . . . . .
INTERNAL CALIBRATION MECHANISM FOR THE OMEGA-l LIDAR . . . .
CORRECTIVE ACTION PERFORMED ON THE OMEGA-l LIDAR . . . . . .
VII LIDAR SAFETY IN THE ENVIRONMENT. . . . . .
. . . . . 113
. . 119
.. .. .. ..
VIII USE OF THE OMEGA-l LIDAR IN EPA ENFORCEMENT. .
REFERENCES. .
.. .. .. .. ..
.. .. .. ..
.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
APPENDIX
TABLES
V-I Model 624 Laser Characteristics. . . . . . . . . . . . . . .
V-2 Mobile Lidar Receiver Characteristics. . . . . . . . . . . .
V-3 Optical Density vs Optical Transmittance. . . . . . . . . . .
V-4 Logarithmic Channel Constants. . . . . . . . . . . . . . . .
VI-1 Data Samples. .- . . . . . . . . . . . . . . . . . . . . . . . 83
VI-2 Optical Generator Evaluation Test Results. . . . . . . . . . 91
VI-3 Linear Channel Evaluation Test Results. . . . . . . . . . . . 95
VI-4 Logarithmic Channel Evaluation Test Results. . . . . . . . . 98
VI-5 Lidar vs Smoke Generator Opacity Test Result Summary. . ... . 102
1
4
11
14
24
70
72
85
92
. . 144
26
27
39
57
-------
IV-I
IV-2
IV-3
IV-4
IV-5
V-I
V-2
V-3
V-4
V-5
V-6
V-7
V-8
V-9
V-IO
V-11
V-12
V-13
V-14
V-15
V-16
V-17
V-18
V-19
V-20
V-2l
V-22
V-23
V-24
V-25
V-26
VI-l
VI-2
VI-3
VI-4
VI-5
VI-6
VI-7
VI-8
VI-9
VI-I0
VI-ll
VI-12
VI-13
VI-14
VI -15
V I -16
VI-17
VI-18
VI-19
VI-20
VlII-l
VIII-2
VIII-3
VI II-4
VI II - 5
VII 1-6
VI II-7
VIII-8
VIII-9
VIII-I0
FIGURES
Typical Lidar Field Set-up. . . . . . . . . . . . . . . . . . . . . . . . .
Oscilloscope Presentation, Signal Amplitude vs Range. . . . . . . . .
Li dar Transmi tter - Recei ver Convergence. . . . . . . . . . . . . . .
Lidar Opacity Measurement Mechanism. . . . . . . . . . . . . . . . . . . . . . . .
Oscilloscope Presentation Signal Amplitude vs Range. . . . . . . . . . . . . . . . . . . .
Schematic Diagram of the Omega-l Lidar System . . . . . . . . . . . .
Linear Channel Video Signal for Clear Air. . . . . . . . . . . . . . . . . . . . . . . . .
Linear Channel Video Signal, 20% Opacity. . . . . . . . . . . . . . . . . . .
Logarithmic Channel Video Signal, 85% Opacity, Uncorrected for I/R2 . . . . . . . .
Logarithmi c Channe 1 Vi deo Signa 1, 85% Opac i ty, Corrected for I/R2 . . . . . . . . . .
Plume Opacity vs Logarithmic Channel Signal Drop. . . . . . . . . .
Logarithmic and Linear Channels: One-bit Resultant Error as a Function of Opacity.
Linear Channel Video Signal 80% Opacity, Uncorreted for 1/R2 . . . . .
Linear Channel Video Signal 80% Opacity, Corrected for I/R2 . . . . .
Suppressed Plume Spike, Linear Channel Video Signal, 20% Opacity. . . . . . .
Suppressed Plume Spike and Near-Region Signal. . . . . .
Sketches of Lidar A-Scope 8ackscatter Signals . . . . .
1/R2 Correction Mechanism. . . . . . . . . . . . . . . . . . .
Computer Plots of Lidar A-Scope Backscatter Signals. . . . . .
Examples of Pick Intervals - Reference Signals. . . . . . . .
Examples of Pick Intervals - Plume data Signals. . . . .
Examples of Pick Intervals - Plume Data Signals. . . . . . . . . . . . . . . . . .
Examples of Pick ,Intervals - Plume Data Signals . . . . . . .
Examples of Pick Intervals - Plume Data Signals. . . . . . . . . . . . . . . . . . . . . .
Examples of Pick Intervals - Plume Data Signals. . . . . . . . . . . . . . . . . .
Diagram Showing Digital Data Flow Within Omega-l Lidar System
Two-dimensional Plot of Omega-l Lidar Opacity Data. . . . . . . . . . . . . . . . . . . . .
Omega-l Mobile Lidar System: View of Right Side. . . . . . . .
Omega-l Mobile Lidar System: View of Left Side
Omega-l Lidar: Generator Room. . . . . . . . . . . . .
Omega-l Lidar: Rear View. . . . . . . . . . . . . . . . . . . ',' .
. . . . . . . .
. . . . . .
. . . . . .
. . . . .
Diagram of Experimental System. . . . . . . . . . . . . . . . . . . . . . . . . . .
Aerosol Chamber Details. . . . . . . . . . . . . . . . . . . . . . . .
SRI International Aerosol Test Chamber Facility . . . . . . .
Lidar-Derived Opacity Values Plotted Against Corresponding Transmissometer-Observed
Opacity Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Frequency Distribution and Best-Fit Normal Distribution for the Difference in Lidar
and Transmissometer-Measured Opacities . . . . . . . . . . . .
Lidar Optical Pulse Generator. . . . . . . . . . . . . . . . . . . . . . . . .
Block Diagram: Optical Test Signal Generator 29 . . . . . . .
Light Sources and Optical Components29 . . . . . . . . . . . . . . . . . . . . . . .
Lidar Atmospheric Backscatter Signal, Uncorrected for 1/R2 . . . . . .
L idar Atmospheric Backscatter Signal, Corrected for I/R2 . . . . . . .
Lidar Receiver Time Cycle. . . . . . . . . . . . . . . . . .
Omega-l Lidar: Photomultiplier Tube (pm) Linearity. . . . . .
Lidar - Smoke Generator Tests: 10% Average Opacity. . . . . . . . . .
Lidar - Smoke Generator Tests: 11% Average Opacity
Lidar - Smoke Generator Tests: 20% Average Opacity
Lidar - Smoke Generator Tests: 31% Average Opacity. . . . . . . . . .
Lidar - Smoke Generator Tests: 45% Average Opacity
Lidar - Smoke Generator Tests: 55% Average Opacity. . . . . . . . . .
Opacity ~1easurement Compari son: Lidar, In-Stack Transmi ssometer, VEO's . .
Opacity Measurement Comparison: Lidar, In-stack Transmissometer, VEO's .
. . . . . . .
82
86
87
88
90
. . . . . .. 90
. . . . . . . . 93
96
. . . . . . . . . . . 103
. . . . . . . 104
. . . . . . . . . . . 105
. . . . . . . 106
. . . . . . . . . . . 107
. . . . . . . 108
. . . . . 110
. . . 112
Range Calculation for Plume Measurement Position. . . . . . . . . . . . . . . . . . . 123
Pictoral Diagram of the Running Average . . . . . . . . . . . . . . . . . . . 126
Cycl ic Process. . . . . . . . . . . . .'. . . . . . . . . . . . . . . . . . . . 127
Elevation Angle Compensation for Vertical Plumes . . . . . . . . . . . . . . . 133
Laser Beam Inclination Angle Correction Requirement. . . . . . . . . . . . . . . . . . . . 135
Correction in Opacity for Drift, Residual Region of Attached Plume. . . . . . . . . . 137
Cover of Lidar Log Book. . . . . . . . . . . . . . . . . . . 139
Lidar Log Control Number Tabulation . . . . . . . . . . . . . . 140
Li da r Log 0 f Opel'at ions - Sheet 1 . . . . . . . . . . . . . . . . . . . . . . . . . 142
Lidar Log of Operations - Sheet 2 . . . . . . . . . . . . . . . 143
15
16
17
21
22
25
29
30
33
33
35
36
38
38
40
40
44
46
47
49
50
51
52
53
54
59
63
65
66
67
69
73
75
77
81
-------
1.
INTRODUCTION
The National Enforcement Investigations Center, Office ,of Enforcement
of the U.S. Environmental Protection Agency (EPA-NEIC) is proposing a new
alternate method [see Appendix] for the remote quantitative measurement of
the opacity of stationary source visible emissions. This method is equally
applicable to opacity measurements conducted in either day- or nighttime
lighting conditions with significantly greater accuracy than available with
Reference Method 9.
The quantitative opacity measurements are made with a mobile lidar*
(laser radar) system. The lidar mechanism is applicable to measuring smoke
plume opacity at numerous wavelengths of laser radiation in the visible and
infrared regions of the optical spectrum. However this report is solely
addressed to a mobile lidar which uses a ruby (solid state) laser as a trans-
mitter. Its laser radiation is deep red, the wavelength of which is 6943
Angstroms.
The ruby laser was chosen for the following reasons:
The red light (A = 6943 Angstroms) is not absorbed by
atmospheric gases including water vapor.
The optical attenuation (extinction) of the red light as it
passes through particulates in a smoke plume is slightly
less than for green or white light. The opacity of a given
plume would be slightly less for red light than for that
measured with green or white light.
* Lidar is an acronym for Light Detection and Ranging. It is a
laser ranging system use~in remote sensing applications.
-------
2
The ruby laser is very reliable.
There is a large amount of technical information regarding
the optical properties of the atmosphere as measured and moni-
tored with the ruby laser.
All the performance evaluation and calibration tests/results given
later in this report apply only to a ruby lidar, namely, the EPA-NEIC Omega-l
Lidar. The lidar has the inherent capability of measuring plume opacity
with consistent accuracy during either day- or nighttime or under a variety
of background contrast conditions (clear sky, cloudy sky, terrain background,
etc.). This is a major advantage when used in the EPA Air Enforcement Pro-
gram, over the restricted daylight viewing hours imposed upon the reference
method. In the introduction of Method 9 the following is stated:
"Other variables which may not be controllable in the field
are luminescence and color contrast between the plume and
the background against which the plume is viewed. These
variables exert an influence upon the appearance of a plume
as viewed by an observer, and can affect the ability of the
observer to accurately assign opacity values to the observed
plume. Studies of the theory of plume opacity and field
studies have demonstrated that a plume is most visible and
presents .the greatest apparent opacity when viewed against
a contrasting background. It follows from this, and is
confirmed by field trials, that the opacity of a plume,
viewed under conditions where a contrasting background is
present can be assigned with the greatest degree of accu-
racy. However, the potential for a positive error is also
the greatest when a plume is viewed under such contrasting
conditions. Under conditions presenting a less contrasting
background, the apparent opacity of a plume is less and
approaches zero as the color and luminescence contrast de-
crease toward zero. As a result, significant negative bias
and negative errors can be made when a plume is viewed under
less contrasting conditions. A negative bias decreases
rather than increases the possibility that a plant operator
will be cited for a violation of opacity standards due to
observer error. II
While measuring plume opacity of a white-to-gray plume the reference
method has a significant negative bias due to the lower contrast between
the plume and the background (haze or clouds). Also the opacity error will
further be increased as the ambient lighting level decreases toward darkness.
-------
3
The measurement of plume opacity with the lidar is independent of plume/
background contrast and ambient lighting conditions. The significant negative
bias inherently a?sociated with the reference method is not present in the
lidar opacity measurements. The lidar mechanism measures the actual plume
opacity with greater accuracy than does the reference method.
The purpose of this report is to delineate the lidar (technical) mech-
anism, application of the lidar to the quantitative measurement of plume
opacity, and the sound test results which strongly support the proposition/
promulgation of the lidar technique as an alternate method to the reference
method.
-------
II.
SUMMARY AND CONCLUSIONS
EPA-NEIC has developed the lidar mechanism which is used as a means of
remotely measuring the plume opacity of visible emissions discharged from a
stack or other source structure. The lidar is used to measure opacity during
either day- or nighttime hours, since it contains its own optical energy source
or transmitter, irrespective of the variety of background contrast conditions
encountered in the field.
The design and performance requirements of the EPA-NEIC Omega-1 Lidar
were formulated as a result of the field diagnostics tests performed with the
EPA-RTP Lidar and the SRI International Mark IX Lidar. The proof-of-principle
of the lidar mechanism as applied to the remote measurement of plume opacity,
was satisfactorily completed with these lidars. These lidar systems each used
a solid state ruby laser as a transmitter.'
The lidar mechanism or technique is applicable to measuring smoke plume
opacity at numerous wavelengths of laser radiation. However, the performance
evaluation and calibration test/results given in this report apply only to a
ruby lidar. These tests were performed using the EPA-NEIC Omega-l Lidar.
The Omega-l Lidar was subjected to preliminary performance or first-run
tests in conjunction with an aerosol chamber which generated an effective par-
ticulate plume which had a plume thickness of 9.1 meters. The range of opacity
values in the chamber ranged from 0 to 96%. The overall standard deviation of
the lidar opacity data based upon 251 data points, was 3.1%. This value includes
the optical backscatter signal variation due to atmospheric noise along the li-
dar's line-of-sight. The mean difference was +0.3%, between the lidar opacity
values and the respective chamber opacity values over the range from 0 to about
96%. These tests established the baseline performance of the lidar and un-
covered several anomalies in the system. These anomalies were all satisfactorily
corrected.
-------
5
The Omega-l Lidar is internally calibrated with a mechanism called an
optical generator. that simulates the atmospheric and plume backscatter sig-
nals with light-emitting diodes and a solid state laser. The optical generator
is used to calibrate the entire lidar receiver. the two video channels (linear
and logarithmic) and all the remaining data processing electronics. The optical
generator is also calibrated once per month while the lidar is in field use.
This particular calibration determines the generator's actual opacity values
for the O. 10. 20. 40. 60 and 80% switch settings to within a small fraction of
a percent.
The optical generator was employed to conduct extensive calibration tests
on the Omega-1 Lidar. The calibration tests were performed on the two video
channels yielding the following results:
a.
Linear Channel - mean difference of +0.2% from 0% to 60% (nominal)
with a standard deviation of 0.6% based on 2.880 data values. The
high voltage range of the photomultiplier tube detector (PMT) was
from 1.0 KVDC to 2.9 KVDC.
b.
Logarithmic Channel - the mean difference ranged from +0.1% to -0.3%
from 20% to 80% (nominal) with a maximum standard deviation of 0.5%
based on a total of 1.950 data values. The linearity was about 0.5%
of the total bandwidth of 100 dB (10 decades). The high voltage
range of the PMT was from 1.3 KVDC to 2.1 KVDC.
These tests clearly show that the lidar is able to measure plume opacity
to within 0.3% from 0% (clear air) to at least 80% opacity values.
Finally. the Omega-1 Lidar was subjected to performance evaluation tests
with a smoke generator that is used in the certification of federal and state
visible emissions observers in accordance with the requirements of Reference
Method 9. The analyzed data showed that the lidar opacity values ranged from
0% difference to -2%. with respect to the smoke generator transmissometer. for
80% of the reduced data runs. For 93% of the reduced data runs the difference
in plume opacity ranged from +1% to -2%.
For about 7% of the reduced data
-------
6
runs the lidar opacity was slightly greater than the transmissometer value by
4% or less. In these latter data the positive error was due to ambient dust,
being generated by vehicles operating nearby, present in the near region of
the lidar's line-of-sight. These data were retained in the data set because
the standard deviations of these lidar opacity valves were less than the 8%
limit in the Opacity Data Acceptance/Rejection Criterion (Section VIII).
The calibration and performance evaluation tests have clearly demonstrated
that the lidar is an acceptable alternate method to Reference Method 9. The
required correlation during the performance evaluation tests was not carried
out with visible emissions observations, due to their inherent negative bias,
but with the smoke generator1s white-light transmissometer.
These are numerous advantages of using the lidar for the measurement of
smoke plume opacity. The most important advantages are the following:
Its inherent, absolute accuracy in measuring the opacity of a plume,
being significantly greater than that obtained with the Reference
Method.
Its capability of measuring plume opacity
well as during daylight conditions, which
plished with the Reference Method.
during nighttime hours as
cannot be effectively accom-
Its inherent capability of measuring plume opacity with consistent
accuracy and nonsubjectivity independent of background light con-
trast conditions such as between a plume and clear sky, cloudy sky
or terrain background, etc. The color contrast between the plume
undertest and the background sky or terrain has no bearing on the
lidar's performance since the only data required is the atmospheric
optical backscatter signals from just before the plume and just
beyond or behind the plume. If the lidar line-of-sight terminates
against either terrain or a cloudy sky, this will not affect the
lidar opacity measurements. However, the lidar cannot make accurate
opacity measurements while looking directly into the sun or during
precipitation conditions.
-------
7
By definition it is usual that the alternative method gives a negative
bias (lower value and possibly less accurate) for a given test parameter or
variable with respect to the reference method. But with the lidar mechanism
this is not the case.
While measuring plume opacity of a white-to-gray plume the reference
method has a significant negative bias, as documented in the introduction of
Method 9, due to the lower contrast between the plume and the background (haze
or clouds). Also the opacity error will further be. increased as the ambient
lighting level decreases toward darkness.
Since the measurement of plume opacity with the lidar is independent of
plume/background contrast and ambient lighting conditions, the significant
negative bias and negative errors inherently associated with the reference
method is not present in the lidar opacity measurements. The lidar mechanism
measures the actual plume opacity with greater accuracy than does the refer-
ence method.
Under less-than-ideal background-to-plume color/luminiscent contrast con-
ditions the reference method cannot be effectively used to verify the data
obtained with this method because of the significant negative bias and nega-
tive errors. The same holds true with using the lidar to measure plume opacity
at night. The reference method cannot be used to verify the data obtained
under this method.
It is suggested that an industrial facility, etc., use a white-light trans-
missometer, properly positioned, calibrated, and operated, to verify the opacity
values concurrently recorded with the lidar. This is especially suggested
during nighttime operations. (Some new source performance standards now require
in-stack transmissometers to measure opacity).
The lidar has two basic integrated constituents, the laser transmitter
and the electro-optical receiver. The laser transmits an extremely short
pulse (nearly 5 meters in lenQth) of light toward a visible emissions plume.
This light pulse is partially backscattered to the lidar receiver by aerosols
-------
8
(particulates) from three distinct regions along the lidar's line-of-sight or
instantaneous field-of-view:
1.
The atmospheric path before the pulse reaches the plume,
2.
The plume itself,
3.
The atmospheric path beyond the plume, after the pulse has passed
through the plume.
The backscatter light signals from regions (1) and (3), corrected for
1/R2 fall-off (optical backscatter signal amplitude decrease as a function of
lidar range through the atmosphere), are the optical data used to calculate
the optical opacity of the plume under investigation. By the mathematical
ratio of the signal from region (3) to that from region (1), the lidar deter-
mines the square of the optical transmittance (T 2) of the plume. The square
p
of the plume transmittance is determined because of the lidar pulse passes
through the plume twice. The lidar pulse goes out through the plume and sub-
sequently is backscattered by the atmospheric aerosols beyond the plume
[region (3)]. This backscatter signal then returns through the plume to the
lidar receiver.
The backscatter signals are converted to electronic signals in the lidar
receiver. These signals are directed into the data processing intrumentation
which calculates the square of the plume transmittance (T 2), the plume trans-
p
mittance (T ) and then the plume opacity, 0 , 0 = 1 - T. The opacity value
p p p p
for each lidar measurement or firing is permanently recorded in a hard-copy
format along with its respective data and time data. The original lidar re-
ceiver data (optical backscatter signal amplitude vs. lidar line-of-sight range)
along with date, time, source identification, etc., are recorded on the system's
computer-controlled magnetic tape assembly as an evidentiary record for future
reference or additional calculations.
The lidar has the capacity to record a backscatter signal once-per-second.
The nominal recording or data rate employed is one backscatter signal every
10 seconds (6 per minute) which may be continued for a matter of minutes or
even hours.
-------
9
The lidar computer performs an opacity calculation for each backscatter
signal recorded through the plume under-test. Also the analysis is repeated
on the EPA-NEIC laboratory computer for the highest practicable accuracy. All
the opacity values, 0p' calculated for a given data run, which may be minutes
or hours in length, are reduced in accordance with the requirements of the
regulation to be enforced. This is accomplished with a running average mecha-
nism which locates the highest average opacity, 0 , values(s) for the required
p
time interval (example 5 or 6 minutes) in the data run. Any violatiions of
the applicable regulation are ascertained from these reduced data (Section
VIII of this report).
The Omega-1 Lidar has a Holobeam Model 624 ruby laser as an optical
energy transmitter, an 8-inch reflective telescope as a receiver for the laser
energy backscattered from the lidar's line-of-sight through the localized at-
mosphere, and a specialized photomultiplier tube (PMT) as the optical detector.
Once the detector has converted the optical backscatter signal to an elec-
tronic video signal in a amplitude vs. lidar range format, the video signal
then is directed into one of two video channels. They are the linear and the
logarithmic channels." (The logarithmic channel is used when a large signal
dynamic range is required such as in urban areas where the particulate load-
ing in the localized atmosphere is quite high). The output signal of each
channel is fed into a Biomation Fast Transient Recorder (digitizer) that con-
verts the analog video signal into a digital signal which is compatible with
the lidar computer. The computer processes the video data from either of the
two channels and calculates plume opacity. The computer also records the
video signal on magnetic tape as an evidentiary record.
The beam divergence or spread of the laser pulse was measured to be 0.2
milliradians which means that at 1 km from the lidar the pulse is 20 cm (8 in)
in diameter and at 1 mile it is 13 inches. The plume diameter must be larger
than the pulse diameter at the desired range of the lidar from the source under-
test.
-------
10
The Omega-l Lidar also has the capability to perform spatial or temporal
monitoring of the following:
a.
plume drift and dispersion characteristics/dynamics,
b.
plume behavior such as fumigation, coning, etc.
c.
location and movement of the combining of plumes,
d.
plume density variations,
e.
vertical burden and inversion layers.
An intensive laser safety program has been developed and pla~ed into opera-
tion at EPA-NEIC for both the field use and maintenance of the Omega-1 Lidar
(Section VII).
The Omega-l Lidar is an accurate mechanism for the measurement of plume
opacity during all hours of the day and night, regardless of background con-
trast lighting conditions such as dark or cloudy skies. The extensive test
results obtained with this lidar are quite sound, and they strongly support
the proposition/promulgation of the lidar technique as an alternative method
to Reference Method 9.
-------
III.
BACKGROUND OF THE LIDAR
The first application of a lidar was for meteorological purposes in the
lower atmosphere at the Stanford Research Institute in 1963.1'2 Also, early
work in lidar involved the detection and recording of backscattered echoes
from turbidity in the upper atmosphere and the backscatter from atmospheric
molecules and haze. In the time period from 1967 to 1969, the lidar was de-
veloped into a remote sensing instrument that was used in many diverse scien.
tific applications. Also, research in this time period revealed important
applications of the lidar in air pollution monitoring. The major thrust in
lidar field usage has been in atmospheric probing, meteorology, and air pollu-
tion monitoring.
o
The lidar with a pulsed ruby laser (wavelength of 6943 A, red light) used
as the optical energy transmitter, has been used extensively in the last seven
years, especially in the monitoring of smokestack particulate emissions along
with the subsequent particulate plume dispersion characteristics and behavior
as a function of local meteorological and atmospheric conditions.3-22 In 1969,
a cooperative research program was initiated to demonstrate the utility of the
ruby lidar to quantitatively measure smoke plume (visible emissions) opacity.*
The EPA Research Triangle Park (EPA-RTP), the General Electric Company and the
Edison Electric Institute4,15,19,20 effectively carried out studies to show
the proof-of-principle for using a ruby lidar for the measurement of smoke
plume opacity. During this effort a mobile lidar system (EPA-RTP Lidar) was
designed, fabricated, and fJeld tested. The detailed evaluation of this lidar
was conducted from 1969 to 1971 which yielded valuable results regarding the
lidar instrumentation and its field usage. 19 The tests provided a more practi-
cable design for the photomultiplier tube (PMT) detector.
* Opacity is defined as one minus the smoke plume optical transmittance
(O=l-T).
-------
12
The after-pulsing (detector recovery after plume encounter) characteristics of
the lidar's PMT dictated a design change to eliminate the effects of the large
optical backscatter signal resulting from the interaction between the laser
pulse and the plume particulate matter. As a result, a temporal gating scheme
was devised for the PMT and subsequently incorporated into the lidar system
electronics. An inverse-range squared (1/R2) correction mechanism was also
incorporated into the lidar electronics to effectively correct for the l/R2
received-signal amplitude decrease, providing an improved means of calculating
plume opacity from the lidar receiver data.2o
The evaluation also provided information regarding the processing of the
lidar data (lidar pulse backscatter return signal vs lidar range) in the cal-
culation of plume opacity in addition to the need and approach for the field
calibration of the lidar.
In the EPA-RTP Lidar system, the electronic signal from the receiver was
displayed on an oscilloscope (A-Scope). The scope trace was photographed with
a polaroid scope camera. Opacity was calculated from the physical measurements
of the respective voltage levels or amplitudes taken from the photograph.
This evaluation and subsequent studies in the field clearly indicated a need
for a more accurate and reliable data processing mechanism. It was determined
that the lidar receiver data should be converted from analog to a digital format
and processed by a small computer or programmable calculator. Opacity calcula-
tions could then be carried out at a much faster rate than was available in
this lidar.
This evaluation also pointed out a need for a viable means of system cali-
bration in the field. Synthetic targets were designed and fabricated to simulate
plume opacity values. The optical transmittance and opacity of the five synthetic
targets were quantitatively determined in the laboratory. The agreement between
the laboratory value and the lidar-measured value of the opacity of each target
was quite good. In 1975, EPA/RTP performed the calibration tests again using
a set of newly fabricated screens.23 The agreement between the lidar and lab-
oratory determined values was quite good.
-------
13
In December 1975, the Stanford Research Institute (SRI) under contract to
the EPA National Enforcement Investigations Center (EPA-NEIC), carried out a
cooperative field evaluation of their Mark IX Mobile Lidar. The Mark IX has
the data processing features that the aforementioned EPA-RTP lidar evaluation
revealed as being needed. This evaluation involved the actual field testing
of this lidar with the use of a smoke plume generator, visible emissions from
several industrial smokestacks (day and night) and lidar calibration test
screens. This testing clearly demonstrated the value of a lidar for obtaining
smoke plume opacity of stack emissions during day- and nighttime hours of opera-
tion. Its quick set-up time (approximately 3 to 5 minutes from the time the
truck stopped) and ease of operation in addition to being a remote sensor, has
demonstrated a great utility for the EPA enforcement monitoring program of
particulate emissions. These field tests as well as the field tests periodical-
ly carried out with the EPA-RTP Lidar served as an excellent technical baseline
for the optical, mechanical, and electronic design of the EPA-NEIC Omega-1
Lidar System. This lidar will be discussed in Section V of this report.
It is noteworthy to mention that SRI has conducted extensive research
(some EPA sponsored) into the optical backscatter properties and behavior of
smokestack emissions as well as plume behavior/characteristics as related to
atmospheric/meteorological conditions.5'lQ,14,16,17 The resulting data and
conclusions of this research effort are of high value at this time as well as
in the application to future development of lidar as a quantitative air pollu-
tion monitoring instrument.
-------
IV.
THE BASIC CONCEPT OF LIDAR
A basic lidar consists of an optical transmitter, an optical receiver and
associated signal processing electronics. A laser is employed as a transmitter
o
for pulsed optical energy. Usually a ruby (wavelength of 6943 A, red light
transmitter) laser is used to generate the optical or light pulses. They nomi-
nally produce these light pulses having a peak power of 30 to 150 megawatts,
with a pulse duration of 10 to 30 nanoseconds (10-9 sec = 1 nanosecond). The
optical pulses are transmitted toward a target such as a smokestack plume, in
a highly collimated beam [Figure IV-I]. The optical energy (laser pulse) is
transmitted through the intervening atmosphere to the target of interest and
is backscattered along this path toward the lidar receiver. In the case of
the ruby laser the red light backscattered by the atmospheric path of propaga-
tion and the target is collected by the lidar receiver, usually a reflective
telescope, and detected by a photomultiplier tube (PMT). The PMT converts the
optical signal collected by the telescope into an electronic signal which is
in turn displayed on an oscilloscope for viewing by the lidar operator. The
oscilloscope's presentation to the operator is in the form of backscatter signal
amplitude as a function of range along the lidar's line-of-sight [Figure IV-2]
which is called an A-scope presentation. There are important features of a
typical scope presentation in this sketch. The scope trace increased quite
rapidly at the left, to a peak which corresponds to the spatial point of the
convergence of the fields-of-view of the lidar receiver and the beam size of
the laser [Figure IV-3]. The trace then decreases or falls off in amplitude
as 1/(lidar range)2 [(1/R2)] in accordance with the general lidar equation.!
The spike in the trace is representative of a backscatter signal from a smoke
plume. Its amplitude is much greater than that of the atmospheric return be-
cause the particulate density if far greater in the plume than in the surround-
ing air. The physical and mathematical treatment of the scattering of the
laser light by the particulates (aerosols) in the ambient air and in a smoke
plume is called Mie Scattering Theory24'26 and will not be discussed here.
-------
~~
0'"
~
~O
~~
~~ ~~
0'" c,1>-
~ ~
~O c,+-
~~ ~I>-
~\ v
~~
~~I>-
SMOKE PLUME
13
Figure IV-J Typica' Lidar FiQ'd Set-Up
I-'
(.J1
-------
Plume Backscatter Signal
Convergence Distance or Point
Zero Signal Level
Lidar Range or Time
..
(400 nanoseconds/division)
16
Atmospheric
Backscatter Signal
Signal Falls Off In
Amplitude As 1/R2
From The Point Of
C onvergen ce
Figure IV-2 Oscilloscope Presentation, Signal Amplitude vs Range
(A-Scope), Uncorrected For 1/R2 (Optical Generator)
-------
Telescope Field-Of-View (FOV)
Lidar Receivingtrelescope
,.. ~ .
Laser Beam Size
/
Transm itter
Las e r
Point of Of Laser Beam - Telescope FOV Convergence or Overlap.
Figure IV-3 P ictoral Diagram of Of The L idar Transm itter - Rece iver Convergence
......
........
-------
18
The behavior of the backscattered light resulting from the laser pulse
propagating through the atmosphere is given by the general lidar equation.I,7
Pr(R) = Pt l ~~:) A exp [ -2J: a (r) dr ]
where:
P (R)
r
Pt
l
c
t
t
~(R)
A
1/R2
a(r)
(IV-I)
is the instantaneous received optical power at the
which is a function of lidar range R R = c(t-to)
,
2
lidar receiver,
is the transmitted optical power at time t (time of transmission
of the laser pulse) 0
is the effective laser pulse length, l = ct/2
is the speed of light,
is the pulse duration t = (tl-tO)' which is approximately 10 to 30
nanoseconds,
is time,
is the volume backscatter coefficient of the atmosphere along
the path of the laser pulse,
is the effective area of the telescope receiving aperture,
is the term for the optical backscatter signal amplitude decrease
as a function of lidar range. If a particle distribution back-
scatters laser light at a distance R from the lidar then the signal
amplitude at the lidar receiver is P (R); if an identical particle
distribution backscatters laser light at a distance of 2R, then
the signal amplitude at the lidar receiver is P (R)/4.
r
is the atmospheric volume extinction coefficient along the path
of the laser pulse, where r is a range variable of integration.
The exponential term given in Eq (IV-I)
exp [ - 2 J: a (r) dr ]
(IV-2)
-------
19
is the atmospheric attenuation term where a(r) is integrated over the atmospher-
ic lidar range to a target under question at range R. This equation covers a
distance of 2R, a distance (lidar range) R out to the target and an equal dis-
tance back to the lidar receiver. As a laser pulse is propagating through the
local atmosphere, the effect of this term serves to attenuate the beam signifi-
cantly depending upon the functional dependence of a(r) upon r. The effect of
a(r) is laser light extinction which includes light absorption and scattering
by the molecules and most importantly, the particulates (aerosols) in the inter-
vening atmosphere. In relatively clear air conditions the extinction coeffici-
ent a is small, while in polluted air conditions the extinction coefficient is
large and the laser beam in question is attenuated quite rapidly, thus limit-
ing the effective or probing range of the lidar.
The magnitudes of a and ~ are dependent upon the wavelength of the incident
lidar energy and the number, size, shape (spherical, aspherical, cylindrical,
etc.) and refractive optical properties of the particles illuminated in a given
unit volume. The shape, size and number density of the particulates being
emitted from an emissions source greatly influence the magnitude of the optical
backscatter signal collected by the lidar receiver, the size of the spiked
plume signal in Figure IV-2.
The volume extinction coefficient of the atmosphere, a, is generally re-
lated to the volume backscatter coefficient ~ which is largely due to optical
scattering. A necessary condition for solving the general lidar equation is
that ~ and a must be related quantitatively. Knowledge of the magnitude of ~
and a and their relationship is not necessary for the lidar measurement of
plume opacity as is clear in the derivation of the lidar opacity equation later
in this section.
Plume opacity is determined by measuring the plume transmittance (T) with
the lidar. Opacity is defined as:
o = 1 - T
P
(IV-3)
-------
20
where:
o
o is the plume optical opacity* at 6943 A.
p
o
T is the plume optical transmittance at 6943 A.
Plume opacity is measured with the lidar in a field test set-up depicted
in Figure IV-I. The fundamental measurement made with the lidar is the square
of the transmittance (T2) of the smoke plume due to the fact that the lidar
light pulse must pass through the plume twice. The mechanism of this measure-
ment is now discussed in detail.
The lidar opacity measurement mechanism is depicted in Figure IV-4. A
lidar pulse is transmitted from the laser with signal intensity 10 into the
so-called lidar near region [Figure IV-4]. Along this atmospheric path of
propagation made up of molecules and aerosols with occur naturally, the lidar
pulse is partially backscattered toward the lidartelescope receiver with a
signal intensity I. The smoke plume also backscatters a portion of the lidar
n
pulse back toward the lidar receiver with a signal intensity I. The remainder
p
of the lidar pulse is attenuated as it passes completely through the smoke
plume. The magnitude-of the pulse attenuation is directly related to the trans-
mittance of the plume. Along the far region atmospheric path of propagation,
the pulse is now backscattered toward the lidar receiver. However, this far-
region backscatter signal must again traverse the smoke plume resulting in
further signal attenuation directly related to the plume optical transmittance.
This signal has an intensity If having been attenuated by the plume twice in
the amount of T2. A typical signal displayed on the lidar receiver's scope is
shown in Figure IV-2. This signal is systematically corrected for the I/R2
amplitude decrease or fall-off yielding a scope trace as shown in Figure IV-5.
* Opacity is also measured in the field through visible emissions observers
trained and certified in accordance with Reference Method 9, November 12,
1974, Federal Register.
-------
ATTENUATED LIDAR PULSE "(.~~
THROUGH THE PLUME I' Vp..~ ",
+-tb ",
p..v ../
~~ ,
. \.-V~~p..\.- /
q ,0
/y
Near-Region of Lidar's Line-of-Sight
Through the Local Atmosphere (C lean Air)
NEAR -REGION
BACKSCATTER SIGNAL
I
REGION OF PLUME
OPTICAL
BACKSCATTER
Ip
IF
LlDAR
SMOKE STACK
Figure IV-4 Lidar Opacity Measurement Mechanism
FAR-REGION
BACKSCA TTER SIGNAL
Far-Region of l,.idar's
Line-of-Sight Through
the Local Atmosphere
(C lean Air)
I\.)
.....
-------
Plume Backscatter Signal
Point
22
Atmospheric Backscatter
Signals Corrected
For 1/R2
Zero Signal Level
Lidar Range or Time-
(400 nanoseconds/division)
Near Region
1
IN
\
Figure IV-5 Oscilloscope Presentation Signal Amplitude vs Range.
Corrected For 1/R2 (Optical Generator)
Far Region
i
IF
1
-------
23
In a basic sense, the square of the plume transmittance is obtained by taking
the ratio of If to In [Figure IV-S].
T2 = If
r
n
(Two Way)
(lV-4 )
The one-way lidar-measured smoke plume transmittance is obtained by taking the
square root of Eq (IV-4).
T = ( :J ~
(one way)
(lV-S)
Finally, the smoke plume opacity is given by Eq (IV-3)
o = 1 - T =
P
1 -( :~ r
(lV-6 )
To have opacity in percent, 0 is multiplied by 100.
P
The backscatter signal [Figure IV-4] from the smoke plume is not used for
the measurement of plume optical transmittance or opacity. This signal is
used to monitor plume drift and dispersion behavior as well as the spatial and
temporal combining of "two or more smoke plumes located in close proximity of
each other.
Research4'10 has shown that valid optical smoke plume opacity measurements
may be made by observing the near- and far-region clear air returns [Figure IV-4]
o
at the ruby lidar wavelength of 6943 A. The lidar has been used in the field
for measuring the opacities of actual visible emissions plumes.21 The field
tests were quite successful during both day and night plume monitoring. The
ruby lidar technique is ready to be used to gather smoke plume opacity data on
a single shot basis or over-extended periods of time with a variable pulse
rate up to 1 pulse-per-second in EPA enforcement applications.
-------
V.
DESCRIPTION OF THE EPA/NEIC OMEGA-l LIDAR SYSTEM
The research and development that has been carried out within EPA and in
private institutions has provided the necessary technical base for the design,
fabrication, and testing of the Omega-l Lidar. Research lidar instrumentation
had been conceived, designed, and tested in the laboratory environment and in
the field, providing much technical and operational insight into the requirements
of a lidar system in addition to the pragmatic considerations that are encoun-
tered in the field. All parts of the lidar system from the laser transmitter
through the data processing electronics to the computer have been optimized
and improved for field use in enforcement applications. The design for the
vehicle, within which the lidar is mounted, was derived from the information
obtained from the research lidar units.
In late 1975 and early 1976 the Omega-l Lidar design was
technical specification was prepared. In mid-1976 a contract
tion and testing was awarded to the General Electric Company.
also fabricated the EPA-RTP research lidar several years ago,
a technical building block for this lidar.
formulated and a
for the construc-
This Company
which served as
The Omega-l Lidar consists of the following major assemblies:
l.
2.
3.
4.
5.
6.
laser transmitter/pedestal
optical receiver assembly
receiver electronics
automatic data processing/recording
electrical generator assembly
truck/van enclosure
assembly
instrumentation
A schematic diagram of this lidar is given in Figure V-l.
-------
~i9ht PUlsel
..
Signal
Neslab
H X -100
Cooler
'Aiming Telescopel
I
Celestron
8-inch
Reflecting
Telescope
ITT 4084
PMT
Narrow Band Optical Filter
ptical Generato
alibration Mech
TRANS~ITTER / RECEIYU
1111
w r-.
C,...,e::GR
I
I
,
,
I
I
I
I
I
Laser
Remote
Station
Q Switch
Remote
Station
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
Logarithmic I
Channel Signal
SIG~AL PROCESSING
figure V-J. Schemof;c Diogrom 01 fhe Omego-J lidor System
nalog
t 2 Generator
/R2Correctio
Logarithm ic
Amplifier
Linear Channel
Signal
Signal
Suppression
Gate Generators
(two)
I
I
I
I
I
I
I
: CO~TROl AND ANALOG
,
I
PMT Power
Supply
ektronix
R475
Oscilloscope
Scope Camera
Digital
Signal
Video
B iom at ion
8100 Fast
Transient
Recorder
HP 59309
Digital
Clock
Dig ital V ideo
Signal
HP 9825A
Computer
(DigitaI1/R2
Correction)
DATA PROCESSI~G AND RECORDIMG
N
(J'I
-------
26
The first major assembly, the laser transmitter, is the Holobeam Laser,
Inc., Model 624 Q-Switched ruby laser. Its pertinent characteristics are given
in Table V-I.
Table V-I
MODEL 624 LASER CHARACTERISTICS
Wavelength of Transmitted Lighta
o
6943A (red)
Ruby Rod Dimensions
0.95 cm X 15.2 cm
(0.38 in X 6 in)
Pulse Width (FWHM)
15 nanoseconds nominally
Maximum Output
3.30 Joules (single shot)
2.95 Joules (at 1 pulse/sec)
0.2 Joules (at 22°C, just
ab"ove threshold)
Minimum Output
Pulse Repetition Rate
(maximum)
1 pulse/second (pps)
(variable selection between
single shot and 1 pps)
Laser Cooling
Water
Closed Cycle Refrigerated
Laser Head Beam Divergence
(full angle)
1.1 mrad, single shot
1.9 mrad, 1 pps after 25
minutes continuous operation.
Laser Up-Collimator Ratio
6: 1
Beam Divergence past Up-Collimator
0.2 mrad, single shot
0.3 mrad, 1 pps
Beam Diameter Out of Up-Collimator
3.7 cm (1.5 in) (effective)
Laser Optical Train Structure
Invar rails
a The choice of the ruby laser was given in Section I of this report.
-------
27
In order to reduce the angular divergence of the laser beam, an up-colli-
mator (collimating telescope) was incorporated on the front of the laser. It
reduces the beam divergence to approximately one-sixth that of the original
laser beam. The beam diameter at'l km from the 1idar is about 23 cm for single
shot operation and 33 cm for the rapid fire operation (after about 25 minutes
of continuous operation). At a distance of 500 meters the beam diameters are
half those given above or 12 cm and 17 cm, respectively. The diameter of a
plume under test with the 1idar, must be larger than these values for the re-
spective lidar range values. If the plume diameter is less than the beam dia-
meter at a given 1idar range, erroneous opacity values would result. Then the
lidar would have to be moved closer to the source. This is not a practical
constraint as most smokestacks and other sources of visible emissions produce
a plume with a horizontal thickness or diameter. much larger than these values.
The lidar receiver consists of a reflecting telescope for the optical
collector and a light detector (photomultiplier tube (PMT)). The pertinent
characteristics of the receiver are given in Table V-2.
Table V-2
OMEGA-l LIDAR RECEIVER CHARACTERISTICS
Photomultiplier Detector (PMT)
Lidar Aiming Mechanism
Ce1estron Pacific Model C8L
fllO Schmidt-Cassegrain
Compound Telescope
20.3 cm (8 inches)
203 cm (80 inches)(effective)
4 mrad full angle
° °
13 A (FWHM) Centered at 6943 A
at 23.9°C (75°F)
ITT Model F4084 (8 dynodes)
Direct view through Celestron
telescope or an aiming tele-
scope boresighted with the
Celestron and the laser trans-
mitter.
Telescope
Aperture
Focal Length
Field of View
Narrow Band Pass Filter (FWHM)
-------
28
The laser and the telescope are mounted side-by-side on a Pelco mount
that is adjusted to turn !95° horizontally about the longitudinal axis of the
lidar van, and from -100 (declination) to +900 (straight-up) in the vertical
about the same axis.
The electronic video signal from the PMT detector is directed into the
lidar's signal processing electronics forming two video channels:
. Linear channel
. Logarithmic channel.
Linear Channel
The signal in the linear channel is basically the PMT video signal, Figure V-l,
which is linear in the PMT's specified operating range, without any additional
amplification. The linear video signal varies in amplitude in direct proportion
to the magnitude of the optical input signal to the PMT.
The linear channel has many uses.
opacity, monitoring of the combining of
characteristics and dynamics, and other
range is not required.
It is used in the measurement of plume
plumes, monitoring plume dispersion
uses where high video signal dynamic
The linear video signa127 is fed into one input channel of the Biomation
8100 Fast Transient Recorder (digitizer) where is it digitized, being converted
into a series of digital numbers or words [Figure V-l]. This digital video
signal or waveform is then displayed on the Tektronix R475 oscilloscope.
Photographs of the oscilloscope showing typical linear channel data in an
A-Scope format [lidar signal amplitude vs. range (lidar round trip range =
speed of light. time/2)] are provided in Figures V-2 and V-3. The photo in
Figure V-2 is a linear channel waveform for clear air. This waveform was gen-
erated with the optical generator used for system calibration [Figure V-l].
-------
29
Backscatter Return Signal Decays as 1/R2
Transmitter - Receiver Convergence Point
System Trigger
1
I/)
Zero Signal Level-
Lidar Range or Time
(1 microsecond/division)
.
to = 710 nanoseconds from system trigger
Note:
The convergence point is about 1250 nanoseconds from system
trigger. and 540 nanoseconds from to'
Figure V-2 Linear Channel Video (Atmospheric Backscatter) Signal
For Clear Air, Uncorrected For 1/R2 (Optical Generator).
-------
Convergence Point
Zero Signal Level
Note:
Plume Spike
(Near Region)
(Far Region)
!
II
"0
:J
:!::
Q.
E
~
II
c:
CJI
fJ)
Lidar
Time or Range
.
(400 nanoseconds/division)
This oscilloscope photograph is a double exposure
showing clear air signal coincident with the plume
5 ign al.
Figure V-3 Linear Channel Video Signal, 20% Opacity
(Uncorrected For 1/R2) (Optical Generator)
30
Attenuation In Optical
Signal Due To Plume
Normal Clear Air
Return Signal
-------
31
For further explanation of the waveform, the system trigger (receiver turn-on),
labeled in Figure V-2, occurs when the Pockel-Cell Q-Switch in the laser1s
optical train is activated. The time-zero value, t , occurs 710 nanosec after
o
system trigger which is the time reference value for all lidar range measure-
ments. The PMT output level is at the zero signal level during this time inter-
val [Figure V-2]. At t the laser pulse emerges from the laser's upcollimator,
o
which was measured empirically. This is the reason why t has been defined in
o
this manner. All lidar range measurements are calculated from the time interval
required for the laser pulse to travel from the laser to the target in question
and return to the lidar's receiver. The transmitter-receiver convergence dis-
tance is adjusted for 80 meters from the lidar, 540 nanosec from t and 1250
o
nanosec from system trigger [Figure V-2].
The oscilloscope photograph shown in Figure V-3 is a linear channel wave-
form (A-Scope) resulting from the encounter of the laser pulse with a particu-
late plume whose opacity is 20%. The departure of the waveform from clear
air, due to the plume encounter, is depicted in this photograph. However, the
signal is still linear and decreases or decays in amplitude, both before and
after the plume, as 1/R2 (Eq IV-I).
The amplitude of these signals [Figure V-2, V-3] is controlled by the
high voltage value selected on the PMT detector1s power supply and by the Bio-
mation's input signal voltage controls. The output of the Biomation unit,
displayed on the oscilloscope, is comprised of 2048 equal range or time cells
along the horizontal axis of the two-dimensional display, and 256 digital ampli-
tude counts along the vertical axis. The Biomation unit has an inherent resolu-
tion of 1 part in 256 or 0.4%. The time uncertainty is less than 2 nanoseconds.
The performance evaluation results for the linear channel are given in
Section VI of this report.
-------
32
-
Logarithmic Channel
The major utility of logarithmic channel is the quantitative measurement
of high-plume opacities in the range of 50 to 100%, especially in urban areas
where the ambient particulate burden or levels are quite high, resulting in a
large range of optical backscatter signal amplitudes. This channel is employed
where this high signal dynamic range requirement is present. An example of
this usage is the monitoring of plume opacity with the lidar located at distances
of 2 to 5 km from the source being monitored.
In this channel, the linear input signal from the PMT is fed directly
into a logarithmic amplifier. The output signal from this amplifier is a loga-
rithmic function of the linear input signal. This amplifier deamplifiesCgain
<1) large amplitude lidar return signals while amplifying small amplitude sig-
nals (gain »1) to a much greater level. In summary, the logarithmic channel
provides a much greater overall dynamic range within the lidar1s signal proces-
sing electronics. It also extends the spatial range over which plume opacity
can be effectively measured with the lidar due to the large amplification of
the low-level near-region and far-region backscatter signals.
The logarithmic amplifier, manufactured by Aertech (Model
has an overall dynamic range of 100 dB* with an inherent error
less than ~1.0 dB. The performance evaluation results for the
channel are given Section VI.
LDN-1000-l),
(linearity) of
logarithmic
Figure V-4 shows a logarithmic channel video signal resulting from a laser
pulse propagating through a plume of 85% opacity. The characteristics of ~his
photograph are basically the same as those for the linear channel [Figure V-3].
However, it is noticed that the signal level at the convergence point is much
less than (nearly half) the same respective point in Figure V-3. The signal
*
dB = decibel, a unit of the ratio of two power or intensity values,
dB = 10 10910 ::
12
-------
33
Plume Spike
(Near Region)
(Far Region)
Zero Sign al Level
Lidar Time or Range ..
(400 nanoseconds/division)
Figure V-4 Logarithmic Channel Video Signal, 85% Opacity
(Uncorrected For 1/R2) (Optical Generator).
Plume Spike
Zero-S ignal
1
Q)
'U
:I
-
a.
E
~
lIS
c
C)
II)
Lidar Time or Range .
(400 nanoseconds/division)
Figure V-5 Logarithmic Channel Video Signal, 85% Opacity
(Corrected For 1/R2) (Optical Generator).
-------
34
level beyond the plume spike (in range) would be near zero in the linear
In the logarithmic channel the signal is much greater in amplitude. The
corrected signal derived from Figure V-4 is shown in Figure V-5.
channel.
1/R2-
As in the use of the linear channel, the amplitude of these logarithmic
channel signals is controlled by the PMT power supply high voltage value and
by the Biomation unit1s input signal voltage controls. The output of the Bio-
mation unit, displayed on the oscilloscope, is comprised of 2048 range or time
cells (uncertainty less than 2 nanoseconds) along the horizontal axis of the
two-dimensional display. There are 256 digital amplitude counts along the
vertical axis with a resolution of 1 part in 256 or 0.4%.
Since there are 256 counts in amplitude and dynamic range of the logarith-
mic amplifier is 100 dB, the value of each digital count in the logarithmic
channel is 0.39 dB/count.
The logarithmic function, being nonlinear in nature, does not represent
the same relative opacity value for a given signal drop, throughout the opacity
range from 0 to 100% as given in the linear channel. The function is plotted
in Figure V-G. The value of each digital count (0.39 dB) represents a greater
opacity difference at lower values than at higher values. This is more easily
seen in Figure V-7. This figure shows the magnitude of the effect of ~l digital
count as a function of plume opacity. At 10% opacity the count error could be
! 4%, at 50% it could be about 2% and at 80% it could be about 0.9%.
With the magnitude of the error of ~l digital count established in Figure
V-7 as a function of plume opacity, it is noteworthy to assess the effect of
this error upon the logarithmic channel's ability to quantitatively measure
plume opacity.
Referring to Figure V-7, the digital count (bit) error magnitude is plotted
as a function of plume opacity for the logarithmic and the linear channels. For
the linear channel, the count error is zero from 0 to 4% opacity. It is rounded
(to the nearest percent) up to 1% from 4 to about 55%. It is 1% from 55 to 78%.
From 78 to 100% the count error magnitude increases from 1 to 8%, as shown in the
-------
lQYi~:\~.. --r-------~-- --,- ~--
g~ ,__H --~~~--~~~_:- --1-~-'-_:____'__H___- i-- -+- ~- --- ----
BC:.:) ~--------~-_:_-~------:--------------- ----- '------
7Ce) ~ . ---:--+-~,-_:, ---- ~~. ~~--~~-~~-'-_._----~--~~
I I ~--T-~ ---~- : . -: . i 'I " .
:: ------- -j--- -~-T---=:~~~~ :~i_u_lJ--'-:--~~----~--=-! - - I -:-_~;_n~_-
- -! t! 1; ,f .
---_J- ___1______- I --------.----_.!._--------f..-----.~-- +--~~--- ----i---';""'.----: - .+__.,1_1- - -- -.- - -,.....---------- -.~. -----..--~...- .-t
- - - ., ! : ii--;r i tl ii' . ;'1 :' iJ j , . : i ,. : i
3~ r ---- j L 11'-.-'-1.. 1,i --t --I' , - - " -~. r--:+-T:--~, -1 1,,1,"" . + - -... J ' ' .' ml,I+-pT
,@ '~-.-IL_-T~-:-~..t, il I ,. i-~~-+~1Y--i-+r+ '---+j-I , i '
. - . - ---11 : -1,' .., I i u- -I,' !' . . " I -iu; I + -, ,Ii, , ,I ' 'im ,I
I', i' I 1 I: l:: ~ i ' I: . :
! ; : ' Ii!! '1 i.
1~ -==--=:= i~=--=:--l ' 1 '-, - I~' !' -I -L-C--1;-i=-=C_~_J~n=--'~=~r=-_~+_~-~t'_-~ jn, .
~' i ~j~-T+l~, i .iib i--t 'i- f-TT i J +j-jjj ,', -u L.LL . Lt+
--, - -1---: ,',- -,- I l ,-: - -: : -'"!' I : i I l-r : !. :':
6 - - . ~' --~-r-' --~- - -t-i!. rtu-~ ' --! ~-'i--- -I-~Tn i '!Ttt~-- ---~ ~ T--,u'!-_:~---!_+i .
: -:-:-11;11' 1.1 iT --- :~-1 il}j liT r I ' ,
3~'Hr~-t~T'1 ~+111_~~_J ',' LL._tfTTiJ r-- , I
, . I I' I I '
- ' d'- r' .if ' ' " i ' ' ,.;, ",,'. " ,-' '. ! . - ""'['-I--j- \ nld~::O 10 g 1 oC ;,~:n;. ~c~~d:; w :;:;:~ :,O~ ,
, I I I . I ' uJllU I I i I ~L]
4@
I,
,...,
~
'-"
>-
-
o
III
C.
o ,
-@.1
- -- - --.--.
- ------ -- . --..
----- ----
r
I
- - - - -- + - --
. --~+.~.
, I
I !
I I
!
I
I - ~ I'
I
, i
: I
l
. ,
,
I
I
. W
~<{1
..(QI.2
-@.3 -C't.4 -@.5 :..6...7 <> B 09 .-l.@
-5 ,,6 ,,7 ..8 -9-1((:;).@
"3~rt
-£..@, .. 5~~ ~.6~~-7:Qf8~>.g:c~-.~ iJ;0;
-3
-4
-2@
..2
Signal Drop (dB)-
-------
8%
---.~.- ------ --,--' --- '---,------ ---------- - - -, ------------0-,---""'-"- -.--;0--- --------!~-~---.-._--- - .~, ~----,-_.-- --~------ ~.-~- -,-----......-.--~- ---.r------" -'---."--,
-:;::-r ' "! : :'.; .J:' , -.!' ]
~ ~ --:-.----i---'!--'~!-.'- -..-- . -_~___~L- 1__- _:___._.L~_:_~ I-~----+------! ! ---~- -~. .__.~-:
... :I I ; i . r .: . i '1 I
c: :!:: r j if! T 1
~ ~ !. i: I Figure V-7 Logarithmic And Linear -.J ' .. , ,,;', !
u ~ ~-t--i-----!--~-:;---~-:-----r--- Channels: One-Bit Resultant' ! i 'I--j--~ll--~--'-I!
Iii . i ! 1 ['j i' j . \ . . t," ... f '
...'" i !, " I," .. . I" I.. t. I ' I
.- ~ i . .: 1 I Error As A Function Of Opacity. . I' !'f . t. j . I
~! ~ .-:- T pUT-rn 1--1 !.; : 1. : f j .l~" u: ~ 'ITu- rn '11- --~ .11
i .. 1. r . " I . I . I " . t .. I . . I'!- i '[ I' I' ,
5%i-~-----I~- '-~:-~~-r~-I' 'I ---r-~-----i-~--!--.---"l--:-:-~-t--'--,--~I~-'-r~" r ~I OJ!
:,:_,,+-+-i. . :i,i_,._-'.~Ti. : i-dul-I-J~ :":tL~l~, . .-'JIo1., i. " . '4u, :. .![-~~
'" " '. t- '1' I .. 't ,... "::1:'" ..
4% ;-- -J ~~-l-----'_-----:-- -- -j~-- 1- - --~-!----~!---- --;---I.~-----:--- -~.J_--+--_:_~--~~--~---,--_u_~~'_I_:- . '-J-~-
[J, u_u[~',.,"-~'-,Lj,'--, .1.J"__--~,~i,_L_09~,~thmi~Gh.~ne,.L~L:L.J~' ...1., .L~J-.j
I :! ,J "~. I i.1 II !I .: I. i : .' t . L: 1 .1
3,,1- ~ -!_L_j_+~:--J-,~-J . ! _L~ll~ i..~.J I ,< i ~ ~--
2~i__L uL___'_~1..__Lu', uL1H_J.~'t>,,-L...J_L_l~J---. i' ,. -- __.L-~
701 ; I !.. I ' i ' . : . I. i" I .. I Ii: . j , , . .
'f', - - ~ . j. I~ - .-\ 7. ,::~e", Gr h.~ni~ . '. ...["1.... i..I-~ ~--:"~f. ~'-+, .--<~. .. -~-- -1"~'-."~',.lJ ~.. .; .'-. -.-
.,. '1' . I ' ""j !. .. , '1'-,..1. ,...'1 ..,
1o/c .. - jl ; :'; I' j .:. . I 1 I '. : . I "";,,' _L_._~__'. ,! .
t-l, . ....!.n. .L_.lu_J,~~-~j'- .1--' . . J---- -l. L)~-- ....1 . . .1'~.-Lj--u j ..-1
~- 'f. I' i ..f.. I'" .j r ,. .. "1..-1""1" [". --..j j"-': C1\
0%1 t :1 j .! [ I, j : f., j' . . j' .. Plu'me Opacity t(%) . : ~--J""J
o 5 10 20 30 40 50 60 70 80' 90 100
-------
37
figure. This effect can be understood by referring to the oscilloscope photo-
graphs in Figures V-8, V-9, and then comparing them with the logarithmic channel
photographs in Figures V-4, V-5..
In Figure V-8, which is a linear channel oscilloscope photo of an 85%
opacity plume (approximate) uncorrected for 1/R2, the signal level is nearly
zero in the far region (behind the plume). This signal being corrected for
1/R2, presented in Figure V-9, remains near zero in the far region.
In comparison of the logarithmic and linear video signals, corrected for
1/R2, there is a significant difference in signal levels in the far region
[Figures V-5, V-9]. To be more quantitative, if the near-region signal is 140
digital counts above zero signal level in both channels, then for 85% plume
opacity the signal level is 3 digital counts above the zero-signal level for
the linear channel, and 88 digital counts for the logarithmic channel. A change
of about ~1 digitia1 count (linear channel) at this opacity value represents a
33% adjustment of the total signal level in the far region, while the effect
of the count error is far less significant in the logarithmic channel (about
1% adjustment). This is graphically portrayed in Figure V-7.
The effects of the ~1 digital count error is kept to a minimum by having
the Biomation (digitizer) unit factory-calibrated once-per-year.
Depending upon the m~gnitude (signal amplitude) of the near-region portion
and the particulate plume optical backscatter signals, the electronics system
has a detector modulation gating scheme that is used to suppress these signals
to levels within the operating range of the PMT detector and the Biomation
Fast Transient Recorder. The scheme consists of two electronic gates that are
continuously variable in 1idar-range independent of each other, and also contin-
uously variable over an amplitude range of 0 dB to -42 dB (typical) independent
of each other.
-------
Zero Signal Level -
System Trigger
38
Plume Spike
r
Q)
-u
:J
....
a.
E
«
tIS
c:
C>
en
Lidar Range or Time
..
Figure V-8 Linear Channel Video Signal, 80% Opacity
(Uncorrected For 1/R2) (Optical Generator)
Zero Signal Level--
Plume Spike
r
Q)
-u"
:J
....
a.
E
«
tIS
c:
C>
en
Lidar Range or Time
..
Figure V-9 Linear Channel Video Signal, 80% Opacity
(Corrected For 1/R2) (Optical Generator)
-------
39
If the plume spike is quite high in the video signal (such as reflectance
from a white-dense plume), then gate-2 can be positioned over that portion of
the backscatter signal, and the amount of signal (electronic) suppression de-
sired can be manually incorporated into the PMT detector. The detector is
quite capable of operating in extremely large variations of signal amplitude,
however, the plume spike signal saturates the Biomation (digitizer) unit as is
indicated by the clipped or flat signal at the top of the oscilloscope display
[Figure V-9]. The shape of this signal is lost due to the clipping. The
shape and magnitude of the upper portion of the spike can be retained by using
gate-2 as shown in Figure V-IO.
In like manner, gate-l can be used to suppress the near-region backscatter
signal to any desired level from 0 dB to -42 dB. The strong near-region signal
usually comes from using the lidar in local atmospheric conditions of heavy
particulate burden. Figure V-ll shows the gate-l suppression upon the near
region signal. The amount of suppression in each gate is measured in a quanti-
tative manner. Depending upon the use of the data, the suppression magnitude
must be taken into account during data processing.
If overall signal suppression or attenuation is required, i.e., in the
near- and far-regions and for the plume spike, optical neutral density filters
are available in the lidar for this purpose. The neutral density (gray, trans-
parent) filter is installed in the receiver's optical path just ahead of the
PMT detector. The amount of attenuation provided by each filter is as follows:
Table V-3
OPTICAL DENSITY VS OPTICAL TRANSMITTANCE
Filter Optical Optical
No. Density* Transmittance (%)
1 1.0 10
2 2.0 1
3 3.0 O. 1
3+1 4.0 0.01
* Optical Density: D = -10g10 (transmittance)
Effective
Signal Drop (dB)
10
20
30
40
-------
Su ppressed P lu m e Sp ike
Zero Signal
Convergence Point
I
Q)
"U
::J
+'
a.
E
<{
!IS
c:
CI
(/)
-----
G ate-2 Width
Lidar Range or Time
..
40
T
Gate-2 Amplitude
Suppress ion
1
F igu re V -10 Su ppress ed P lu m e Sp ike,- Linear C h an ne I V ideo Sign ai,
20% Opacity (Corrected For 1/R2), Gate-2
Su ppressed Plum e Sp ike
Convergence Point
Zero Sign al Leve I
~-----
G ate-1 Width
G ate-2 Width
Lidar Range orTime---
Figure V-11 Suppressed Plume Spike And Near-Region Signal,
Linear Channel Video Signal, 20% Opacity
(Corrected For 1/R2), Gate-1 And Gate-2
Gate-1 Amplitude
Suppression
f-r
Gate-2 Amplitude
Suppression
1
-------
41
As mentioned above in this section, the output signal of the PMT is conver-
ted from an analog to a digital (computer compatible) format by the Biomation
8100 Fast Transient Recorder. The digital signal is directed from the digiti-
zer's output port into the Tektronix R475 oscilloscope and the Hewlett Packard
9825A computer which has general purpose utility.
. The computer has 22,952 bytes (11476 16-bit words) of user addressable
read/write memory, a 32-character light emitting diode (LED) display, a 16-
character thermal strip printer, two-track tape cartridge drive, three input/
output (I/O) slots for interfacing peripheral equipment, four plug-in read-only
memory (ROM) slots and a versatile keyboard. The read-only memory units provid-
ed with the HP 9825A in the lidar are the general I/O -extended I/O, plotting
and the string-advanced programming. The general I/O-extended I/O ROM adds
the instruction set necessary to command the 16-bit parallel I/O interface for
the Biomation unit and the Hewlett-Packard (HP-IB) interface bus for the digital
clock (year, date, hour, minutes, second) and the external 9-track tape drive.
This ROM also permits the fastest practicable data transfer rates. The string-
advanced programming ROM adds instructions for the fastest data manipulation
and computation modes of this calculator. The general I/O-extended I/O ROM
also allows for buffered, burst and direct memory access I/O transfers.
This computer has a two-track tape drive (using specialized cassettes)
that has a recording capacity of 256K bytes per cassette. This mechanism is
used to read in computer software used for data flow management, data recording
(alternate) and opacity calculations. It is also used in the editing, revising,
and recording computer software.
The primary lidar data recording mechanism is a Kennedy Model 9800 digital
tape transport which is interfaced with a Dylon Model 1015A magnetic tape con-
troller/formatter. The data density on the tape is 800 bits-per-inch (9 track).
Data recording speed is 25 inches-per-second (ips). The tape drive/formatter
combination is a NRZI ANSI (IBM) compatible system which is compatible with
EPA/NEIC's PDP-11-70 laboratory computer system, used for data processing.
-------
42
The tape drive uses 8.5-inch diameter tape reels, and the tape is 1,200
feet in length and 0.5 inches wide. In excess of 2,000 lidar backscatter sig-
nals along with individual data blocks and blanking spaces can be recorded on
each tape reel. The tape drive is connected to the lidar's HP 9825A computer
by the IEEE-488-1975 general purpose interface bus which is also an industry-
compatible mechanism. The tape drive is capable of sustained data rates in
excess of 15,000 bits or characters-per-second.
The individual data block, recorded on magnetic tap~ for each and every
lidar backscatter signal is comprised of the following:
. Month, day, year that the lidar shot was recorded
. Time of signal to the nearest second (hour, minute, second)
. Location of data on tape (address)
. Two 32-character identification blocks for each source under-test
. Biomation unit's sampling interval (nanosec/point)
. Video channel identification (linear or logarithmic)
. Location on tape for the reference (clear air) signal or measurement
. Azimuth and elevation angles of the transmitter/receiver's instantaneous
field-of-view with respect to the localized vertical and horizontal axes
. Amount of signal suppression selected by the lidar operator for each of
the two gates, discussed previously.
The cassette tape drive in the lidar computer may be used as an alternate
data recording mechanism. However, each cassette holds only 120 lidar back-
scatter signals on two separate tracks.
The basis for the opacity calculation from lidar A-Scope data is discussed
in Section IV. In this instance, the near-region and the far-region backscatter
signals were used to calculate plume opacity [Equation IV-G]. This represents
an ideal condition.
In the actual field environment, the ideal condition discussed in Section IV,
is rarely encountered. If the lidar were fired into the local atmosphere in any
urban area, the 1/R2 corrected (compensated) signal would not be table-top flat
-------
43
as shown in Figure V-12(a). The signal realistically would exhibit a slight
negative or downhill slope [Figure V-12(b)] which is due to atmospheric at-
tenuation (optical extinction) of the laser beam as it propagates through an
atmospheric path containing ambient particulates and water vapor or humidity.
The magnitude of the atmospheric attenuation increases with lidar range.
The sketch of a lidar return signal through a smoke plume [Figure V-12(c)]
shows that the backscatter signal from the near-region and the far-region also
exhibit the negative slope. Since the signal segments are not horizontally
flat, the opacity calculation would be dependent upon the points along the
signal traces at which the near-region and far-region signal segments are samp-
led or measured by the computer. This range dependence upon the magnitude of
the backscatter signals segments is undesirable.
In the Omega-l Lidar the effects of the signal's negative slope due atmos-
pheric attenuation, are greatly reduced and, much of the time, eliminated by
periodically making a "reference" measurement (clear air signal) along a line-
of-sight near, but not including, the particulate plume under-investigation.
The effects of the non-ideal conditions obtained by the reference measurement
is subtracted from the smoke plume A-Scope signal, in the computer. Thus the
near-region and the far-region signal segments are rendered flat or the range
dependence, mentioned above, has been greatly reduced or eliminated. Likewise
the reference measurement will remove any systematic anomaly in the electronics
of the lidar such as a nonlinearity. (Such an anomaly is usually due to degrad-
ation within a piece of analog electronics or within the detector.) Based upon
past experience, comparison of the processing of lidar data, with and without
the reference shot, has shown that an opacity error of as much as Il to I3% in
actual plume opacity can result by not using the reference measurement, depend-
ing upon the amount of particulate loading along the lidar's line-of-sight.
In order to take the reference measurement [Figure V-12(b)] into account
in the opacity calculation, the computer carries out several functions as follows:
-------
44
Convergence Point
-----.....
(f I at)
Zero Signal
Level
------------------------
Lidar Range Or Time-
(a) Ideal clear air signal, 1/R2 corrected,
(flat)
(negative slope)
(exaggerated)
r r
------------------------
Lidar Range Or Time-
(b) Reference measurement made near the plume in order to account for
the prevailing non-ideal atmospheric conditions, 1/R2 corrected,
(Near Region)
---Plume Spike
(Far Reg ion)
Near Region Pick Interval
\
Far Region Pick Interval
~
1--&-
t
--------
(negative slope)
Signal
}Drop
Due To
Plume
_____1_____1_1______--
Lidar Range Or Time -
(c) Lidar return signal showing the effects of high atmospheric attenuation
upon the near region and far region segments, 1/R2 corrected.
Figure V-12 Sketches Of Lidar A-Scope Backscatter Signals
-------
45
1.
It performs the 1/R2 range correction on both the reference and the
plume data (video) signals. The I/R2 correction mechanism is depic-
ted in Figure V-13. The uncorrected digital signal is comprised of
many short segments or time intervals. The length of these time
intervals, previously called the sample interval, is selected on the
Biomation unit by the operator. The size of the sample interval
(each repetitive time interval) is usually 10 nanoseconds.
Each time interval (t1, t2, ...t ...) in the digital signal beyond
n
or later in time than t is subjected to the 1/R2 correction. The
o
signal amplitude, A , of the nth time interval is multiplied by the
n
square of the time, elapsed from t , defining that interval. In
I 0
Figure V-13, the uncorrected signal amplitude, An' is multiplied by
the square of the time of the nth interval, t , yielding A t 2, the
n n n
corrected amplitude. This process is carried out for each time inter-
val in the backscatter signal producing the I/R2 corrected signal.
2.
It receives the "pick" or "sampling" points either automatically
from the software or as manual commands from the lidar operator,
entered on the computer's keyboard. A pick point is the beginning
of a time (or range) interval which is 100 nanosec (50 ft, 15 m) in
length, which is called a pick interval. Two such pick intervals
must be specified, one in the near-region, I , and one in the far-
n
region, If' of the A-Scope signal [Figure V-12(c)]. These pick in-
tervals are applied to both the reference and the plume data signals.
The criterion for the selection of the pick points is described on
the following examples. Figure V-14 gives 3 actual lidar video return
signals which were computer plotted. Figure V-14(a) is the 1/R2-
corrected clear air reference video signal recorded for use in calcu-
lating the plume opacity from the plume return video signal [Figure
V-14(b)]. These signals contain slight atmospheric backscatter noise
as seen in the ripple or variations in amplitude to the right of the
convergence point. The near-region pick interval, I , is chosen as
n
-------
46
2
A;:~I
-----~------------------
II
II
II
II
II
II
An
..
II
II
II
II
I ,----r-------------
to t, t2 tn=(t-to)
Lidar Range Or Time-
Ant~ < A2 due to atmospheric extinction
R=ctl2, R2 =C2t2 14,
(1/R2)'R2 =
1
c2t2
c2t2 = (1/t2).t2= 1
4
4
Figure V-13 1/R2 Correction Mechanism
-------
47
(Near Region)
(Far Reg ion)
12:10:38
Convergence Po int
J-
Rn
Rf
(a) Reference Signal, 1/R2 Core-ected
12:25:59
Spike
In
If
(b) Plume Data Signal, 1/R2 Corrected
Spike
If
(c) Plume Data Signal. 1/R2 Corrected
NOTES:
(1) Minimum distance from convergence point to the plume spike is
50 meters.
(2) All pick intervals are 100 nanoseconds wide.
(a)
Clear Air Reference Video Signal, 1/R2-Corrected,
pheric noise. This reference signal is for (b).
indicated coincident with In' If'
Lidar-return Video Signal, 1/R2-Corrected, showing slight atmospheric
noise, plume spike and the decrease in atmospheric backscatter signal
level in the far region due to the opacity of the plume encountered.
In' If are chosen as indicated.
Lidar-return Video Signal, 1/R2-Corrected , showing significant atmos-
pheric noise in the near region, plume spike, minimal noise in the far
region and the decrease in far region signal level due to the opacity
of the plume encountered. In' If are chosen as indicated.
showing slight atmos-
Rn' Rf are chosen as
(b)
(c)
Figure V-14.
Computer Plots of Lidar A-Scope Backscatter Signals
-------
48
close to the plume as practicable with the signal quality in the
chosen interval being of minimum overall amplitude and minimal ampli-
tude variation. The reference measurement interval, R , must be
. n
chosen for the same time interval as I , as shown in Figure V-14
n
(a,b).
The far-region pick interval, If' is also chosen as close to the
plume as practicable. The quality of the video signal in this chosen
interval is of minimal amplitude variation and minimum overall ampli-
tude. The far-region reference measurement interval, Rf' must be
chosen over the same interval If [Figure V-14 (a,b)].
Figure V-14(c) is a computer plot of a lidar video signal showing
significant levels of atmospheric backscatter noise in the near region.,
In this case there are only two areas in this region where the pick
interval can be selected, i.e., 1 and 2 as shown. The average signal
amplitude over the 100-nanosec interval in each of these two areas
is the same. However, in applying the above-mentioned criterion
area 2 is the one to be used for the opacity calculation (the respec-
tive reference measurement is not shown). The far-region video signal
amplitude, If' is chosen as shown in Figure V-14(c), according to
the criterion. Any desired pick interval, such as 1 and 2, [Figure
V-14(c)] that is not 100 nanosec wide cannot be used in the opacity
calculation. If no such interval exists in the near-region or the
far-region then the plume data signal cannot be used for the opacity
calculations and is discarded.
Various examples are provided in Figures V-IS through
demonstrate the selection of the best pick intervals.
shows A-scope photos for reference signals and Figures
V-20 are A-scope photos for plume data signals.
V-20, which
Figure V-15
V-16 through
-------
(a) No 1/R2 Correction
49
(b) Photo (a)-1/R2 Corrected
(c) 1/R2 Corrected
(d) 1/R2 Corrected
Figure V-15 Examples Of Pick- Intervals - Reference Signals
(R ectangu lar - Shaped Cu rsors Define Pick Intervals)
-------
(a) No 1/R2 Correction
(c) No 1/R2 Correction
(e) No 1/R2 Correction
50
(b) Photo (a)-1/R2 Corrected
(d) Photo (c)-1/R2 Corrected
(f) Photo (e)-1/R2 Corrected
Figure V-16 Examples Of Pick Inte~vals - Plume Data Signals
(Rectangu I ar-S h aped Cu rsors Define Pick Intervals)
-------
(a) No 1/R2 Correction
(c) No 1/R2 Correction
(e) No 1/R2 Correction
51
(b) Photo (a)-1/R2 Corrected
(d) Photo (c)-1/R2 Corrected
2
(f) Photo (e)-1/R Corrected
Figure V-17 Examples Of Pick Intervals - Plume Data Signals
(Rectangu lar-Shaped Cursors Define Pick Intervals)
-------
(a) No 1/R2 Correction
(c) No 1/R2 Correction
(e) No 1/R2 Correction
52
i.
- ")
I
. \.~: ==1
nil
(b) Photo (a)-1/R2 Corrected
(d) Photo (c)-1/R2 Corrected
(f) Photo (e)-1/R2 Corrected
Figure V-18 Examples Of Pick Intervals - Plume Data Signals
(Rectangular-Shaped Cursors Define Pick Intervals)
-------
(a) Best Near-Region Pick Interval
,.
-?-
vA~ i
~
-
(c) Best Pick Intervals
(e) Best Pick Intervals
53
(b) Best Far-Region Pick Interval
(d) Best Pick Intervals
(f) Best Pick Intervals
Figure V-19 Examples Of Pick Intervals - Plume Data Signals
(Rectan gu lar-Sh aped Cu rsors D efin e Pick Intervals)
-------
(a) Best Pick Intervals
(c) Best Pick Intervals
(e) Best Pick Intervals
54
(b) Best Pick Intervals
-~r
- ,
!
~
~ L ~.
(d) Best Pick Intervals
---r
iy
!
~;
l
(f) Best Pick Intervals)
Figure V-20 Examples Of Pick Intervals - Plume Data Signals
(Rectangu lar-Shaped Cursors Define Pick Intervals)
-------
where:
55
3.
The computer averages the amplitudes of the 10 consecutive time (or
range) sample intervals (each 10 nanosec in length) for each of the
near-region (In) and the far-region (If) signal segments within the
plume data signal. It also calculates the standard deviation of
these 10 data points for In and If'
4.
The computer calculates the average of the amplitudes of the 10 con-
secutive time sample intervals for each of the near-region (R ) and
n
the far-region (Rf) signal segments within the reference signal.
The R . Rf intervals are chosen for the same pick intervals as I
n n
and If [Figure V-14(a.b)]. The standard deviation of the 10 data
points for each respective Rn and Rf is also calculated.
The actual opacity calculation is derived from the information
given in Figure V-12. The near-region and far-region signal segment
measurements are related by:
In = kRn
If' = kRf
(V-la)
(V-lb)
I = near-region signal amplitude. plume data signal.
n
If'= clear air equivalent signal amplitude [Figure V-12(c)].
far-region.
R = near-region signal amplitude. reference signal.
n
Rf = far-region signal amplitude. reference signal.
k = a proportionality factor.
The opacity measurement is related to the signal drop due to the plume
[Figure V-12(c)]. and it is derived in the following manner:
Op = 100%
[ 1 - C:,t ]
(V-2)
-------
56
Substituting Eq (V-lb) for If" Equation (V-2) becomes:
Op = 100%
[ 1 - V~J ~ ]
(V-3)
Using the relationship k = I /R , (Eq (V-1a), in Eq (V-3», the propor-
n n
tionality factor is eliminated, which gives:
o = 100%
p
[ 1 - (~; ~: t ]
(V-4)
This expression, which takes a reference (clear air) measurement into
account, is the one used in the Omega-l Lidar's computer program to calculate
plume opacity.
Eq V-4 is directly applicable to data obtained and recorded through the
lidar's linear channel.
If the lidar data were originally obtained and recorded
mic channel, then it must be mathematically transformed back
before it can be processed further.
using the logarith-
into linear form
The transfer function for the logarithmic amplifier was carefully and
accurately measured before being incorporated into the computer program. The
logarithmic amplifier output, V t' is related to the input signal, V . , by:
ou ln
V t = 0.04 log V. + 0.18
ou 1 n
(V-5)
The Biomation unit digitizes the output signal of the logarithmic channel
to a digital count value (8 bit binary value, base 10) over the interval from
o to 255. The magnitude of this range is dependent on the Biomation unit's
input voltage scale selected by the lidar operator. Based on the consideration
of the average operative parameters or levels of the Omega-l lidar's electronics,
this input scale is usually 0.2 volts full scale (IO.1 V). Therefore, the
digital count or binary value (C) is related to the Biomation's input voltage
by (256 total counts, 0 to 255).
C = 256
0.2
(digitizer counts) = 1280 (counts/volt)
volts
-------
57
By using the logarithmic amplifier transfer function (Eq V-5), this yields
the following:
C = 1280 V t
ou
= 1280 (0.04 log V.
ln
C = 51.2 log V. + 230
ln
+ O. 18)
(V-6)
For use in the computer program, the inverse logarithmic transform is
required. Therefore Eq V-6 is solved for V. as follows:
ln
log V. = C-230
1 n 51. 2
and taking the antilog of both sides of this equation,
V. = 10 (C-230)/51.2
ln
and simplifying,
V. = 10 (1/51.2)(C-230)
ln
= 1. 046(C-230)
"= 1.046C x 1.046-230
V. = 3 x 10-5 (1.046)C
ln
(V-7)
The constant value of 1.046 is for 0.2 volts (full scale) or !0.1 V input scale.
For other input scale values the constant value is given as follows:
Table V-4
LOGARITHMIC CHANNEL CONSTANTS
Input Voltage Scale (Volts)
Value of Constant
+ 0.1
:;: 0.2
:;: 0.5
1.046
1.094
1.252
-------
58
Once the inverse transformation has
data, then the opacity equation (Eq V-4)
plume opacity as discussed previously in
been applied to the logarithmic channel
is used by the computer to calculate
this section.
The flow of the digital lidar data under control of the computer is illus-
trated in ~igure V-2I. The analog video signals, coming from either the linear
or logarithmic channels, are converted into digital form in the Biomation Fast
Transient Recorder, and sent to the computer. The data flows in essentially
straight-line fashion with several alternate paths as shown by the straight
line and branch arrows [Figure V-2I]. These paths may be selected by the lidar
operator when the computer program is executed. The function of each of the
blocks shown in the diagram is explained in the following paragraphs.
Regarding data acquisition, the lidar return data is read from the Bioma-
tion unit or from the magnetic tape into the computer memory. If the data
were read from the Biomation, it may be optionally recorded on tape as well.
At the point of normalization, any DC bias which the data may have is
removed. This is accomplished by calculating the amount of offset required to
bring the zero-signal-level part of the return video signal [Figure V-II] to
true zero. The offset is then subtracted from the data during subsequent calcu-
lations. The input signal offset is manually adjustable on the Biomation unit.
Scaling is performed after each subsequent computational step such that
the numerical value of the data will remain in the range of 0 to 255 digital
counts (arbitrary units). This is done for the convenience of data display
(plotting, printing) and has no effect on the calculation of opacity.
Following the data flow sequence [Figure V-2I]. the logarithmic amplifier
transform is completed, if necessary, and the compensation for the video signal
gating (two gates), selected by the lidar operator, is carried out as required.
2
The I/R -correction or compensation is carried out as required [Figure V-8
and V-g].
-------
wrfJ:10
OR
normalization
OR
log amp
transform
OR
gating
compensation
Figure V-21 Omega-1 Lidar:
59
OR
(range) -2
compensation
OR
data
listing
opacity
calculation
standard
deviation
calculation
results
printout
Digital Data Flow Diagram
-------
60
The digital data, stored in the computer, can be listed in numerical tab-
ular form as time in 10 nanosec increments (Biomation sample interval) along
with the corresponding digital count value. The 1idar operator can select the
time interval over which the data is listed. At this time in the data flow
sequence, a two-dimensional plot of the 1inear/ transformed, uncompensated/
compensated data can be made.
The opacity calculation is now completed in the manner previously discus-
sed. The most recent reference measurement is used in the calculation, Eq V-4.
If no reference measurement is used then a value of 1 is assigned to the ratio
Rn/Rf in the equation. Prior to executing the program the 1idar operator enters
the two IIpickli intervals (via computer keyboard) which are the data sampling
time intervals (100 nanosec in length) for both the near-region and the far-
region of the plume under investigation. These intervals are determined by
the location of the plume in the time domain (or range where the round-trip
range = speed of light. time/2) and by the atmospheric conditions along the
1idar's 1ine-of-sight through the plume, as judged by the operator. The program
calculates average values for Rn' Rf' In and If [Figure V-12] beginning at the
respective pick-time point (word) and continuing for the next nine intervals
for a total of 10 consecutive intervals (100 nanosec) resulting in a 10-point
average amplitude over the interval for each R and I. The standard deviations
(SRn' SRf' SIn' SIf) for the Rn' Rf' In and If average values respectively,
are calculated at this point for use in the next step.
The standard deviation, S , of the calculated opacity, 0 , is obtained by
o p
a multi-variable function which is given in terms of the standard deviation of
the individual variables. Given Eq V-4 for opacity and the standard deviations
previously calculated, the standard deviation of the opacity value is calculated
using:
\ = [ (: ~~ r
S 2 +(~)2 S 2 +(~)2
Rn a R Rf a I
f . n
+(~) 2 S 2]~
a I If
f
S 2
In
(V-B)
-------
61
where:
S = standard deviation of the opacity value, 0 .
o. p
ao laR = partial derivative of the opacity function [Equation (V-4)]
p n
with respect to the clear-air reference signal variable in the near-
region [Figure V-14].
SRn = standard deviation of the pick-interval segments for the clean-
air reference signal in the near-region.
aOp/aRf = partial derivative of the opacity function with respect to
the clear-air reference signal variable in the far-region.
SRf = standard derivation of the pick-interval segments for the clear-
air reference signal in the far-region.
ao lal = partial derivative of the opacity function with respect to
p n
the plume backscatter signal variable in the near-region.
SIn = standard deviation of the pick-interval segments for the plume
backscatter signal in the near-region.
aOp/alf = partial derivative of the opacity function with respect to
the plume backscatter signal variable in the far-region.
Slf = standard deviation of the pick-interval segments for the plume
backscatter'signal in the far-region.
The largest and most significant source of error is 0 is due to the atmos-
p
pheric inhomogeneities along the lidar's line-of-sight resulting in
noise. The standard deviation S is an indication of the magnitude
o
signal noise within the near-region and far-region pick intervals
calculation of 0 .
P
video signal
of the
atmospheric
used in the
The final printout consists of the following parameters:
. Month, date, year of the lidar signal,
. Individual file address of lidar signal on the magnetic tapes,
. Average value of In' If' Rn' Rf'
. Standard deviation for In' If' Rn' Rf'
. Opacity value, 0 ,
p
. Standard deviation, S .
o
-------
62
During the execution of the opacity calculation, the computer is program-
med to inspect the variability of the near-region and the far-region signal
segments, and the value of S. If the standard deviation of S is greater
o 0
than 8% the computer prints an error indication immediately after the opacity
value is printed. This form of an acceptance/rejection criterion [see Section
VIII for detailed discussion] is carried out for each lidar signal analyzed.
If a negative opacity value is calculated, which means that the backscatter
amplitude in the far-region (behind the plume) is greater than that in the
near-region, usually due to fumigation from a neighboring source, the computer
also prints an error indication.
If the wrong reference measurement is being used to normalize a given set
of A-scope data, then a IIWrong-Refli indication is printed on the paper printer
immediately after the opacity value.
The lidar data, recorded on magnetic tape, is also processed at NEIC on
the PDP-11-70 computer which is much faster than the lidar1s computer. The
same program elements are used on the larger computer.
The temporal plume opacity values for a given source, and associated stan-
dard deviations, are plotted in a two-dimensional format along with the appli-
cable opacity regulation. An example of such a plot is given in Figure V-22.
The vertical bars represent ~l standard deviation calculated for each respec-
tive opacity value.
The computer also calculates and plots running averages of the opacity
value data. The length of the time period of the running average is defined
by a particular state air regulation. A running average is defined in the
fo 11 owi ng way:
If i opacity values, from M to N, have been averaged over a given time
interval, the running average is performed by successively subtracting the Mth
value and adding the N+l value and calculating the average for the i opacity
-------
11 ~l1
w <-
Ol'-1EGR
ID~
911
LEGEND
83
10
Calclllated - I
Opacity
t :t One Standard
) Devialion
. 611
>-
t-
-SI1
v
a:
n..
°Lia
~
II 1111 .
- . tIIC~t;mUl
30
20
1'1 I
111
opacity limit. Okiahoma
11
JI'111111
r-rrn1
"~'2S 'liB
LOCAL TIME
-10
12'2B' iH~
LIDAR OPACITY MEASUREMENTS - CO BOILER STACK
Figure V-22 Two-Dimensional Plot Of Omega-1 Lidar Opacity Data
('"")
a
:z
-i
......
::z:
c
rr1
o
a
::z:
::z:
rT1
><
-i
-0
:to>
G1
rr1
12'3il'BB
m
w
-------
64
values again, then subtract M+l and add N+2 and perform the calculation again,
etc. The number of values averaged in this manner is always i.
The advantage of this technique is to continually have available the aver-
age opacity of a given source over a running 5 or 6 minute period usually ap-
pearing in state air regulations.
The Omega-l Lidar can fire the laser, collect the return signal and record
the resultant A-scope video signal on magnetic tape once every second, maximum
rate. If an opacity value is calculated for each lidar signal, then the data
rate is lengthened to about one measurement every 2 seconds. The data rate is
continuously variable from one signal-per-second to a single signal, the time
of which is at the will of the lidar operator.
The lidar is mounted in an enclosed metal-lined van which is in turn
mounted on a 1977 Ford C600 truck [Figures V-23 and V-24]. The van has three
separate rooms: a) laser room, b) computer room, and c) the generator room.
The laser and computer rooms are equipped with heaters and air conditioners
providing environmental control for year-round operation.
There are two electrical generators mounted in the generator room which
is across the front of the van [Figure V-25]. The upper-level generator sup-
plies regulated 110-120 VAC power to the system's electronics. The internal
lighting systems are also powered from this unit. The large generator (30 KVA)
supplies electrical power to the laser (18 KVA) power supplies, the water refrig-
eration unit and the air conditioning systems.
The doors in the rear of the van open so as to provide a clear or unobstruc-
ted pointing position anywhere in the solid angle of f95° in azimuth about the
horizontal longitudinal axis of the van (1800 total azimuth) and of -100 to
+900 in elevation about the same axis. From the time the truck is stopped at
-------
---
- - ----
a
0"1
01
Figure V-23 Omega-1
Mobile
Lidar System:
View Of Right Side
-------
".
---... - ----~
a
r--
~
t
Ef
-<"'"
~....~
-
---
Figure V-24 Omega-1 Mobile Lidar System:
View Of Left Side
'"
'"
-------
67
,
..
1.11
/
I
f'
\
~
Figure V-25 Omega-1 Lidar:
Generator Room
-------
68
a given monitoring site. the lidar is in full operation in less than 10 minutes
day or night. The lidar is quickly and easily aimed at a smoke plume in question
by either direct viewing through the Celestron telescope or through an aiming
(rifle) scope on the lidar pedestal and bore-sighted to the Celstron telescope.
There is also a small door in the top of the van. at the back as shown in
Figure V-26. that provides a vertical line-of-sight for the lidar. The lidar
can be operated through this door with the vehicle standing or in motion. This
arrangement permits the spatial or temporal monitoring of:
a) plume drift and dispersion characterisitics/dynamics.
b) plume behaviour such as fumigation. coning. etc..
c) location and movement of the combining of plumes.
d) plume density variations.
e) vertical burden and inversion layers
to name a few. These modes in addition to the remote measurement of plume
opacity can be conducted during either day- or nighttime hours. (The lidar
receiver is solar-blind; however. it cannot be aimed directly into the sun.)
The data collected during these modes of operation are analyzed on the NEIC
Laboratory Computer and the results plotted on the two-dimensional plotter in
a variety of formats.
The l,dar mechanism is not effective for plume opacity monitoring during
heavy rain storms. snow storms and fog conditions.
-------
Vertical Port
. .
...........
C'\
1..0
Figure V-26 Omega-1 Lidar:
Rear View
-------
VI.
PERFORMANCE EVALUATION AND THE CALIBRATION MECHANISM
OF THE OMEGA-l LIDAR
During the time that the Contractor was fabricating the Omega-l Lidar and
even after it was accepted, EPA technical personnel, with the advice 'and counsel
of lidar specialists from two separate EPA contractors, formulated a detailed
performance evaluation program and formulated the design necessary for an effec-
tive calibration mechanism.
The performance evaluation tests were not designed for proof-of-principle
of the lidar technique a mechanism which had been done several years prior.4,21
These historical tests, performed with two different lidars (EPA-RTP Lidar and
the SRI Mark 9 Lidar) having ruby lasers as optical transmitters, have clearly
established the validity of the lidar mechanism, and produced technical/logistic
information that was used extensively in the design of the Omega-l Lidar which
is an optimum system for field use in the measurement of plume opacity. The
performance evaluation tests were designed to fully wring-out the performance
parameters and characteristics of the Omega-l Lidar, revealing any anomalies
that might have been present.
EPA technical personnel judged the following tests as the necessary and
sufficient tests to demonstrate that the Omega-l Lidar measures the opacity of
visible particulate emissions with consistently high accuracy:
a)
Aerosol Chamber Tests - A technical investigation revealed
that the SRI/EPA aerosol chamber, previously established and operated
as a simulator for particulate plumes, provided a realistic outdoor
laboratory environment for establishing and evaluating the performance/
response characteristics of lidar systems for smoke plume opacity mea-
surements. The aerosols used to generate the smoke plumes were fly
ash and iron oxide particulates whi'ch' were"charactertzed-by part'icle-
size distribution cl~sses or ranges.
-------
71
The lidar performance tests. conducted using the aerosol chamber as
the simulated smoke plume. were preliminary tests or first-run tests
for the purpose of establishing the base-line performance of the
Omega-l Lidar and the uncovering of the anomalies that were found in
the system.
b)
Internal Calibration Mechanism - In order to establish the validity
of the visible emissions opacity data obtained with the Omega-l Lidar.
a rather simple mechanism was formulated and designed for testing
the lidar system performance in the field under conditions. as nearly
as possible. identical to those encountered during actual plume mea-
surements. This test is a demonstration of the accuracy of the lidar
opacity measurement which depends on the verification of the proper
operation. linearity* and repeatability in performance of all the
electronics in the lidar receiver from the photomultiplier tube (PMT)
detector through the computer. This test. which requires from 1 to
3 minutes to perform. serves as a calibration mechanism for the proof-
of-proper-operation requirements of the evidentiary chain employed
in the EPA enforcement activities. This test is performed for discrete
opacity values ranging from 0% through approximately 80%.
c)
PMT Evaluation Tests - The PMT detector is the key component in the
lidar receiver. The EPA-RTP lidar encountered a problem with after-
pulsing with that sytems's PMT. (Afterpulsing. also called signal-
induced noise, is defined as the departure of the output electronic
signal of the PMT from the predicted or expected values immediately
after an encounter with a strong optical signal. The strong optical
signal is the backscatter signal from the smoke plume under test and
the afterpulsing occurs in far region portion of the video signal
just beyond the plume.
* Linearity is defined by the equation y = mx + b. For a given change in x
there is a corresponding proportional change in y. The proportionability
factor m is not a function of x or y but is a constant. x is the input sig-
nal amplitude, y is the output signal amplitude, m is the slope of straight
line and b is the intercept point where the line crosses the y axis of a two
dimensional graph.
-------
72
The Omega-l Lidar's PMT (ITT 4084) is of special design. The design
of this detector was based on the results obtained through research
with the EPA-RTP Lidar which has eliminated the after-pulsing problem.
During the time just prior to the aerosol chamber tests SRI Interna-
tional conducted numerous tests on the Omega-l Lidars's PMT. These
tests showed that there were no after-pulsing effects in this PMT.
The PMT performance tests are repeated periodically, at least every
6 months, to verify that the tube performance characteristics have
not changed. Additional tests performed on this PMT are to be given
later in this section.
d)
Field Experimentation Tests - The field tests have been used exten-
sively for studying the correlation between the lidar-measured opac-
ity values and the respective in-stack transmissometer opacity values.
The tests have been used to train lidar operators, and to optimize
the operation and performance of the lidar system such as the computer
software used in internal data management and recording. The data
recorded during these tests has been analyzed and documented in a
systematic data base for future reference/use. These tests are on-
going at the present time and will be carried out for years to come.
More detailed information and test results are given in the remainder
of the section of the report.
AEROSOL CHAMBER TESTS
These outdoor laboratory tests were conducted at the facilities of SRI
International (Standard Research Institute) in Menlo Park, California. (Refer
to Section III for background information.)
The test site or range consisted of a vacant lot of ground, an aerosol
chamber10'28 9.75 meters (32 ft) in length and a back-stop for the laser beam,
as shown in Figure VI-l. The overall length of the optical path (lidar to
-------
73
\
Exhaust
BLACK TARGET
.....t)I
......~ --
...... 0' -----.
....... 3'00
.:.----
Dust feeder
Figure VI-1
DIAGRAM OF EXPERIMENTAL SYSTEM 28
-------
74
back-stop) through the aerosol chamber was 281 meters (922 ft). The aerosol
chamber is a device used to simulate actual particulate plumes with a high
degree of laboratory control over the applicable parameterst especially plume
opacity. The simulation of a plume is accomplished by feeding submicron-to-10
micron size particulates (size selectable) into the aerosol chamber by a parti-
cle feeder and a high volume (5800 ft3/m(cfm)) blower or fan [Figure VI-2].
The particulates are metered into the air stream by the groove and disk feeder
[Figure VI-l]. The particulate-laden air stream is highly controlled from the
feeder through the aerosol chamber into the sighting tunnel which has an effec-
tive path length of 9.1 meters (30 ft). It is decelerated in an expanding
duct network before entering the sighting tunnel. The particulates do not
escape from the sighting tunnel through the sighting ports because an aerosol
curtain is used to establish and maintain a fixed boundary to the particulate-
laden air through which the lidar can sight without affecting the transmission
of the laser energy. The particulate-laden air escapes the chamber through
the exhaust ports on top [Figure VI-l] away from the lidar's line-of-sight
through the sighting tunnel. The effective plume opacity is controlled directly
by the density of the particulate-laden air within the sighting tunnel.
Since plume opacity is defined as one minus plume optical transmittance,
an optical transmissometer was incorporated into the aerosol chamber's sighting
tunnel in order to continually monitor the optical transmittance of the particu-
late-laden air over the 9.1 meter effective path length through the sighting
tunnel. The transmissometer was a photoptic response white-light transmissometer
directed along the sighting tunnel as shown in Figure VI-2. The source, a
tungsten filament lamp, was located at one end of the sighting tunnel while
the optical detector, a silicon detector, was located at the other end. The
transmissometer's receiver was equipped with a special optical filter in order
to approximate the response of the human eye, since visible emissions observa-
tions are collected by human observers (Reference Method 9). This transmisso-
meter had an integration time constant of about 0.25 sec., indicating that it
could monitor any moderate opacity changes rapidly and effectively. The trans-
missometers in the 40 CFR Part 60 smoke generators have a white-light source
and a time constant of 5 seconds or less, [Table 9-1, Reference Method 9 (see
Field Experiment section)].
-------
75
EXHAUST AIR
TO ATMOSPHERE
SOUTHEAST
SlOE
_NORTHWEST SlOE
OPEN ENOS 120" . 20'"
(a) elEVATION
EXHAUST
-,~j[f ~11
~ AEROSOL
C.OLLIMATED I CURTAIN ATMOSPHERIC
LIGHT BEAM~~ ~th = "t -- - - - = = = = = - - - S::I: ~NNE~""" ./ ~,tvIR
/ 11- 201 ~~ ~ - - - - = -= -= -=- -=- -=- -l~ro-OPTICAL
~ .......-f'll... . l- 34"-J 10" } DETEt;TOR
3" I 36" 55 1 1/0" HOLES --JI-,- - :;-/- T ~
12""- I--- r
--- PLENUM CHAMBER
I.
32'
~I
(b) SECTIONAL VIEW OF AEROSOL SIGHTING CHAMBER (Section B-BI
Figure VI-2 AEROSOL CHAMBER DETAILS28
-------
76
Calibration tests performed on this transmissometer showed it to respond
in a linear manner (to within 1% transmittance) to neutral density (shades of
gray) optical filters placed in its beam path. Its calibration was checked
just prior to the start of each lidar-chamber data run. The opacity values of
the particulate-laden air were recorded on a continuous strip-chart recorder
and on a digital printer which was activated by a signal from the lidar when
the laser was fired through the sighting tunnel.
The particulates used during these tests were four size fractions of fly-
ash and one of iron oxide. The four size fractions (particulate diameters) of
flyash were: 1) 0.1 to 10 microns, 2) 0.1 to 2.5 microns, 3) 2.5 to 5 microns
and 4) 5 to 10 microns. The lidar and the chamber transmissometer measured
the plume opacity for all the above-mentioned size fractions.
The performance evaluation tests were performed during a 4-week period.
Prior to recording actual lidar data through the aerosol chamber, tests were
conducted in order to establish the proper operating signal levels of the Omega-l
Lidar1s photomultiplier (PMT) detector, linear and logarithmic channels and
the Biomation 8100 Fast Transient Recorder (digitizer).* The new internal
calibration mechanism (discussed later in this section of the report) was in-
stalled, and was used extensively in these tests. Once these tests were satis-
factorily completed, the lidar was then aimed and fired down the test range
through the sighting tunnel of the aerosol chamber [Figure VI-l]. A photograph
of the aerosol chamber is shown in Figure VI-3.
Two additional problems were encountered within the lidar. One problem
involved the electronic signal interference in the lidar receiver caused by
the Pockel Cell Q-Switch in the laser. This interference is called electromag-
netic interference (EMI). This problem was solved by rerouting the electronic
signal (video) cable, from the PMT detector to the processing electronics,
away from the Q-Switch power supply and remote control cables. Also an addi-
tional electronic shield was put on the electronic signal cable and grounded
* At this time the Biomation digitizer was taken to the Biomation factory
for complete calibration.
-------
77
Figure VI-3 SRI International Aerosol Test Chamber Facility
(As Viewed From The Lidar End)
-------
78
or terminated at both ends. The high voltage cables from the Q-Switch power
supply to the Q-Switch, located within the laser invar rails, were twisted and
additional shielding installed with proper termination. Diagnostic tests were
then performed revealing that the EMI noise problems were greatly reduced to
an acceptable level.
As viewed on the oscilloscope display this EMI noise was barely visible
in the receiver's inherent electronic noise level that is always present in
the time interval from the time the receiver was effectively turned-on to the
time the laser was fired; it had no effect upon the higher amplitude signals
used in the opacity calculation.
The second problem mentioned above involved the beam pattern out of the
Holobeam (Model 624) laser's upcollimating telescope, which is a beam-shaping
device. It had a noticeable amount of energy in the first secondary maximum
surrounding the intense central spot or primary maximum. The presence of this
effect was evident in the large laser energy reflection signal from the front
surface of the aerosol chamber as recorded and observed on the oscilloscope
display. The entire optical train (all optical elements along the laser's
invar rails) was reali~ned including the upcollimator. This problem had no
effect upon the opacity measurements of the particulate plume within the aerosol
chamber [see Section V for signal processing details], however, it did produce
a larger return signal than normal from the chamber structure. It was decided
at that time that the upcollimator would have to be changed, reworked as required
and refocused for proper performance (beam shape) in the NEIC Optics Labora-
tory in Denver.
The Omega-l Lidar tests using the aerosol chamber were divided into runs.
Each run consisted of a sequence of ten lidar measurements while the aerosol
chamber was operated at a particular (predetermined) opacity value with as
nearly uniform particulate concentration as was really possible to maintain.
While the chamber was in operation, the opacity was monitored continuously by
the filtered white-light transmissometer as previously discussed in this sec-
tion. Each time the lidar was fired, an electronic signal was transmitted to
the aerosol chamber which activated the digital printer recording the following
information:
-------
79
. Time of each firing to the nearest second,
. Transmissometer opacity output value,
. Ambient temperature,
. Electrical power to the transmissometer white-light lamp.
Constant telephone communications were provided between the lead-operator
of the Omega-l Lidar and the technician in the control room of the aerosol
chamber. The technician told the lidar operator when to begin a data run which
was predicated upOh the stability of the opacity of the particulates within
the chamber. The lidar operator would initiate the data run and would continue
only if the local atmospheric path along the test range was reasonably stable.
Inhomogeneities along this path were caused by small wind gusts blowing ground
dust through the area. This occurred in the afternoon hours; so most of the
tests were performed from early morning until noon when the air along the range
or path was calmest.
A total of 43 data runs were performed with the aerosol chamber opacity
values discretely ranging from 0% to greater than 90%. Of these 43 data runs,
13 were discarded and not used because of fugitive dust interference within
the lidar's line-of-sight through the aerosol chamber test range.
The data obtained during the 30 acceptable data runs (251 data values,
49 data values were discarded due to excessive interference of fugitive dust)
were processed with the Omega-l Lidar computer and the software that has been
written, developed, verified and documented for field enforcement use [see
Section V].
SRI performed an analysis of the comparison of the transmissometer's opa-
city output data recorded by the continuous strip-chart recorder and the digital
printer. Out of the entire data set, only 12 data values or points displayed
an absolute opacity difference of 5% or greater from one recorder to the other.
In order to summarize and graphically plot the Omega-l Lidar opacity data
in correlation with that of the aerosol chamber1s digital output printer, it
was stipulated that the nominal opacity value of the printer would serve as the
-------
80
basis rather than the strip-chart recorder. Each 1idar opacity value was plot-
ted against the respective printer value. All the data points were plotted
which included all opacity values from 0 to 90% for both particle constituencies
(fly ash and iron oxide). the 1idar's linear channel output. the logarithmic
channel output. 1idar data corrected for clear-air atmospheric effects and the
data that was not clear-air corrected. The data were p1otted28 with the printer
opacity along the abscissa and the 1idar opacity along the ordinate of the
graph. With the shape of the graph being square. the plotted points were gath-
ered along a diagonal line making an angle of 45° from the abscissa [Figure
VI-4]. This graph did not take into account any error in the printer output
values or the 5% difference between the printer opacity value and the strip-
chart recorder value.
A frequency distribution of the differences between the 1idar opacity
values and the corresponding printer opacity values for all the 251 data points
was plotted [Figure VI-5]. The distribution was a normal distribution function.
The standard deviation of this distribution (all 251 data points) was calculated
to be about 6%. Therefore, according to this data processing mechanism. the
measurement accuracy of the lidar for single measurements of opacity is about
t 6% with a 68% confidence limit and about t 12% with a 95% confidence limit.
The probable error calculated from this distribution is about 4%; i.e.. a single
lidar measurement in this group of data has a 50% confidence of being within t
4% of the actual value.
As was stated above. the printer opacity value was assumed to be the basis
for the graphic plots and calculations; i.e.. there was no accounting for the
inherent error in the aerosol chamber's transmissometer and recording equipment.
However, there is an error associated with this facility and its measurement
of the opacity of the particulates dispersed within the sighting tunnel of the
aerosol chamber. In order to see this more clearly. the lidar opacity data
and aerosol chamber opacity data for four data runs are included in Table
VI-I. The far-right column in this table is the standard deviation of the
measurement of the opacity value as calculated by the 1idar computer from the
-------
81
100
c
'"
~
'"
Co
60
,
,
,
,
+ +~,,'
.& ,,'
,
+ 0 "
+ '
+ ~'o
~o ,
0°0 " +
o '
+ 0 "
Q.o~,'
~,' 0
" 0
00.. ' +
£t,~ +
, ~
+ " ~ 00
o ~~+ 00
.. * .,'" '. 0
.0 ~ p~ ;
~ '
. .0 ~-;:J'f .
+$ ~ .,' .+
+ -~ ' ~ +
Y \f +
00 ~ ' +
o ,
,+
:+ ,9;
O~~~;O~ 0
0, ~tp
" 010+ 0
+
80
I
>-
to-
G
«
D.
o
CI:
«
o
:J
+
40
o
o
20
o
o
20
40
60
80
100
CHAMBER OPACITY (PRINTER) - percent
Figure VI-4 LlDAR-DERIVED OPACITY VALUES PLOTTED AGAINST CORRESPONDING
TRANSMISSOMETER-OBSERVED OPACITY VALUES 28
The two symbols represent two different methods of obtaining opacity values
from the lidar signature: 0 based on a reference signature (clean air chamber)
and + computed without reference signature (clean air before chamber) -
see Appendix B for detail.
-------
25
ALL POINTS
IJ a
DATA 0.29 6.37
20 6.27
MODEL 0.63
...
15 .' ,
~ ,
OJ ...
.c \
E
:J
C
I
>- ,
U ,
Z ,
w 10
::)
a '
w ,
cr
u. \
\
\
, \
, \
,
5 ...
, \
, \
,
o
--20
-15
-10
-5
o
5
10
15
20
25
OPACITY DIFFERENCE (UDAR - PRINTER) - percent
Figure VI-5 FREOUENCY DISTRIBUTION AND BEST-FIT NORMAL DISTRIBUTION FOR THE DIFFERENCE IN LIDAR
AND TRANSMISSOMETER-MEASURED OPACITIES (all observations)28
co
I\)
-------
83
TABLE VI-l
DATA SAMPLE
Run Shot Printer Opacity Lidar Opacity Li da r Opaci ty
No. No. in % in % Standard Deviation(a)
13 0 59. 1 57.0a 1.0
13 1 57.5 54.0 2.0
13 2 57.2 60.0 2.0
13 3 63.7 66.0 2.0
13 4 61. 8 59.0 2.0
13 5 59.0 54.0 1.0
13 6 64.7 61. 0 2.0
13 7 58.2 53.0 1.0
13 9" 55.6 49.0 1.0
16 0 41. 5 40.0a 2.0
16 1 41. 1 38.0 2.0
16 2 45.4 46.0 2.0
16 3 43.2 33.0 2.0
16 4 44.1 30.0 7.0c
16 5 46.9 26.0 2.0
16 6 47.6 29.0 3.0
16 7 42.1 32.0 3.0
16 8 40.5 44.0 3.0
16 9 45.8 46.0 2.0
10 0 67.3 74.0b 3.0
10 1 77.3 79.0 3.0
10 2 67.9 70.0 3.0
10 3 63.4 69.0 3.0
10 4 79.4 84.0 3.0
10 5 76.4 79.0 3.0
10 6 72.7 75.0 3.0
10 7 70.7 76.0 3.0
10 8 76.4 79.0 2.0
10 9 66.3 69.0 3.0
11 0 55.7 59.0b 4.0c
11 1 68.9 72.0 3.0
11 2 74.6 78.0 3.0
11 3 72.1 78.0 2.0
11 4 83.8 88.0 2.0
11 5 79.9 81. 0 2.0
11 6 68.7 75.0 5.0
11 7 72.1 78.0 2.0
11 8 82.6 79.0 8.0c
11 9 73.5 66.0 7.0c
a Data corrected for atmospheric (clear air) effects in the lidar computer.
b Data not corrected for atmospheric effects in the lidar computer.
c Large a due to fugitive dust along the lidar's line-of-sight.
-------
84
original data collected by the lidar receiver. This gives an indication of
the integrity of the lidar return or backscatter signal from the test range.
For example, in Run #13-shot 0, the lidar measured and calculated the
aerosol chamber opacity to be 57% with a standard deviation of 1% (the transmis-
someter measured the opacity to be about 59%). This says that the opacity of
the particulates in the aerosol chamber was 57% ! 1% with 68% confidence limits,
57% to + 2% with 95% confidence limits and 57 + 3% with 99% confidence limits.
Run #10, Shot 9, was 69% with a standard deviation of 3%. The latter half of
the data in Table VI-1 displays a somewhat larger standard deviation because
the effects of the local atmosphere along the test range were not subtracted
out as they were in the first half. This left the atmospheric noise in the
calculations of the last half.
The quality and integrity of all the lidar-measured opacity data were
reviewed in detail for any errors in calculation, choice of pick points [s~e
(
Section VJ, and recording of each opacity value in a tabular format. No errors
were present. Then the overall standard deviation of the lidar data for all
251 data points was 3.1% as calculated by the lidar computer. The mean differ-
ence between the lidar and the respective chamber-opacity values was 0.3%.
The results of the aerosol chamber tests indicate that the overall standard
deviation was about 6%. The difference between these two values lies within
the assumption or stipulation that the printer output of opacity was an abso-
lute basis (opacity value with no associated error) for the entire series of
calculations. The errors in the transmissometer's measurement must be taken
into account. The inability of the transmi.ssometer to respond to rapid changes
(inhomogeneities and particulate kinetics) in actual chamber opacity values
must also be considered. The integration time for the transmissometer is
about 0.25 seconds. The lidar measured the opacity of the particulates in the
sighting tunnel in about 30 nanoseconds; i.e., 30 x 10-9 sec, which is 8.3
million times shorter. The transmissometer did not measure opacity along pre-
cisely the same path as did the lidar, which is a physical constraint that
couldn't be practically removed or eliminated. So the standard deviation,
-------
85
that may be attributed to the other sources of error, was calculated using the
overall standard deviation of 6%, the lidar standard deviation of 3.1% and the
fact that the square of the total standard deviation equals the sum of the
squares of the lidar standard deviation and the other-error standard deviation
(cr 2 = cr 2 + cr 2). The cr may be calculated with the expression cr = (cr 2 -
01 l E:. E:. g 0
cr 2)~. Thus, cr = 6%, cr = 3.1% and cr = 5%. The standard deviation of the
l 0 l E:.
other errors, given above, is 5%. Thus, if the true opacity in the aerosol
chamber's sighting tunnel were 50% (for example), then the output value printed
on the digital printer would have a 68% confidence limit of being in the inter-
val of 50 f 5% and a 95% confidence limit of 50 f 10%. The lidar measured
opacity value would have a 68% confidence limit of being 50 f 3% and a 95%
confidence limit of 50 f 6%.
INTERNAL CALIBRATION MECHANISM FOR THE OMEGA-l LIOAR
In order to establish the validity of the particulate plume opacity data
obtained with the Omega-l Lidar, an internal calibration mechanism was designed,
fabricated and installed in the lidar's receiver. It is used for testing the
overall system performance in the field under conditions, as practicable, iden-
tical to those encountered during real plume measurements. The validity of
the lidar opacity data (in enforcement especially) is dependent upon verifica-
tion that the system was performing as intended at the time the measurements
were made. This mechanism evaluates the performance of the lidar receiver
independent of the laser transmitter.
The internal calibration mechanism has been named an optical signal genera-
tor or optical generator [Figure VI-6]29. The optical generator uses a highly
controlled small solid-state laser (galium aluminum arsenide) and light-emitting
diodes (LEO) to inject an optical signal through two fiber optic cables into
the receiver ahead of the PMT detector as depicted in Figures VI-7 and VI-8.29
The two LEOls in the optical generator simulate two functions which are the
fo 11 owi ng:
-------
-- - - - --
- -------
M
"""
.-.
",'j
»~
~
F igu re VI-6 LlDAR OPTICAL PULSE GENERATOR (control unit and two light sources shown coupled to EPA!NEIC PMT
assembly) 29
co
0"1
-------
II EXT TRIG IN
I MANUAL TRIG
IPLUME AMPL ADJI
son
TIMING
CIRCUITS
PULSE
GENERATOR
I PLUME RANGE ADJ I
I SLOPE ADJ I
I AMPLITUDE ADJ I
I OFFSET ADJ I
EXPONENTIAL
WAVEFORM
GENERATOR
L.E.D.
(SLOPE)
D.C.
N.S. FILTER
To TL Tp
I I I
CONVERGENCE ~ I
PERIOD AND :
OUTPUT TRIGGER I
K
~
j{
--+-
-;>
NORMAL lIDAR
RETURNS
I BACKGROUND ADJ I
FIBER OPTIC
CABLES
"SLOPE" L.E.D.
OUTPUT
LINEAR DISPLAY
PLUME PULSE
"SPIKE" L.E.D.
OR GaAs LASER
II
II = Front Panel Function
LOGGED RESPONSE
TO BOTH SIGNALS
TIME
;>
Figure VI-7
BLOCK DIAGRAM:
OPTICAL TEST SIGNAL GENERATOR 29
():)
......,
-------
<.
"
~~~; ,
.,
I'
.
"
'. .f
, .
:;\'~
.~-
~ '" .
a
.?
'-
'.
- .
'~LOPE L.E.D.
~
SPIKE L.E.D.
~
I
FIBER OPTIC
LIGHT G!JIDES
PULSE FORMING
DELAY LINE
.,....
ADDITION TO
PMT HOUSING
-
~
OPTICAL V
ATTENUATORS
Figure VI-8
LIGHT SOURCES AND OPTICAL COMPONENTS 29
co
co
-------
89
a.
an actual lidar return signal (representative of atmospheric back-
scatter) from a usual atmospheric path through clear air; i.e., with-
out any obstructions or visible plumes.
b.
an actual lidar return (representative of plume backscatter) from a
smoke plume of various reflectances which is mainly
due to particulate density and plume color.
Since the LED was not able to achieve the high-magnitude light levels
representative of intense plume return signals encountered with the Omega-l
Lidar in normal operation, the solid state laser was also included as an integ-
ral part of the optical generator. It is capable of producing light levels
(incident upon the PMT detector) at least 40 dB (four orders of magnitude or
10,000 times) greater than the normal atmospheric optical signal. This strong
signal is used during the lidar's calibration process to effectively check for
the adequate recovery of the PMT detector (no afterpulsing) after the simulated
plume signal has been shut off, adequate decay times and any memory or residual
effects in the receiver or electronics (linear or logarithmic channels) also
after the simulated plume signal has been shut off. The simulated plume is
electronically movable in range from a minimum value of 76 meters (250 feet)
continuously out to a maximum range at 760 meters (2500 feet).
The optical generator simulates lidar signals (plume and atmospheric back-
scatter) corrected for 1/R2 or in the uncorrected form [Section IV]. The
uncorrected simulated signal (linear channel) for a clear-air atmospheric back-
scatter return signal is shown in Figure VI-9 and the 1/R2 corrected signal is
given in Figure VI-IO.
The optical generator simulates real optical backscatter (atmosphere and
plume) signals representing opacity values for various plumes. The opacity
values, being selectively discrete rather than continuously adjustable, are 0%
(clear-air), 10, 20, 40, 60 and 80% (nominal). The simulation is performed
for both the linear and the logarithmic channels.
-------
90
r
Q)
"U
:J
+'
Q.
E
~
lIS
c:
01
en
Lidar Range or Time-
(400 nanoseconds/em)
Figure VI-9 Lidar Atmospheric Backscatter Signal (clear-air),
Uncorrected For 1/R2 (Optical Generator)
1
Q)
"U
:J
+'
Q.
E
~
III
c:
01
en
Lidar Range or Time .
(400 nanoseconds/em)
Figure VI-10 Lidar Atmospheric Backscatter Signal (clear-air),
Corrected For 1/R2 (Optical Generator)
-------
91
SRI International designed, constructed and installed the optical
generator (serial number 1) into the Omega-l Lidar receiver. This
unit being a prototype was installed temporarily. SRI performed their
evaluation tests on the optical generator in conjuntion with the lidar.
They found several features and characteristics ~hat could be moderately
improved, which included the installation of the solid-state laser,
mentioned above. SRI subsequently manufactured optical generator
serial number 2 (including the modifications) and sent it to Denver
to be permanently installed into the lidar. Unit #1 was returned to
SRI.
With the permanent optical generator (SIN #2) installed and proper
performance verified, it was subjected to an exacting calibration at
NEIC. All signal levels, used in the opacity calculations, were measured.
to within a fraction of a percent of the actual values. The precise
value of each discrete (nominal) opacity value; i.e., 0, 10, 20, 40, 60,
and 80%, was measured. They were as follows:
Table VI-2
OPTICAL GENERATOR EVALUATION TEST RESULTSa
Nominal Opacity (%)
Calibrated (measured)
Opacity (%)
Standard Deviation (%)
o
10
20
40
60
80
0.6
10.3
19.4
40.3
62.8
79.7
0.45
0.31
0.30
0.30
0.33
0.44
a November 1979
The optical generator is
calibration in which all the
the respective opacity value
percent.
periodically subjected to this exacting
necessary signal levels are measured and
calculated to within a fraction of a
-------
92
CORRECTIVE ACTION PERFORMED ON THE OMEGA-l LIDAR
After the aerosol chamber tests and the optical generator evaluation (SIN #1)
were completed, the Omega-l Lidar was returned to Denver. NEIC personnel began
the task of correcting the problems that were encountered during the SRI tests.
Each problem will now be briefly discussed along with the corrective action
perf~rmed.
Electromagnetic Interference (EM!)
The problem of EMI from the laser's Pockel Cell Q-Switch was uncovered
during the aerosol chamber tests at SRI International [Section VI. A.]. The
problem was temporarily fixed at SRI. Once back in Denver remedial action was
taken to permanently fix the problem.
All Q-Switch power supply and remote control cable wiring was completely
rerouted away from the electronic signal cable which carries the video signals
from the photomultiplier detector to the linear and logarthmic processing elec-
tronics located in the equipment rack in the computer room. The video cable
(double-shielded) was also rerouted along a more quiescent path to the equip-
ment rack. The shields were terminated to ground at both ends. The high volt-
age cables (two coaxial cables) from the Q-switch, located in the laser's op-
tical rails, were twisted and a permanent shield added and terminated to ground
at both ends. Also the Q-Switch was returned to the supplier and reworked.
It had a KDP (potassium dihydrogen phosphate) optical crystal (electro-optical
modulator) which required 15,000 volts DC to fully energize. This crystal was
changed to a KD*P (potassium dideuterium phosphate) crystal requiring 6,500
volts DC for full operation. The new crystal provided the same operational
characteristics in the Q-Switch with a significantly less electrical transfer
energy value. This also decreased the amount of EMI present within the system.
Once all these modifications were completed the entire lidar receiver was
tested using the precision signals of the optical generator as a source. for
the PMT.
-------
93
Prior to the modification, the EMI noise occurred over an interval of 160
nanoseconds from time-value 230 nanoseconds into the receiver1s turn-on cycle,
to time-value 390 nanoseconds as shown in Figure VI-II.
o
230
390
Zero Signal Interval
Sampled by Computer
~ ~Laser fires
I 11- - - - -
600 690
710
----
Receiver
Turned on
i/
EMI Interval
(160 nsec)
t
Lidar data gathered
Nanoseconds --
Figure VI-ll
Lidar Receiver Time Cycle (each shot)
The optical generator tests (the electronics of the Q-Switch system was
operated) revealed that the EMI noise level was reduced to the level of the
inherent receiver noise which is always present in the interval from 0 nanosec
to 710 nanosec, when the laser fires. Also the optical generator signals were
turned off (atmospheric backscatter simulation signal and the plume spike signal)
and the receiver was tested at the zero-signal level throughout the entire
lidar time intervals of 4 microseconds and 10 microseconds. There was no evi-
dence of any EMI noise present. Then the entire lidar system was operated
with the laser fired into the atmosphere. No EMI noise above the inherent
zero-signal level was present in the receiver. Thus, the EMI problem was suc-
cessfully corrected.
Laser Beam Pattern
During the aerosol chamber tests, a noticeable amount of laser energy in
the first secondary maximum, that surrounded the intense central spot of the
laser beam, was detected. This resulted in a significant reflection signal
from the front surface of the aerosol chamber. At SRI the optical train of
the laser was in alignment. It was concluded that the upcollimator would have
to be refocused and realigned within the optical rails of the laser.
-------
94
The upcollimator was removed from the laser assembly and taken to the
NEIC Optics Laboratory. It was disassembled and carefully cleaned. The inside
of the upcollimator was bare, shiny metal, and it was sprayed with a flat black
paint. The upcollimator was again assembled and prepared for focus adjustments.
The assembly was focused using a 5-milliwatt He-Ne laser and aimed down a hall-
way about 500 feet in length. The focus adjustment was carried out to achieve
minimum beam divergence (beam spread over distance). The measured beam diver-
gence was slightly less than 0.2 milliradians. Once this was achieved the
focus mechanism was locked in place in order to prevent any further inadvertent
adjustment.
The upcollimator was placed in its proper position at the front of the
laser's invar rails and aligned so that the laser beam would propagate down
the assembly's principal axis which was not the case before the focusing task.
Diagnostic tests were performed by aiming and firing the lidar at a smoke gen-
erator without the smoke being present. The intense central beam was brought
very close to the lip of the stack without actually hitting the stack, and
there was no reflective return signal observed with the lidar receiver. The
corrective action was quite successful.
Lidar Receiver Detailed Performance Evaluation
With the optical generator permanently (S/N #2) installed and fully cali-
brated (Table VI-2), the entire lidar receiver was subjected to a precise per-
formance evaluation. The performance evaluation of the linear video channel
and the logarithmic video channel was conducted separately.
Linear channel
The results and conclusions for the linear channel of the lidar1s receiver/
signal processing system is now presented. As the first order of business the
performance of the photomultiplier (PMT) detector was verified again. (The
performance of the PMT was evaluated by SRI International during the aerosol
chamber tests.)
-------
95
The PMT was checked for gain linearity as a function of its (power-supply)
input high-voltage which ranges from 1.0 KVDC to 2.9 KVDC. The results of these
tests are presented in Figure VI-12. The gain linearity is quite good throughout
the high voltage range. This is especially true for high voltage values below
2.3 KVDC which is the normal operating range for the PMT in the lidar's field use.
The performance evaluation of the linear channel was conducted using the
optical generator as the input optical signal. The opacity values from 0
through 80% (nominal, see Table VI-2) were measured as a function of PMT high
voltage from 1.0 KVDC through 2.9 KVDC in 100 volt steps or increments. Each
opacity value was calculated 24 times for each opacity selection on the optical
generator and PMT high voltage setting. The opacity values of 0, 10, 20, 40,
60 and 80% were measured for each PMT high voltage setting. A total of 2,880
opacity calculations were performed. All these data were analyzed in the lidar1s
computer.
The results all summarized together; i.e., all opacity values over the
entire PMT high voltage range, revealed that the lidar1s linear channel consis-
tently measures and computes opacity to within approximately 1% of the calibra-
ted value (actual values: mean difference of 0.2% with a standard deviation
of 0.6% based on 2,880 data values).
The correlation of measured opacity values (0 to 80% nominal) to the re-
spective calibrated (optical generator) values as a function of PMT high vol-
tage settings was calculated. The results are given in Table VI-3.
Table VI-3
LINEAR CHANNEL EVALUATION TEST RESULTSa
Optical Generator
Nominal Opacity (%)
Difference from
Calibrated Value (%)
Standard
Deviation (%)
o
10
20
40
60
80
-0.1
+0.1
+0.3
+0.2
-0.6
-1.9
0.1
0.3
0.3
0.4
0.8
0.6
a
PMT High-Voltage Operating Range:
1.0 to 2.9 KVDC.
-------
'i i T.
, I
-,-
~
>
~
G>
CD
OS
...
:" - t - -' ~'."
--1 .--C.;.~
, !,:
o
>
. . .
.s:
CD
I
I-
~
[l.
j
I
i
..:.~--!-~..:.;..
~;
8.1"
7.",
f.I"
5.1'
4.1' -1
j !
j
i ,I
~ : i
, ,
, -
, :
H~I~m;
.
; ,
~'--'-
l' ,.:
" . .
-.,;
2/' ;
1 .-
1-
.
, ,
~:..;.~~ ~f
I,
----+-+ ...---
"
"
. .
j,
I...
1 "
1':. f---~
,L:
:'v'po
t
.
i
i
,: :",1
., ,
"
:! ,-
..
I.. ....
::k: ,:::::
T:
...1::
"I'
-.....
,,',:
'-
"'::':;;"
..
L
- -. ..
..
"..+
,:
':
..
'..
..
"
,"
I;; Ii; ~
H
..,
~ t ; t .."
"
". .-
..'
"
'..
..
..
.: "
, .., ::, ,,"
'..
..,
t... .
..,
..
'. . .
..,.
..
....
.-. ....
-
..
....
..,
'" t,,-.,
'H.
~
t
I' ,
- 1 1+
I
'-- .'- I-- r
, :) ""1,1..1 H' "HI,..
I t t + t.. t:H ,. ,+~ -+q. t;~1 .IH ....1.
f t +t.t ++H +..+ .H' It+ .ttt tH, H-I~ It.,
1.
.01
,
.02
.03
.04
.05 .06 .OJ.moo.1
..-. -.,.
'..
I' ,
.., ".-
t."
"t..,
..,
...
..
'..
.:!'
I .
,
+
,
-- --- -
~-
J
: 1"-~'
I
. t .
-
.
, ,
... - ..;.
...... ---- --
:
1
I
l
,
, ,,+:"'" r!., "
': .:it r'c,:'
:;! :,: ,- ,.:
;:
..,
"
h.L
",:'
I', ":
',' ..
- .. f "..:-
.....
-
.. :,;
: ,,;....- ".. :::
-t::::. "J~~ ::
! ., :~: ;::t::
'----r-"
I
.. ,.-- tt
"
.".
..,
,......
,
, :'
,:
" '. "!IL' 8ft fll:
,-- . 1
'::1 ;.t: .t. ~m j ~
'.. '; t1
, ..
;,
"
::: ::: ...
.~,. . ..
.'
....
.. t...
" ....
H>+ " ,.
+ .,ll;
1t fqi
n'
Il',: j ;i
u-
. .t'
" . 1--'--'--,
,: :
.t.-,-,
, ,
",,: :;,'
.. ,-. .,-
"., .
...
" '.
'"
I::: HH :,1::: :~H
...- .-.,.
..
.--:: ~+-
.... ~ ~I-
.-+ ..
..
i ..
"
. ...
.. ,..,-
"
..!".
'C' 1
I .:. .......-,--~+-
i, Hj" i
.1::::: "j
. .'.- ~t~~ ..Ii '-f-::' ':, .---- '~f;:-~ .~-. ,---
:: ':, :r' "::1:
.",.. .. .,.. .-,.,+
, .
,
,
- - .
. .'
-r-'" -
-+.... .....
"
,...
, ,
,
..i
1 :
..
. '
..
..'::; ':.
, I "":= ,i.l, ~ 'h 1
.. . . .t ~ ,: ~ t t J ~
"
...' .
,,,
.. ., ""f.--'
"':::::',:1:::: ,,:;':::: ".
..., ,.. ..~. t t" O"i'
.. ..
"'''I'H
,J" 'J;I"T:"]"}:":1" d;T:"l,:"1:'ld:':1'
. :, 't': ,," ;"i ....;,tH, '')' ""1'" H"
~.; ~+" rH r~H!H~'H' '11+ "H-+~:tH,t-+H
02
0.3
I I I .
0.4 0.5 0.60.7 .8 .9 1.0.
..
..,...
"
,',
..-
,H'
, . '
~ ,
" .,j,'
1 1;.>+ ~u; ; f
.
:'
j. ..
1
I
1:
~Le-
"'.
,"
, ".i"
... -.- - - -.... -.-..-....
.,.1,,-
'--
,',
-.
---,
"
:
..
..
}
"T.
~
! I
i: h.
... :;
,..
, ,
, ..
"
., ,
: ,:,
..,.
I
:j
::','
: - :::
, ,
..' :' li
;1:;
,1:,: jj
<:
'J;
- .-
" ,
.. ..
..
..'
''',
..
".
;
-~
,... ..
,..
, ,
..,
"
: I I 't..,'I""I..,
'" ". ""0'''''
..
... ......,.
..
... ". "
" ...-++-+
"
., '''' .'......
.... ,... 'H.
, .
,+ 'J T ,:-- 10-,
. ", " i'" '"'' '~.~. t+., ~t. .i, Hi! H-+! H!'
0' t,. t t tt': t-+H H "It t.+ +~tf tH+ I.t'l
-+ +:' HH'" ........ HH Iii' ttt HO' t-t...~ +H-t ;t~.
:':': ~ Normal F
.. ,.., J Operating r
'1' ,- t ';'1:"1:~: ::'+"::I'~'~:ln~':li7 i-+:;j' i':J", ,I.:
, t .~.. .'H .:'. +1.1 'I" " ,. 't" i;t' :'" 'It!
; t.. ++,. .~.. ,'" -... 'H' ~fH .... tttt t+:' tt~t
!!!H;t.
.,'
i
.
ii:
..,
: 'i
;,,;
I
. . , .
Figure VI-12 Omega-1 Lidar,
Photomultiplier Tube (PMT) Linearity
':
"
"
.. ..
..
"
,..
.
I'
" IH
..,
I'
..:
I::
..
I .
. ,
i;
,
"
:
'::i
"
.. H'
: ,t; :
:....
, , ,
;,
.. ."''''
.f. ... ..
"
",
... - ... -
';: ',:
~- -;--
'j;, ,:
- ... ... ...
"
: : :.'.' ::
.' "!.;..:-~ ,.'
~~.. ' .--::.. '"
" ..
,-."
.. ...'
-,..
"i"
...
.. to ...
..H-. '....
"""'"
~~
. ,
2A)
3.@
4.0 iio 60 108. 9. io.o 20 30 40
PMT Output Signal (Volts)
50 6n 70ia09nmo
..
~ i !,. ;:, ~'r:
"
..,
",--'"
=:=i:,
£.~,.,.
""".,..."
"
,-,
"...
.. .~
..-...
-... -...
~
'..'
.. '....
.".
.,........
.... .........-
,..
"..
---
...-
.....-
Pt. .,....."
.....,
.' :::1 ',j'
: "t~i
". ...
.. ...
..
..,~ ..+.
.,.. ,.,.
......--
'.., ::::r
.. ,..
. ... . .~.
, ,
.. ::1::
--....... -
. .. ....
, ,
...
,...
... ,.,.......
,..
....
..
.......,......
I.C
C"I
-------
97
The 80% value in Table VI-3 has the largest deviation from the optical
generator's calibrated value (-1.9%). This is due to the larger inherent error
in the linear channel at high opacity values as depicted in Figure V-7.
Logarithmic Channel
During the performance evaluation tests at SRI International, the logarith-
mic video amplifier was also subjected to tests separately. When driven with
a clean exponentially decaying signal the output signal of the logarithmic
amplifier should have been a smooth linear ramp. However, there was a notice-
able offset in this linear ramp as viewed on the lidar oscilloscope. This
offset occurred about midway in the amplitude range of the linear ramp. This
effect, termed an electronic artifact, was not investigated further at SRI.
When the lidar had been returned to Denver, diagnostic tests were carried
out on the log amplifier. The source was isolated to a capacitor not performing
properly. This problem was corrected and the tests resumed. The electronic
artifact was fully corrected. The artifact was not due to the Biomation (digi-
tizer) unit. During the diagnostic tests the digitizer was removed from the
test setup.
A linearity check was performed on the output signal of the logarithmic
amplifier (exponentially decaying signal as the input signal). The output was
linear to within 0.53 dB (decibel) of the ideal linear signal. The specifica-
tions given by the manufacturer listed the linearity as IIless than 1.0 dB.1I
The total bandwidth of this amplifier is 100 dB (10 decades) and the linearity
is about 0.5% of this bandwidth.
The performance evaluation of the logarithmic channel was also conducted
using the optical generator as the input optical signal for the lidar receiver.
The opacity values from 0 through 80% (nominal) were measured as a function of
PMT high voltage from 1.3 KVDC through 2.1 KVDC in 100 volt increments. The
same procedure was used as for the linear channel. The opacity values of 0,
10, 20, 40, 60 and 80% were measured, calculated 25 times for each PMT high
-------
98
voltage setting. A total of 2,600 opacity calculations were performed.
data were analyzed in the lidar's computer.
These
The results of the opacity data analysis yielded the following:
Table VI-4
LOGARITHMIC CHANNEL EVALUATION TEST RESULTSa
Optical Generator
Nominal Opacity (%)
Difference from
Calibrated Value (%)
Standard
Deviation (%)
o
10
20
40
60
80
-6.6
-2.2
+0.2
+0. 1
-0.3
-0.2
0.5
0.5
0.5
0.3
0.4
0.4
a PMT High-Voltage Operating Range:
1.5 to 2.1 KVDC (normal).
These data clearly indicate that the lidar's logarithmic channel consis-
tently measures and calculates opacity to within 1% of the calibrated value
for the opacity range from 20 through 80% (the mean difference range from +0.1
to -0.3% with a maximum standard deviation of 0.5%).
The logarithmic channel gives rise to a significant negative error (calcu-
lates opacity to be less than the actual values) at 10 and 0% or clear air.
As discussed in Section V of this report, this channel was designed for use in
quantitative measurement of opacity values greater than 40% and in atmospheric
conditions of heavy particulate burden or loading. The logarithmic channel is
not used for opacities below 40% in the field. The linear channel is more
accurate at low opacity values.
Field Experimentation
The Omega-l Lidar has been used in the field to monitor the opacity of
particulate emissions from numerous stationary sources. Nearly all the sources
were monitored during both day- and nighttime hours.
-------
99
The types of stationary sources monitored were the following:
. Camp George West Smoke Generator
. Cement Manufacturing Plant
. Refineries
. Glass Plant
. Steel Plant (roof monitors)
. Power Plants
The smoke generator located at Camp George West in Golden, Colorado, was
used as a stationary source of particulate emissions for the 1idar. A total
of 45 opacity monitoring runs using both black and white smoke were conducted.
Some of the runs were conducted when the plume and localized atmospheric condi-
tions were reasonably stable. (The smoke generator test site is located at
the foot of Table Mountain and wind ,conditions to 20 to 30 knots is not at all
uncommon.) The remainder of the runs were carried out under windy conditions
when the generator's plume was moving at right angles to the 1idar's 1ine-of-
sight (1.0.5) and then downwind along the 1.0.5. Under this latter condition,
the plume was fumigating the 1.0.5.
The purpose of these tests was to provide field operating experience to
the operating personnel under widely varied conditions with control over the
opacity of the smoke, and to provide a comparison between the opacity values
measured with the 1idar and those of the smoke generator's transmissometer.
The smoke generator has a white light (tungsten lamp) transmissometer
physically located about halfway up its 5 meter stack. It has an electronic
integration time of about 5 to 7 seconds. It responds slowly to changes in
plume opacity in the stack. The 1idar measures the opacity of the plume in
about 15 nanoseconds (1 nanosecond = 10-9 seconds; the transmissometer's measure-
ment time is 4 . 108 times longer than that of the 1idar) which is essentially
instantaneous.
The transmissometer was used as a monitor in order to adjust the opacity
of the black and white smoke. Because of the lengthy electronic integration
time of the transmissometer, it would lag in the indicated opacity value in
-------
100
the generator's stack. An example is, if the opacity was raised from 40 to
80% gradually, the lidar would measure the opacity at any given time more pre-
cisely and accurately than would the transmissometer due to the lag time.
The smoke generator was, for the most part, not a source of constant opa-
city plumes. Plume oP?city would fluctuate (visually observed) or become er-
ratic during the tests. The smoke generator's opacity values were limited to
the range from 0% to about 75%. Above this range the generator was quite un-
stable and the transmissometer1s output values were difficult to read with any
reasonable accuracy.
The lidar would instantaneously measure the opacity of the smoke just
above the stack. The transmissometer would tend to average out the high and
low points or opacity values, and would not closely or precisely monitor the
true opacity. Also it was observed that the plume opacity would always fluc-
tuate when the wind was blowing.
The data recorded during the 45 runs were subjected to analysis and the
results were tabulated. Each data run was .a minimum of 5 minutes (30 measure-
ments or data points).in length. The opacity values, as measured with the
lidar and the smoke generator's transmissometer, selected for several data
runs over the above-mentioned opacity range are given in Table VI-5.
The standard deviation (cr) indicates the amount of variability of the
plume opacity based solely upon a data value recorded on a repetitive 10-second
interval. (The opacity values between the successive 10-second measurements
were not recorded with either instrument.) With respect to the 10-second in-
tervals (30 data points) in a given 5-minute time period, a standard deviation
of 0.7% indicates a stable plume at those data points, while a standard devia-
tion of 7.8% shows that the plume variability was quite high.
The analyzed opacity data showed that the lidar opacity values ranged
from 0% difference to -2%, with respect to the smoke generator transmissometer,
for 80% of the reduced data runs. This is due to the fact that the optical
extinction for white light is slightly greater than that for red light. For
-------
101
93% of the reduced data runs the difference in plume opacity ranged from + 1%
to -2%. For about 7% of the reduced data runs the lidar opacity was slightly
greater than the transmissometer value by 4% or less. In these latter data
the positive error was due to ambient dust, being generated by vehicles opera-
ting nearby, present in the near region of the lidar's line-of-sight. However,
the data were retained because the standard deviation of the lidar opacity
values were less than the 8% limit set forth in the Opacity Data Acceptance/
Rejection Criterion (Sections V and VIII).
From the data used to compile Table VI-5 six of the respective data runs
were plotted with opacity as a function of the lO-second discrete time inter-
vals over a minimum 5 minute period. These graphical plots are shown in
Figures VI-13 through VI-18. Some show moderate plume opacity variability
while others indicate extensive variability. The green and red lines between
each discrete data point in each figure are included for the reader's ease of
reading the graph and do not indicate a precise variation of plume opacity
with respect to time. The effect of the transmissometer's long electronic
integration is easily observed in some of the figures. This is especially true
in Figures VI-16 through VI-18. The transmissometer was tracking the larger
changes in plume opaci'ty, however, there was a significant lag time with respect
to the lidar data. This transmissometer was not able to measure the extreme
opacity values, especially in Figure VI-18, but rather tended to average the
rapid opacity changes.
In Figure VI-18 the plume opacity values, as measured with the lidar,
ranged from 45 to 73% while those from the transmissometer ranged from 53 to
62%. Even with the high plume variability the average opacity over the 5-minute
time interval for both intruments was 55%. This indicates that there is good
agreement between the average opacity values obtained with the lidar and an
with instack transmissometer which is properly located within the source and
properly calibrated/operated.
The lidar would measure the opacity of the smoke just above the stack
instantaneously. The transmissometer would tend ta average out the-high and
-------
102
Table VI-5
LIDAR VS SMOKE GENERATOR OPACITY TEST RESULT SUMMARY
Li dar
Opacity
(%) 0(%)
Transmissometer
Opacity a
(%) 0(%)
o
5
10
10
11
15
18
20
31
31
45
55
60
60
71
1
2.5
2.7
3.4
3.2
3.5
2.5
3.2
3.4
4.3b
6.5b
7.8b
3.4
5.8b
0.7
o
4
10
11
10
16
20
20
32
32
41
55
62
60
72
o
0.4
0.4
1.1
0.4
1.7
1.7
0.6
1.5
2.9
2.1
2.2
1.4
3.0
1.4
a 0 is the calculated standard deviation for each corresponding
opacity value.
b Plume had a wide range of opacity values.
-------
~~ -
h-,-- t:Oj - S:'jOk~ aono~.., t D_.ttO~ Op 1=, 10%, cr j= ~'41%+ - t
g ~ - t- r ~ If'! 1- I '; ; '; !-
4°,T ,,' qj~' I t:t-r
,- : ~ ii, ~) j , ,--+H ,l !
30. -1 ' 1-, ; , - - I 'r- I
- ~T - ~ .., --r'" ~ -+ r
20 . -4 L --, ~-- - -J:-~ ~t~ ~~
,j ~i ! j 'i
i I I ! I.
. - - i +-~
~~H~~
I
I
I
10
I :'1 1
:- r =t:i
,- ~ t - - j ~ ~ r.. \ -1
. --r--j ~ -( -- 1 ~-
r 1 -'- i
- +~ t - I ,1 j ,
t 'I j ;! I , .
r ~ j
I - 1--- -
1
I
j
j
1
JI
,
1
r
1
1
Red - Lidar Data. Op = 10%. a = 2.74%
, 1
t ~ 1
t
_I-
I
t-t-
+---+
~ ~
o
f I
., I
, .
I
......
, I
. + ' ~ -1- ~.
j , L .
, '
- : + .
h-,.
-~-,-
... 4.
t- .
, ~. T
. +---t .
.+
. t-.
. '----,." 0.- t
. 1 . i ~ .
09:15
,
i ., - - .
+ '1
. t '
09:17
09:18
09:16
1 'I
,- .1
t~~~
1
I,
t
I l
[' L -
; I
j
I
, I
I
I
I
l --
I'
t --,- !
I
! - i
-+
~
-I -.'
J .j.
~ ;- J : ~ ,-
I+- ;.. t
-~ ..,--t
i
I
......0-+ T -
+ ~
j -_J
I
_J
I
,
I I
I
!
I
I -J
11
t I
J_I
I I
j ,
I I
J I
Figure VI-13 Lidar - Smoke Generator
I '
t ' T .
, ,
I
, .
} :
~ ; .
I Tests: 10% Average Opacity
: ~ i' r 4 .~r.T~-C1- 1']- ,Jf
-------
,....1
tf.,
~r
...
o
II
Q.
o
I
40
30
fT
~ }
d ~ -t' ~f ~ ~'l
Red - Lidar Data, CSp = 11%, (T = 3.16%
ereen
Smoke eenerator Data, Op = 10%, CT = 0.38%
1
-r--r
~~--+--I-
r
t
J t-
I
20 d - - 1- -- - - t-
I
\
t i
I ~~~.
I
10' _L
,
I
I t J
I -+ t
I
0
-;-
~ ~I-
~~
t
I
I
,
...-
--+--
--1-..,.......,
....... -
, t T
I
~j
;1
T
; I
I
't I
1 ...,
I
I
,-
I
--+-r-- I
1
I- --"-
t-
J.
1
--I- I.j. ,
; . t- +
. j
+ !
:~~j
J.
"----+---'--4--
,~~ .
'. '
.- ,---f-.i
+- -
10:27
-t
+-.
'I
t t
+ ++-t
t ~ t t, ~
10:215
10:26
j-- ~ " '
. ~ + t
. ~U
I
I I
\- - ~ j -+-+--l
'f ~l
lJ L~
-+-- I
I
~
-I
t
r' "
~
T
T
10:28
+
~- +. - --t..
. ,
-+
. 4 -+
-I- +.+
. f
--1 :
. .-
_,
I i
d
,1
.... I
I
j
.. -+
1
j~
I
i ~ 7t-+~~ ~
! ~ i~, l,
-+
-+
,.-J. -
, ;
,,'. ,I
..... '
. .
~
->-+- ~ f
+
r .
~__'
~ t :,:
r I
! . J .
! . . .
-... ~ . .
j J . !
--/-L, ,--
~ ~ , !
. .
. . t-~
-+-
, . , j
~ i - ..
.: ; :
--I ~ . ~
-"1 . -. ~
:::-1-
j . o-.!-
..j. . . .-
... . -+
, :.: 1
, !
I t-
. +
I 'J . 1 :
1 , ! I
[
I
'J
I
I
I
i-rf
~ +-
r'
Figure VI-14 Lidar - Smoke eenerator
1-
.j.
....~
t i +
: ! : 1
10:29
'+T ..
, . i t.~,;-
'I" -++-+--'
,:_1-t1.
, I .
10:30
I
; l
1
----1
, I
I I
+
{T
, ,
j .
I
.+
I I T
-+
~1
1
i
I
I
I
-- r - -
I
I-T+
t
I
t
Tests: 11% Average
10:31
~J
1
o pac ity
L~ ~T ~J~b
'ill t-~
- 1 ~
+ +-
-------
. . , , , ., '
I ,
f-
-1 T
-< --<
t--'
~ -t' . , .' , ,. .
~h - -;r+ ~r tn, " ;-1 . : :: ::::
~, ereen - Smoke eenerator Data, Op = 20%, tr = o.ee% -1 , ' ' ).c, I ' ' , ,~ ',T I
~ " : t 1 li' ~ i' t " ' + T T t' ,. T T 1 : 1- ' i + 1 ~ 1 , t- i' ~I 1 1-1 fl -<-f- j ~I t I .L1' 1 -f +1 'II, t, ~, , ~ 1
o ,I -'- + I, ,III r' ~ T T ,+l-t r -+ f 1 111 +11 f' J, t IT, 1. '! ~ T '
- -,.- .,..- -I- t "If + : + I, -J. ~ It- ,-t t-1
t iT t 1 I IT +-, ' t 1f ' 1.1 1 ' if r l ~ ,
t, + ~t -' ~Llr +1 ,I 11 l~tl t+1
Tit r I 1 1, I i 1
40 - - --,..... - -- --+- i-- +- ..... .... -- t+-+----L.., -4-.... - - - -- - ~ --
t 'tft,t+-'tie: 'f1fW+ttIF:nr 11: ;t, , t .,p' "'_,1
~ +) ~ I t ~ ~, -, i ttt 1 i r ~ + I r11 +., 1'- t 1: t Wt 1 ~ n F1, + -1- ll'1J t: J r" ,f1 t I 1,- il ! 1 '1
I tit, I~ I lttl .1 '1 f' I ' I ill J
30 - - '---- - ~ ' , --+ + ~ - - -!-~.... I _T- 1 t" - --.-.-
, '; t, I r 1 .1. i , (' 1 ~ t, 1 ' t't I:',' , 1 ill "I, .t, ' I 'i ( ,!, T ~' 1 ~ ! [I i ~ I -+ t Jt,' + i' '!t 'I l' L L' J H I II
1 i -t 1 .1 ~ F ~I -+ ,--+ I - T : j : 1-1' r -+-1' I -j + -, i- -, '-t..I r 1,....., ;J
I r tIt t T T i .' 1 " ~ I t } . I ,I t - - I 1 1 1 , + 1 I + I
r i- r I 1 : 1 1 ~ I r lit! l t' I' + t',~ I tit 1 1 I
I t' 11. 'II t L t- -I ~
20 1- 't - ~T j- -, : I ' 'f +'. '~r-1 -+ t -r ~ ' 'f : r J" - ' , I ,. -4-< t-r , t j t '.l 1 t' -j
f + 11 f I j. I I ~ I r I I " j I 1 I It' t t 1 f ,~I f I I
':." ~', tL t, 1 ,i fLIT Ii f ~'ilit ~! li,'- I !! : ,II .
tll I:r 1',T t :'1 I I j 1 l I I. J, I '[rl 1
I J I [ I T I L .
I I
1 -
.. ; I' I 11' . 1, r I I' r ~
f. I j t 1 ~ i i ~ , 1 j I I I' ,) ,t f t ~ t + 1 tlr I l' t i : t L ~ 1
- t-+~t f-+ l,_~~ ~ J, -'-r i i ,;-f -,-t-tr ,-1 r f-- I )~ti ~ it '~' l+~ 1 - -+- ~
t t + I I T 1 " , "1 , + I it ,~
I
-~ 11.1-t-1
~ l.~ ,~ ~J~
-j +
,
..
1.
-+
- t-+- -
I r 1 1
r -r ,~+l 1
.Lttl T jtrt-d11t'
I
1
-L + {++ t+l-j t
4 I tr !.. t 1.
-, - - I ~ -.--1 -.- --
I
t
- - - ..... ..a-.......
I
Figure VI-1e Lidar - Smoke Generator
,.....
1
I
Tests: 20% Average Opacity ~
-r-, , . , , --j.:1
o
1(.11
~~f;~: 1
+-
--j
~
... T ---""""""'Y-""- -----.--~
09:00
09:01
09:02
09:03
09:04
09:0!5
-------
~t
I
! . -l~~ ~l
I T I
I --r---'!"'"-~ "
I t
-+ I
--f! 1;,
I
t
"
'$.
.....,
Red - Lidar Data, Op = 31%, a = 3.37%
>-
~ --
(J
III
Q.
o
C3reen - Smoke C3enerator Data, Op = 32%, a- = 1.!50%
I
I
I t
I I t
--. ~ f- -+
1 ...... T t
I j
~ 1- 1
r
40
...,
I I
1 1
30
1-
I I
20' t 1
I
I
I
10
-14
I I
~ I
+
l+ I
~, I I
0' - 4' -~ - t-
" I 1
~.:__~L ;-
~- i
t 1- + .
tll I +
I
I
I
+
1
1
f
I -. t ~ J1 j
i --~~._~-~
08:43 08:44
I
I
r
I-
~: ). +;
, t -~.~;
08:41 08:42
08:39
08:40
,
. . ..' -~.o --<. .-0.
, ,
,
. -L.-4-.~ 4-
, ,
+ . . .
, I; f-
-+
+
1
. .
L +
l. .1.
. I
\ :r
! ~i ~T,~ 1, I + ~
I 1 I I T I . I' I
! ~t~-tt1"! I, j ,71:,~T~11~j ,-j
J ' I j t I
1 I . j ,1 h 11 r
I -'-----7 -i +-tt ~-+ -r~
1 r I I. J
I I I I '
1 I ~ +- I
I ] t
1 I i ~ -t--
-t- ........., - -- ; f.... _I ~ -....-I
~ J
I I J: i ~ 1 j
I I 1 I t fl I! j
: :1 I ,I + rif t~ !;iJ
Figure VI-16 Lidar - Smoke Generator ~
Tests: 31% Average Opacity
! I
t
I
--L ~ ~I
I
I I
t
t
I
- -- -t
..,:..
o
0"1
d
~b';i[1~jifr
-------
~ -
"
t.
.....,
>-
..
U
II ~ 1
Q. +
o
60
50
1
t-r
r ~
L p .
I t-t
40 r-
I ~
~~ 1 1 .
" I
. I
30 ---
I
20
+-
Red - Lidar Data, Op = ~e%. a = e.e1%
a reen
~- i
-t L
-L 1
r+
"=i~. +t~4
,
' I ., t
~ + t
1---'--+-, +-+ +
~ +
, t t 1
1 r-1
,
~, , l J 1
+-+~ 1
+
10:10
i t
--'-
,
'J
+
-r-r'-.
T
-t '~:h
-'
1
- T --
-+ +
+
~.
~
~. +-r -,
-'-+- .. .;.
+-~;--. - . . .
. .,.-+ +-
~ J.~
- .-.,
t 1 I
-T ~ ~j 1
--t
, -
-+ -r- ---,
-, ---I ----.i.
-+ +
- . .-""
~ I
- --~- - -. . -
, ,
. . . ..- -- .. . -
i' '
. ,;.+
-;-~+--'-+
.- -l- . .
i -. l 1-
t
1
t
., ~ ,
r+~
-- ]
. : -j -: +
-+-T--+ - ,
-~:-+
~
i
I
1
+- +
T T
f.t ~i:.~'~
t- -~--'
. +-
t
+
1 I
1
+~t+-+ -
~ 0-+
+ r' ~ ~ ~T: ;
. '~',:, - ~ ') ,if ~ "4, +
1 ; I . I t
+-- -r-
.). , 1
- I 1 t 1
Figure VI-17 Lidar - Smoke Generator
r
+
I '
T !
f I
Tests:
Opacity
415% Average
-------
, ,
T I
d ~ T T1~~T -~h~ ~
11
, ,
r
-!- ,
T '-t. ~ ;
I 1.'
1 + t
-+t-+-4
T
!fr-
,
. . .-(.
I+TrL T;
,..,
'*
'-'
R.d - Lidar Data, (5 = ~~%, ~ = 7.79%
P
. ~+-.
::=h
~ ~ . ..
+- - ---
..
areen - Smoke aenerator Data,
= ~~%, cy = 2.23%
, -, ~ .j
. -t---+ +-
~-+-t:~-
o
IS
a.
o
.. ~ t-.
1
, I
+ ,
1
70 ~ 1 +
" t +
I
,
1 ~ -+
1 j
, ,
60
. +-- +-
~o
'-1--'- - +' ,
L f I
, + ! l , 1 I . '-i[
T r~ . T
I J I I ! ' 1
I I
! ! I 1
I L 1- T 1 j
40 I ~ 1 t- ,r...-+-t !
I T t f I
I 1 j I I I I 1\
I '
~ J I
T 1 I I I 1- '" ,
r t
I ~ ! , I I 1 J j I t 1 1 .
I I 1 I
I 1 1 I T
30 I - ' ..... I I 1 ....' I ..... ~ --I -.i
T - T T - Figure VI-18 Lidar - Smoke aenerator
~
I II I I
T ~ i
t : t ~ 1.~ 1'1 I-J- Tests: ~~% Average Opacity
t- U
- -+ ---+ - -.1 .,--rL
~ j + '
I t I
r ~ ~ + +t
+ j ~.j t.l
'
10:28 10:30 10:31 10:32 10:33
-------
109
low points or opacity values, and would not closely or precisely monitor the
true opacity. It was observed that the plume opacity would always fluctuate
when the wind was blowing.
During two runs at the smoke generator, the plume was erratic and fumiga-
ting from light to heavy downwind along the lidar's line-of-sight through the
plume. At times the effective plume thickness was as large as 50 meters (stack
exit was 0.3 meters). This time of operation was quite valuable in that the
EPA-NEIC lidar operators were able to observe and study the nature and integrity
of the plume under the condition of fumigation through the lidar's line-of-sight.
The operator could easily tell when the plume was fumigating just by observing
the A-scope (amplitude vs. lidar range) data trace on the oscilloscope. The
lidar operator, stationed in the laser room and being an experienced visible
emission observer, could confirm to the lead operator in the computer room the
conditions that he observed. Confirmation was also made at the Smoke Generator
by the EPA technician who was recording the opacity data from the transmissometer.
The monitoring of the other types of sources was carried out during day-
and nighttime hours with the exception of the power plants. The cement plant
was chosen for its hydrated plume laden with sub-micron particulates. The
refineries, the glass plant, and the steel plant provided opacity sources ranging
in opacity from 0 to nearly 90%. The emissions points at the steel plant were
roof monitors.
The power plants provided the opportunity of using the Omega-l Lidar,
three visible emissions observers and instack transmissometers simultaneously.
At one power plant monitored, the plume was gray and its opacity was quite
low. The instack transmissometer located just about two-thirds of the way up
the stack indicated that the opacity was a few percent higher than did the
lidar and the visible emissions observers as shown in Figure VI-19. This figure
shows that the observers' opacity readings correlated reasonably well with the
lidar1s opacity data even though the gray plume was being observed against a
light sky.
-------
100
80
,......
~
'-'
>-
...
0
tIS
a.
0 60
Q)
E
:J
a..
40
o 20
12:30
Transm issom eter
/
~
} VEO '8
..
13:00
Time
Lidar
13:30
Figure VI-19 Opacity Measurement Comparison:
Lidar. In-Stack Transm issom eter. VEO's
......
......
a
-------
III
At another power plant, the plume was dark gray with a low opacity value.
The observed stack had an instack transmissometer located near the base of the
stack. Again, the three visible emissions observers took opacity readings
along with the lidar. The readings were taken late in the afternoon (approach-
ing sunset). The transmissometer indicated that the average plume opacity was
about 1% less than did the lidar or the visible emissions observers [Figure VI-20].
The correlation between the three monitoring techniques was good, in consid-
eration of the lighting conditions and the location of the transmissometer
within the stack.
In summary, the operational experience gained by the crew using the lidar
in the field was most valuable. The lidar is easily used in the field as an
accurate opacity measurement tool during both day- and nighttime hours.
-------
100 -
80
,-...
~
......,
>-
...
U
1'IS
a.
D 60
Q)
E
:J
a..
40
20
o
17:00
Lidar
~}
VEO's
Transm issometer
18:00
17:30
Time
Figure VI-20 Opacity Measurement Comparison:
......
......
N
Lidar, In-Stack Transm issom eter, VEO's
-------
VII.
LIDAR SAFETY IN THE ENVIRONMENT
Safety for the lidar operators and the public is the first and foremost
consideration in the operation of the Omega-l Lidar. This lidar was designed
with the maximum practicable laser safety concepts incorporated.30-34 It re-
quires two operators or crew members for normal operation. One operator, the
lead operator, is at his duty station in the computer room [Section V] monitor-
ing the performance of the entire lidar system. The second operator, the lidar
observer, is at his duty station in the laser room at all times while the lidar
is in operation. His function is primarily to aim the laser transmitter/ re-
ceiver into the smoke plume under investigation and continuously observe the
local environment which contains the laser's beam line.
Each lidar operator is provided with extensive training in the following
areas:
Laser Fundamentals [Class 1 and Class 4 lasers (power rating)]
Laser Beam Characteristics
Laser Hazard Analysis
Standards and Compliance Documents
Determination of Laser Hazards
Compliance/Control Measures
NEIC Lidar (Laser) Safety Program
This training not only covers the optical aspects of laser safety, but
also the operations in and around the high-voltage power supplies for the laser
cavity and the Q-switch.
Each prospective lidar operator is trained in either the
(laser) Safety Program or in the Laser Institute of America's
Course.32 The EPA-NEIC training program consists-of ab,out 50
EPA-NEIC Lidar
(LIA) Laser Safety
hours of clas:sroom,
-------
114
laboratory and field instruction which is specifically geared to the use of
high-power lasers in the atmosphere. The LIA course is 35 hours of classroom
instruction and laboratory demonstration.
When each prospective
Lidar Safety Program, this
being issued a certificate
lidar operator
person is then
of competence.
has satisfactorily completed the
certified as a lidar operator after
The lidar operators are trained regarding their individual responsibilities
in the operation of the lidar. These are basically the following:
a.
The lead operator (of the two operators) is responsible for the over-
all safe operation and maintenance of the Omega-l lidar under both
field and laboratory (test) conditions. When unsafe conditions exist
it is the lead operator's responsibility to ensure that the lidar is
not operated. He shall suspend, restrict, or terminate the operation
of the lidar's Class 4 laser system if it is deemed that proper oper-
ating conditions do not exist.
b.
Each lidar operator is required to exercise sound judgment and common
sense in the operation and maintenance of the lidar at all times.
The laser shall not be operated in a potentially dangerous environment
until the necessary safety precautions have been carried out. The
laser shall not be operated with the electro-mechanical (safeguard)
shutter inhibited or removed, in visible emissions source data
gathering.
c.
Any equipment changes/modification or alteration that would in any
way affect the safe operation and maintenance of the lidar shall be
recorded in the Omega-l Lidar Maintenance Log Book. All lidar opera-
tors shall be notified of such before they subsequently work within
the 1 i da r .
d.
The lidar operator shall not operate the laser during diagnostics
tests or at any other time, with the doors/panels removed from the
-------
115
main power supply without first installing the safeguards required
for his protection and the safety of the equipment.
e.
Only the lidar operators are permitted in the laser room when the
laser is either on standby or in operation.
f.
The lead operator is responsible for directly coordinating all opera-
tional plans near airports with the applicable officials of the
Federal Aviation Administration (FAA) prior to operation. He shall
also calculate and provide them: the approximate eye-safe distance
or range from the lidar) geographic location of the lidar within the
applicable urban area, direction of proposed operation) and operating
times to the FAA. Where available) the lead operator shall provide
the FAA with this laser line-of-sight information as a function of
the altitude intervals (500 ft) 1,000 ft intervals above ground level)
with respect to the appropriate navigational radials transmitted
from the nearest VOR (VHF omni range broadcasting station).
g.
Each lidar operator is not permitted to take dulling drugs/ medicines
and/or alcoholic beverages eight hours prior to or during the opera-
ting of the lidar.
Everyone at NEIC who works in the lidar is responsible for keeping the
entire lidar system) truck) etc.) hazard-free through appropriate operation
and maintenance.
The parameters listed in Item f are obtained at the lidar test site. The
atmospheric extinction (laser beam attenuation) along the lidar's line-of-sight
is measured by a lidar signal through clear air) and then the meteorological
visual range (R ) is calculated using the extinction coefficient obtained
mvr .
through this process. The extinction effect of the smoke plume under investi-
gation is also calculated. The two resultant factors are combined and the
approximate eye-safe distance (direct-beam viewing) is calculated. This para-
meter along with the other parameters are plotted on a flight (sectional) map.
-------
116
The elevation angle of the lidar's line-of-sight is measured at the laser pedes-
tal along with the direction (magnetic compass reference) of operation. The
intersection of the lidar's line-of-sight with the predominant flight levels
or altitudes is calculated with reference to the above mentioned VOR. These
data are then immediately telephoned to the appropriate supervisor at the local
FAA facility.
This procedure has been used in past lidar operations and it
quite effective. The FAA personnel with whom the lidar personnel
in past investigations, have been well pleased with the detail of
given them.
has been
have worked
information
The basic rules concerned with the safe operation of the lidar are the
following:
a.
The Omega-I Lidar shall be operated only when conditions are conducive
to safe operation for both the lidar crew and the public in the imme-
diate environs of the lidar. The laser shall not be fired if people,
aircraft, etc. are visible within, or anywhere near, the field-of-view
of the aiming telescope [Figure V-I]. The field-of-view of this
small telescope is 1,135 times greater than the beam width of the
laser pulses. The large 8-inch receiver telescope can also be used
for a greatly magnified view along the lidar1s line-of-sight.
b.
All electrical, electronic, and optical equipment within the lidar
shall be maintained in a safe operating condition. Preventive main-
tenance/inspections shall be performed on the laser including the
optical and electro-mechanical components within the invar optical
rails, the main power supply and the Pockels Cell power supply once-
weekly while in use, and as otherwise required. Proper operation of
all interlocks and other electrical-safety devices will be verified
at those times.
-------
117
c.
When the lidar is operated in the interrogation of a visible emissions
source or for any other purpose, one of the two lidar crew members
is required to be in the laser room serving as safety observer.
This person shall continually observe the area or direction into
which the laser beam is being discharged. This person shall be in
direct communications with the other lidar crew member located in
the computer room via the lidar intercommunications system. This
observer shall physically have in his hands the laser "inhibit-switch"
which, when activated, prevents the laser operation. The observer
will actuate the "inhibit-switchll if personnel, aircraft, etc., come
into or anywhere near the field-of-view of the aiming telescope. In
an area where people, aircraft, etc., (Item a) are periodically any-
where near to the field-of-view (fov) of the aiming telescope, the
laser shall be operated from the safety observer's duty station with
the remote "fire-switch" which is located adjacent to the aiming
telescope. (The fire-switch is a guarded toggle switch placed out
of the way of personnel traffic/motion so as to prevent inadvertent
firing of the laser).
When the laser is not in operation such as during "stand-bi' times, the
laser's safety shutter shall be closed. The switch that controls the optical
shutter is located on the laser's main control panel in the computer room.
The many technical aspects of the safe operation and maintenance of the
Omega-1 Lidar are too many and too detailed to give here. They are followed
carefully to assure the safety and well-being of the lidar crews and the public.
Whenever the high voltage power supplies of the laser are subject to maintenance
and diagnostic tests two lidar crew members are present to preclude any further
possibility of carelessness, such as the improper use of tools, when the system
is energized and high voltage is present.
The detailed laser safety program fully implemented at EPA-NEIC for the
lidar has been designed and put into practice based in part upon the following
references:
-------
118
a.
American National Standard for the Safe Use of Lasers ANSI
Z 136.1-176, 8~March 1976.
b.
U.S. Army Technical Manual T8 MED 279, Control of Hazards to
Health from Laser Radiation, February 1969.
c.
Laser Institute of America Laser Safety Manual, 4th Ed.
d.
U.S. Department of Health, Education and Welfare, Regulations
for the Administration and Enforcement of the Radiation Control
for Health and Safety Act of 1968, January 1976.
e.
Laser Safety Handbook, Alex Mallow, Leon Chabot, Van Nostrand
Reinhold Co., 1978.
-------
VIII.
USE OF THE OMEGA-l LIDAR IN EPA ENFORCEMENT
It was mentioned earlier in this report that EPA is proposing the lidar
mechanism as a new alternate method to Reference Method 9 [Appendix]. By defi-
nition it is usual that the alternative method gives a negative bias (lower
value and possibly less accurate) for a given test parameter or variable with
respect to the reference method. But with the lidar mechanism this is not the
case.
In Section I of this report, an excerpt from the introduction to Method 9
states that there is a significant negative bias, and negative errors can be
made when visible emissions observers view a plume under less-than-ideal back-
ground-to-plume color/luminescent contrast conditions. On a hazy or a cloudy
day with a white or gray plume the reference method displays this negative
bias/error due to the lower contrast between the light-colored plume and the
light-colored (hazy or cloudy) background.
In this case the reference method cannot be effectively used to verify
the data obtained with the alternate method. The same holds true with using
the lidar-to-plume opacity at night which can be done very effectively. The
reference method cannot be used at night to verify the alternate method1s data.
The correlation of opacity values between the lidar and visible emissions
observers on a clear day (high background-to-plume contrast conditions) and a
hazy/cloudy day is not viable due to the inherent negative bias/error of Method 9.
As was given in Section VI of this report the lidar was thoroughly cali-
brated with the optical generator (internal calibration mechanism). Then the
lidar was subjected to tests with a smoke generator that is used to certify
visible emisssions observers in accordance with Method 9 requirements. The
-------
120
analyzed opacity data showed that the lidar opacity values ranged from 0% dif-
ference to -2%, with respect to the smoke generator transmissometer, for 80%
of the reduced data runs. For 93% of the reduced data runs the difference in
plume opacity ranged from + 1% to -2%. For about 7% of the reduced data runs
the lidar opacity was slightly greater than the transmissometer value by 4% or
less. In these latter data the positive error was due to ambient dust, being
generated by vehicles operating nearby, present in the near region of the lidar's
line-of-sight. However, the data were retained because the standard deviation
of the lidar opacity values were less than the 8% limit [Section V of this
report] set forth in the proposed regulation. (The standard deviation of an
opacity value obtained with the lidar is an indication of the atmospheric sig-
nal noise along the system1s line-of-sight within the near- and far-region pick
intervals [Section V]).
These tests have clearly demonstrated that the lidar is an acceptable
alternate method. The required correlation was not carried out with visible
emissions observations, due to the inherent negative bias, but with the smoke
generator's white-light transmissometer which is routinely used to certify the
visible emissions observers under the reference method.
It is suggested that an industrial facility, etc., would have to use a .
white-light transmissometer, properly positioned, calibrated, and operated, to
verify the opacity values concurrently recorded with the lidar. This is espe-
cially suggested during nighttime operations. (Some new source performance
standards now require in-stack transmissometers to measure opacity).
The EPA/NEIC Omega-1 Lidar will be used extensively to make opacity mea-
surements on visible emissions from stationary sources for enforcement purposes.
Measurements will be made of the optical opacity of particulate emissions from
large and small diameter stacks alike [Section V]. It is an effective remote
sensing tool for accurately measuring plume opacity during both day- and night-
lighting conditions with significantly greater accuracy over the reference
method. The lidar is not affected by background conditions such as clear sky,
cloudy sky, hills in the background, and the angle of the sun with respect to
-------
121
the lidar (the lidar receiver although solar blind cannot look directly into
the sun). The lidar does not consider plume/ background contrast in the mea-
surement of opacity.
The lidar's oscilloscope display provides a near real-time means of deter-
mining the quality and integrity of the near- and far-region atmospheric back-
scatter signals used in calculating plume opacity. At a maximum laser firing
rate of 1 pulse every 2 seconds, smoke plume opacity can be monitored for min-
utes or even hours to document the temporal variations for a particular stack
under investigation. Average plume opacity for a given time period can be
calculated along with statistical variances. A running average can also be
calculated [see Section V] giving the maximum average opacity for a given time
interval. This is a most valuable asset of the lidar in enforcement data col-
lection.
The lidar will be used to measure the opacity of hydrated or so-called
steam plumes. (To the extent practicable the lidar operators will have tech-
nical information with them regarding the respective process and the control
equipment for each stationary source to be listed. This information is usually
supplied by the respective EPA or state offices requesting the studies.) As
listed in the reference method there are two types, i.e., attached and detached
steam plumes.
Attached Steam Plumes: When condensed water vapor is present within a
plume-under-test as it emerges from the emission outlet, the opacity measure-
ments shall be made with the lidar at a point within the residual plume where
the condensed water vapor is no longer visible.
During daylight hours the lidar operator can usually locate the most dense
portion of the residual plume visually. The operator can then aim the lidar
transmitter/receiver into that portion or region of the plume. During either
day- or nighttime operations the lidar is used to locate the most-dense region
of the residual plume, i.e., the region of highest opacity. (A high intensity
spotlight is available within the Omega-1 Lidar to aid the lidar operator in
-------
122
aiming the transmitter/receiver at night). The lidar operator scans the trans-
mitter/receiver (lidar measuring opacity) along the longitudinal axis or center
line of the plume from the emissions outlet to a point just beyond the steam
plume. The steam plume will have nearly 100% opacity while the residual plume
opacity is most probably lower. If the residual plume also has a 95 to 100%
opacity then the lidar operator may also have to observe color differences as
an added assurance that the lidar is aimed completely within the residual plume.
Plume reflectivity can also be used to accomplish this same task. The steam
plume is white and highly reflective while the residual plume will be lower in
reflectivity.
Once the residual region of the plume is located (along its center line)
the lidar transmitter/receiver is then scanned perpendicular, as practicable,
to this axis in order to locate the region of highest opacity. Plume opacity
is then measured at the location within the plume. Adjustments are made to
this location of the lidar line-of-sight within the residual plume as deemed
necessary by the lidar operators to correct for changes in wind direction,
etc.
Th~ distance from the stack to the position within the plume where these
opacity measurements are collected is readily obtained by a calculation using
the lidar range to the stack, the lidar range to the plume measurement position,
and the azimuth/elevation angles between the stack and the plume monitoring
position. The geometry for the calculation along with the 3- and 2- dimensional
equations are given in Figure VIII-l. Ro~ is the range from the emission point
to the plume measurement position. R, R , ~ , ~ , and ~ are measured with
s p s p
the lidar. Ro~ is calculated and recorded for each position of the lidar line-
of-sight while the tests are being conducted.
Detached Steam Plumes: When the water vapor in a hydrated plume condenses
and becomes visible at a finite distance from the stack or source emissions
outlet, the opacity of the emissions is measured in a region of the smoke plume
just above the emissions outlet prior to the condensation of the water vapor.
The condensation of the water vapor in the source emissions forms the steam
plume which appears white, and is usually about 100% opacity.
-------
Z
123
P (R , 1/1,13 ), P (x, y, z)
p p p p
I
I
I
,Stack outle~
,
I
I
(plume measurement position)
PS(RS' 0, Bs)' Ps(o, y, z)
y
x
--- '\. I /
----- "1/
Projection of Ro~ "~
onto the xy-plane ~ Projection
of Ponto
. p
the xy-plane
Distance from Ps to Pp = R01/l
h
R01/l = IPp - Psi = [(xp - xS)2 + (Yp - Ys)2 + (zp - ZS)2J2, in rectangular coordinates.
Perform a transformation to spherical coordinates:
x = RSinBCos1/l, y = RSinBSin1/l, Z = RCosB
R01/l = [(RpSi n(¥ -
- R Sin(¥ -
s
13 )C05(~ - 1/1) - 0)2 + (R Sin(¥ -
p p
S5)Sin(~ - 1/1))2 + (RpC05(¥ - Bp)
Bp)Sin(¥ - 1/1)
II h
- R C05(2 - 13 ))2J2
S S'
Sin(¥ - 1/1) = 1 for 1/1 = 0, and Sin(¥ - S)=C05S, Cos(~ - s)=Sins, C~5(¥ - 1/I)=Sin1/l
1
R01/l=[(RpCosBpSin1/l)2 + (RpCOSBpCOS1/l - RsCOSBs)2 + (RpSinBp - RsSinSs)2J~
Finally, the equation for R01/l becomes:
1
R01/l = [Rp2 + RS2 - 2RpRs(COSBpCOSBsCOS1/l + SinSpSinBs)J~
If 1/1 = 0, i.e., the lidar beam is aimed directly over the stack outlet,
R01/l + Roo and
Roo = [R 2 + R 2 - 2R R Cos(s - S )J\, (2 dimensions).
p s p s p s
Figure VIII-lo
Range Calculation for Plume Measurement Position
-------
124
During daylight hours the lidar operator can visually determine if the
steam plume is detached from the source outlet. At night a high intensity
spotlight within the Omega-1 Lidar, aids in determining if the steam plume is
detached. The lidar is also used to determine if the steam plume is detached
from the emissions outlet by repeatedly measuring plume opacity, from the outlet
to the steam plume along its longitudinal axis or center line, and/or observing
plume reflectance. Once the determination of a detached steam plume has been
confirmed, the lidar is then aimed into the region of the plume between the
outlet and the formation of the steam plume, usually about one half a stack
diameter above the outlet. The lidar transmitter/ receiver is then scanned
across the plume to locate the region of greatest plume opacity. Plume opacity
is subsequently measured at this location. Adjustments are made to the location
of the lidar1s line-of-sight within the plume as deemed necessary by one of
the lidar operators to correct for changes in wind direction, air temperature
changes, etc. The location of the lidar's line-of-sight within the plume is
recorded for each position while the tests are being conducted.
Opacity Data Reduction Mechanism: As proposed in Alternate Method 1, the
temporal length of an individual data run may extend from 1 or 2 minutes, such
as for intermittent sources, to over an hour or even longer depending usually
upon the characteristics and variability of the source emissions. The lidar
data rate is nominally set at one opacity measurement every 10 seconds through-
out a given data run.
The manner in which the opacity data values from a given data run are
reduced after the lidar data has been processed by computer, is a function of
the air quality regulation to be enforced. When a given State Air Pollution
(SAP) Control Regulation specifies a maximum permitted opacity value over a
fixed time period (Example: Plume opacity shall not exceed 50% for a continuous
period of no more than 5 minutes in any 60 consecutive minutes), then that
time period or interval shall be used in the reduction of the opacity data.
If the respective regulation specifies and opacity limit for an I-minute interval
and the data run were I minutes in length, then all the opacity values, measured
on the 10-second repetitive cycle and processed for this interval, are averaged
-------
125
yielding an average opacity for this interval. If the average opacity is greater
than that permitted by the regulation then the source is in violation.
The average plume opacity. 0 . for the
p
as the average of the consecutive (in time)
values. 0 . by using Equation VIII-lo (The
p
the "averaging interval").
I-minute time interval is
individual lidar-measured
I-minute time interval is
calculated
opacity
ca 11 ed
1
o =1 1: 0
p 1 k=l pk
(VIII-I)
where:
o k = the kth opacity value in the (I-minute) averaging
p interval.
~
= the sum of the individual opacity values.
= number of individual opacity values contained in the
averaging interval.
o = average opacity over the averaging interval.
p
If the respective regulation specifies an opacity limit for an I-minute
interval and the data run were J-minutes in length (J > I). then a running
average or progressive average is used to reduce the lidar opacity values for
a given data run. The mechanism for the running average is shown in Figure
VIII-2. The I-minute interval is maintained constant in length (temporal)
being moved along the entire length of the J-minute data run. If i opacity
values. from 1 to i. have been averaged for the I-minute time interval by Eq
(VIII-I), the running average is performed by successively subtracting the mth
value and adding the m + 1 value and calculating the average for those i opacity
values again. then subtract the m + 1 value and add the n + 2 value and perform
the calculation again. etc.
The running average is a computational tool which locates the I-minute
interval within J that has the highest average opacity. This applies directly
to the example given above. i.e., the 5-minute period (1=5) in any 60 consecu-
tive minute period (J=60). The number of values averaged in this manner will
not always be equal to a constant i. but the time interval I will be the same
-------
126
I""
J
..\
~I*
1-1-1-1
1 2 3 4
1
I
I
j
(a)
First average opacity, 0p' calculated for the i opacity values
I~
I I I
I-~
I I
1 2 3 4 . . . i i+l
j
(b)
Second average opacity calculated, first opacity value subtracted and the
(i+l) value added.
~
I I I
1 2 3 4
1 ---'--i
I I I
. . . i i + 1 i+2
j
(c)
Third average opacity calculated, second opacity value subtracted and the
(i+2) value added.
I I I
1 2 3 4 . . . i i+l i+2
. . . . .
I-
I I
m-l m m+l
I~
I I
n-l n n+l n+2
j
(d)
The mth average opacity calculated.
I I I
1 2 3 4 . . . i i+l i+2
~I
I I
j-i ...j-2 j-l j
.1
j
(e)
The last average opacity calculated over the time interval I.
*1 is the averaging interval established by State/Local Regulation.
Figure VIII-2.
Pictoral Diagram of the Running Average.
-------
127
throughout J. A few of the i values may possibly be rejected due to the Opacity
Data Acceptance/Rejection Criterion presented later in this section.
When applicable control regulation specifies a maximum opacity value as a
function of time, then the lidar opacity values, measured on the nominal 10-sec-
ond data rate, are reduced accordingly by computer. The time intervals over
which the opacity values exceed the maximum, given in this regulation, are
summed together within the specified consecutive or overall time period. If
the summed time period exceeds the allowable time period the source is in vio-
lation. An example of this is the following: Suppose the state regulation
states that short-term occurrences shall exceed 50% opacity from a" period aggre-
gating no more than 5 minutes in any 60 consecutive minutes and/or no more
than 20 minutes in any 24-hour period. The time intervals over which the plume
opacity exceeded 50%, are summed together. If the sum of the intervals exceeds
5 minutes in any 60 consecutive minutes then the source is in violation. The
same holds true if the source of the invididual time intervals exceeds 20-minutes
in any 24-hour period.
If there is no applicable state air pollution control regulation for the
lidar data to be reduced, then the 6-minute time interval of Reference Method
9 shall be used. The running average technique described above, shall be used
to calculate the 6-minute interval which has the highest average opacity within
a given data run. Referring to Figure VIII-2, I is equal to 6 minutes and J
is 6 minutes or longer.
The opacity of intermittent visible emissions 35 and cyclic processes is
measured over a period of time considered adequate to determine compliance/non-
compliance with the applicable regulation. A cyclic process is defined in
Figure VIII-3.
o = 0%
p
--I
t1
1-1--1
t2
I-I
Figure VIII-3 Cyclic Process
-------
128
If the regulation, such as a state
Implementation Plan (SIP), specified an
the lidar-measured opacity values shall
the requirements of the regulation.
or city regulation in an approved State
opacity limit as a function of time,
be added together in accordance with
If there is no applicable state or local regulation then the 6-minute
interval will be used as described above. If the time period of a given cycle
is less than 6 minutes, then the opacity values for this period are added to
sufficient number of zeros to obtain the 6-minute period. The average opacity
is computed from the opacity values and the added zeros. For example, if a
particular cycle was 4 minutes in length there would be 24 opacity values (4
minutes x 6 opacity values/minute). Then 12 zeros would have to be added to
bring the total to the 36 required values (6 minutes x 6 opacity values/ minute).
In the measurement of plume opacity from a sulfuric acid manufacturing
facility, the lidar line-of-sight should be positioned within the most-dense
part of the plume which will not necessarily be at the emissions outlet. The
characteristic sulfurous gas absorbs plume moisture forming sulfuric acid aero-
sols in the submicron size range.36 High values for the opacity can occur.
Often the aerosol plume does not become visible for a few stack diameters away
from the emissions outlet. This does not constitute a detached steam plume
and should not be treated as such.
Due support of 40 CFR Part 51 with opacity limits as a function of time,
Alternate Method 1 will be employed by summing the respective opacity measure-
ment time intervals for the required period of time.
Opacity Data Acceptance/Rejection Criterion: As shown in Section V, the
lidar computer calculates plume opacity by Equation (V-4) and the standard
deviation, S , of each respective opacity by Equation (V-8). S is an indicator
o 0
of the integrity of the optical backscatter signals from the near-region and
far-region of the lidar line-of-sight, and may be termed an atmospheric noise
indicator.
-------
129
In the course of reducing large amounts of lidar-measured opacity data,
it was empirically or fundamentally determined that if S is greater than 8%
o
(calculated with the plume opacity, 0 , for the selected near-region and far-
p
region pick intervals), then the lidar backscatter signal is not reliable (too
noisy) for an accurate opacity measurement. In this case the respective opacity
value is discarded.
For a given data run, if the average of the respective individual standard
deviation values (So) of a set of opacity values in an averaging interval I is
greater than 8% (also based on 100% opacity full scale) then 6 for that interval
p
is rejected and discarded from whole data run. This average is calculated
using Equation (VIII-2).
- 1 1
S = - L S
o 1 k=l ok
(VIII-2)
where:
SOk = the kth standard deviation value of the data set I,
L
= the sum of the individual standard deviations,
1
= the number of individual standard deviation values in a
given data set,
S
o
= the average standard deviation for a given data set.
Temporal Criterion for Reference Measurements:
lates plume opacity by Equation (V-4)
The lidar computer calcu-
o = 100%
P
[ 1 - ( ~;
R
n
I
n
fJ
(V-4)
This equation takes the reference
the computer calculates plume opacity.
signal pick intervals (In' If) and the
eated in Section V.
(clear air) measurement into account as
The mechanism for calculating the data
reference intervals (Rn' Rf) was del in-
There must be a criterion which describes how often and under what condi-
tions additional reference (clear air) measurements are to be made. The.tempor-
al criterion has been developed empirically from field experience with the
Omega-l Li dar.
-------
130
A reference measurement is obtained with the lidar and recorded on magnetic
tape usually within a GO-second time period prior to any given plume opacity
data run. Another reference measurement is obtained within 60 seconds after
the completion of the same data run. This is standard operating procedure
irrespective of the variability of the local atmospheric conditions along the
lidar's line-of-sight.
The reference measurement is obtained by directing the lidar's line-of-
sight near the emission1s outlet in height or elevation, and rotated horizon-
tally in an upwind direction to a position clear or free of the source struc-
ture and the associated plume. If wind conditions are calm, then the lidar
line-of-sight may be moved to either side of the plume that is free of obstruc-
tions.
The need for an additional reference measurement(s) is a function of local
atmospheric .kinetics which is usually determined through the judgment of the
lidar operators as they observe localized meteorological conditions and the
characteristics of the lidar backscatter return signals.
An additional reference measurement is usually obtained, which occurs
during a data run, if the lidar operator (safety observer in the laser room)
observes a change in wind direction or plume drift of 30° or more from the
direction that was prevalent when the last reference measurement was made.
If the lidar operator, stationed in the computer room, observes a noticeable
change in the amplitude variations in either the near-region or far-region
backscatter signal segments (not due to a common change in plume opacity) that
remains present for two plume data records (about 20 seconds), then the data
run shall be interrupted and another reference measurement shall be recorded.
(The location on tape, time, and the proper identity of each reference measure-
ment is recorded on magnetic tape). Then the data run is immediately resumed
and continued through completion. This process of obtaining additional refer-
ence measurements may be iterated as many times as required. If the ambient
(clear air) conditions along the lidar1s line-of-sight are continually changing
significantly, then reference measurements and plume data measurements are
usually recorded alternately.
-------
131
During the subsequent analysis of the lidar data, the reference and data
measurement signals are analyzed in the same sequence or order that they were
recorded in the field.
Lidar Field Calibration: As it is with any quantitative measurement in-
strument, overall system calibration is important for the lidar. A viable
means of checking and monitoring system calibration is a necessity in the en-
forcement application. Extensive calibration is carried out to support the
field data gathered for use as evidentiary material.
The Omega-l Lidar has an optical generator (built-in calibration mechanism
discussed in Section VI in detail) that tests the entire receiver, electronics
and data processing systems. This is accomplished by using a highly-controlled
small solid-state laser and light-emitting diodes (l.e.d.) to inject an optical
signal, which simulates an actual lidar return signal from a given atmospheric
path through a plume, or in clear air, into the receiver ahead of the PMT detec-
tor. The optical generator simulates real optical signals representing clear
air or 0% opacity, 10, 20, 40, 60 and 80% opacities (nominal).
Thi.s calibration test is carried out periodically in the field while the
lidar is in use, requiring about 3 to 4 minutes to perform. Each of the above
mentioned optical signals is fed into the lidar receiver and the resultant
opacity is calculated in just the same manner as the real data collected in
the field, and each value is recorded on magnetic tape (actual lidar-simulated
waveform), paper printout and in the operations log book (discussed later in
this section).
This calibration test is conducted for each new emissions source under-test
prior to any opacity measurements. The test is also performed at least once
every 4 hours during an extended run (or a series of shorter data runs) for a
given source under-test. In the Omega-1 Lidar, the field practice is usually
to perform the calibration test once-every 2 hours (elapsed time). The results
are recorded in the operations log book.
-------
132
If the lidar-measured opacity value is not within! 3% (based on full-scale
100% opacity) of the actual value of the optical generator input of each of
the two video channels:
Linear Channel
- + 3% over the opacity range of 0% through
60% (optical generator values),
Logarithmic Channel - + 3% over the opacity range of 20% through
80% (optical generator values),
then the lidar is considered out of calibration and remedial action is taken.
The optical generator itself is periodically (once-per-month) subjected
to an exacting calibration in which all signal levels are measured to within a
fraction of a percent of the required values.
The results of the performance evaluation and the calibration tests are
discussed at length in Section VI.
Elevation/Azimuth Angle Correction Criterion: To ensure true plume opacity
for enforcement data collection, the effect of the elevation angle (angle of
inclination of the 1idar transmitter/receiver) of the lidar firing through a
vertical plume is taken into consideration in the opacity calculation carried
out by the computer. The elevation angle is measured with respect to the longi-
tudinal (vertical) axis of the stack. As shown in Figure VIII-4 the optical
plume opacity is typically measured with the lidar along the inclined path L.
The opacity value ultimately required is along path P, the horizontal thickness
of the plume. The ratio of P to Lis:
P -
- - Cos ~
L P
(VIII-3)
The absolute magnitudes of P and L are not required. The angle ~p can be
obtained from the lidar pedestal for this correction. The opacity value for
the lidar path L, ° , is then mathematically modified by the angle term to
p
obtain the opacity value for the actual plume (horizontal) path or thickness,
o
pc,
0pc = 0p Cos ~p
(VIII-4)
-------
Horizontal Plane
Stack's Vertical Axis
Vertical Smoke Plume
8 , Lidar Elevation or
P Inclination Angle
P
L = Effective Plume Thickness
P = Actual Plume Thickness
P = LCOS8p
0p = Opacity measured along path L
_SL-
Lidar Line-of-Sight
Referenced to Level Ground
(Horizontal Plane)
o = Opacity value corrected to the
pc actual plume thickness, P
Smoke Stack
Fi gure VII I -4.
Elevation Angle Compensation for Vertical Plumes.
.......
w
w
-------
134
It was elected to make this correction if the effect of the elevation
angle would approach an error of 1% in plume opacity. Equation (VIII-4) becomes:
Op - 0pc = Op (1 - Cos ~p)
Solving for ~ , this gives the following:
p
f3 = Cos-1
P
[ 1 - (OPo: Ope) ] .
(VIII-5)
Using the 1% error (difference), then 0p - 0 = 0.01, and
pc
~p = Cos-1 [ 1 - °o~l ] (VIII-G)
Equation (VIII-G) is plotted in Figure VIII-5. The angle at which the
correction must be carried out to maintain the 1% error is a function of plume
opacity. The larger the opacity 0p' the smaller the elevation angle becomes
in order to stay at or below the 1% value. In Figure VIII-5 no correction is
required for the ~ values below the curve, as a function of opacity. Above
p
the curve correction is required. In terms of an inequality, if the elevation
or inclination angle ~ , is greater than or equal to the value calculated in
p
Equation VIII-G,
f3 > COS-l[l- 0.01]
p - 0
p
(VII I-7)
then the correction is performed using Equation VIII-4. So far in practice in
the field, the lidar pedestral elevation angle values have usually ranged from
+3° to +12°.
When measuring the opacity in the residual region of an attached steam
plume, the lidar shall be positioned in relation to the stack so that the lidar
line-of-sight is nearly perpendicular to the direction of the horzonital drift
of the plume, to the extent practicable. This procedure will essentially key
the lidar line-of-sight distance through the plume equal to the actual plume
thickness at the point of opacity measurement. However, if the direction of
drift of the plume should change so that the lidar line-of-sight does not pass
through the plume nearly perpendicular, then an azimuthal angle correction
-------
IT
t ~ .1. I ! . t ! - l ' L ~ I L .--:1 L r~-r----i
- t f - : f - + +
+ - - J I , j - : - ~ t t - t
- + + - - - - - + + - . t + ! + + . .; - j
I
+ . 1 - - . . - - + + - t - T - - ' , i
!= I
L + Las e r B eam In cl in at ion A ng Ie - + + - - - ~ t - - 1 + + - . ! --1
- - - - -
j + ,.. t + - + + + + - - + - 1 +
- t ! j I - - - + + -
+ + + + + + - .~j
+ -:-:-t + + t + + + + + - II
+ . . .. + + + + + + + + F igu re VIII-5 Las er Beam Incl in at io n
- + + + + + - - +
+ + + , + + + - + + +
...-- ~ A ng Ie C 0 r r e ct ion Requ irem ent -
+ + .+ + + - + + , + t ' t + +
+ + + + + + - -
+ + .. + + + + + + - . + + + (P ath D istan ce Th rou gh P lum e)
+ + + + + + + + - + + + + +
°
- + , + + + + + + + +
, + + + + + + + +
+ + + + + , + + + + + + + + + -
+ + + - + + + + - + + + +
+ - + , + + + + - + + + + + - + - + - +
+ ; \ + + .. + + + , + + + t + + + .+ + + , +.
+ : + + + - ; + +
+ + + ; + + + + ; + + + +
t t + + + + + - , +
.. + + + + + + , + + + +, t ,
+ + + + +
\' + + + + + + , + + +. + + + + + t
\ ' + + +
+ +
, + + + + +
+ ~\
- +
;
+ "
~ ------+- ~ -~_.---------
. .
+ + , C orrection Req u ired In Th is R eg ion +
- +
+ , + + , K'
+ + t ,~ ..... , + , + + + I
+ - ~ +
, t + ---:.
+ + t + + . . .! , " f___~
:---:-- ~- - ~
; t + + + + t + ~
+ , + - + + + + ~ + + t + +- ---
+ t + t + t 1 + t . + - + -
+ , + + +. + + +
+ - + + '+
+ '+ : 1
. + + . No C orrectio n Req u ired In Th is Reg ion + + - + + +
+ + t + + + + - - + +
- + H : j : t : t : t : j + + + + + . + + t
+ t . t t + + t ' , + + + + + + + + + + + + P lu e Op ac ity (0/0)
+ + m 1
+ + + + + + + - + + +
, + + t + + + + + + + + - - -1 - .' J I
I+'
OJ
(J1
60°
50
40°
30°
20°
10°
0°
o
10
20
30
40
50
60
70
80
90
100
-------
136
shall be made to the calculated opacity valves obtained under this condition.
The geometry of this correction is defined in Figure VIII-6. This correction
also applies to the other plume types if the opacity measurement is made more
than 3 source diameters away from the source outlet. The drift angle, ~, is
obtained from the following expression.
~ = Cos-1 [R12 + Rc/ - R22]
2Rl Ra
(VIII-8)
where:
Rl = the lidar range to the position within the residual plume
where opacity measurements are being performed, position 1
in Figure VIII-6(a), .
a = azimuthal angle through which the lidar transmitter/receiver
is turned in order to measure the drift angle; a > 5° as
measured on the lidar transmitter/receiver mount,-
R2 = the lidar range to the position within the plume selected in
order to measure the drift angle, Position 2 in Figure VIII-6(a),
R = the distance along the center line of the plume in the direction
a of drift, from Position 1 to Position 2 [Figure VIII-6(a)].
Rl and R2 are measured directly from
signals at the center of the plume spike.
pedestal of the lidar transmitter/receiver.
the respective plume backscatter
The angle a is ~easured at the
If e > 100° or e < 80° for 0 in the range from 50% to 100%, if ~ > 1050
- - P -
or e < 75° for 0 in the range from 20% to 40%, and if ~ > 120° or ~ < 60°
p - -
for 0 in the range from 1% to 20%, then the azimuthal correction shall be
p
performed on the lidar measured plume opacity value 0 using Equation VIII-g.
p
Ope = 0p Cas ( ~ - e) = 0p Sin e
(VIII-g)
where:
o = the opacity value measured along the lidar path L' which
p is the thickness of the plume along the lidar line-of-sight
through the plume, Position 1 in Figure VIII-6(b).
o = the actual plume opacity along the corrected path pi
pc [Figure VIII-6(b)].
A given 0 shall be used in place of its respective 0 in the Opacity
pc p
Data Reduction Mechanism given earlier in this section.
-------
137
Position of the Lidar line-of-sight
within residual plume for opacity
measurement [Position lJ.
- - - -/~
/
I
/
I
I
~
r-
R(t
c::
o
+->
V1
o
c...
o
+->
cv
g
'"
R 2 .;:::
0'"
Q:
-8
"
~
(;
~
o
I
-------
138
There may be testing situations where both the azimuth and the elevation
correction shall be performed. In this case the elevation angle correction is
made first and then the azimuth angle correction is carried out on the opacity
value already corrected for elevation.
Lidar Data Analysis Record: While the lidar data analysis and reduction
is being conducted, permanent records shall be initiated and maintained. In
these records, the paper output from a computer printer, the measured or cal-
culated values for In' SIn; If' SIf; Rn' SRn; Rf' SRf; Rs' ~s' Rp' ~p; ~, Ro~;
RI' R2' a; £; 0 , S ,0 ,along with the respective units (meters, nanoseconds,
p 0 pc
etc) are recorded for each final opacity calculation. The data processing
operations that were used to calculate the final opacity value from a given
plume data signal are easily determined from these records. During the data
reduction process the values of 6 (which were calculated from the applicable
- p
o and 0 values) and S are documented along with the applicable parameters
p pc 0
used in performing the running average. The date and time that each lidar
data signal was obtained, its respective assigned control number, its magnetic
tape file address and the tape file address of the respective reference measure-
ment are also recorded for each final opacity calculation.
The identity of each criterion used in the data analysis and the identity
of any opacity values rejected are recorded for each applicable opacity value.
Lidar Log Book: A special
tionll has been designed to be a
evidentiary purposes. The cover
custody number, the dates it was
sequence.
purpose logbook entitled IlLidar Log of Opera-
permanent record of the lidar activities for
[Figure VIII-7] of each logbook contains the
used, and the number of the next logbook in
A control number is assigned for each stationary source monitered with
the lidar. This number is assigned on the Lidar Log Control Number Tabulation
[Figure VIII-8], and is also recorded for each individual lidar backscatter
signal in the identification block on magnetic tape. This number is used for
evidentiary purposes.
-------
139
lLlDAR LOG Of OIPlElRATRONS
Log Book Number
from /
/
-------
140
UUt\K 1.0(; C:ONTItOI. NtMH.:1t TAHl'I,ATIOl\
I.o~ Hook i\ulllh.',,-
[Assian a CONTROL NUMBER to each individual source under test]
CONTROL DATE
NUMBER ASSIGNED PROJECT CITY, STATE
continuod on next paa-
Figure VIII-8 Lidar Log Control Number Tabulation
-------
141
The required data for each source under investigation is specified and
recorded on the "Lidar Log of Operations" [Figure VIII-9 and 10]. This includes
source description/characteristicst local meteorological conditions measured
at the 1idar's position and the data record log. The calibration record is in
Figure VIII-9 which gives the calibrated opacity of the optical generatort the
opacity value calculated by the 1idar computer using the optical generator as
the source and the file address on magnetic tape where the data were recorded.
The forms shown in Figures VIII-7 through 10 are bound in a sewn logbook
and are subject to EPA-NEIC document control and Chain-of-Custody regu1ations/
procedures.
As required by the Chain-of-Custody procedures for evidentiary materia1t
the magnetic tapes (Hewlett Packard cassettes containing computer programs and
the 8.5 inch g-track data tapes) are stored and carried in specialized magnetic
shielded boxes to prevent accidental erasure and the pickup of any spurious
noise. When the data tapes are returned to EPA-NEIC for data processingt they
are stored in standard shielded tape racks in the computer laboratory.
-------
142
UOAR 1.0(; Of' OPf:RATIONS
run I rul n u rnb,'r: 41 M H; ,\.
fuility .... ..4 10utlOl:
AI I~. '1.111 lit. 01
Loc'IIOI 0' UDAl:
/
/
fro..
- 10
(local II...)
Direction to source
Laser inclination 1+ angle is up;
Souee Iyp. 0111 off Idol d1l181OIlon:
Range to source
horizontal is 0°)
km
PI,," c~aracllflltlu lcolor, Ihap., Ilum pr..ul. .tc.l:
km/hr end ----":""'km/hr
°C end °C
end
end
% end
km end
Wind dlflctlon: begin
IItIOllu hmldlty: begin
Visibility: begin
end
WI,II Ip..d: begin
Air ""plfolll': begin
Barollll"r: begin
CIOIII cour: begin
%
km
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
Dolo flcordl iliad. " fI.ld IIOPII. prlntOlIl, pholo'i. 'Ie.):
MAGNETIC TAPES
tape# track# files
.-.-.-.-.-.-.
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
OPERATOR'S SIGNATURE:
DATE:
WITNESS SIGNATURE:
DATE:
Figure VIII-9 Lidar I;;og Of Operations-Sheet 1
-------
143
lIDAR OPERATOR'S NOTES
(Include position 01 IlSer bum within plume-- attached plume, etc.]
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
UDAl fUNCTION YERlflCATION
Date 01 last calibration:
1
Calibrated opacity -
Calculated oplcity -
Recorded on Ille
Source: optical generator I I
This test recorded on tape#
3 4 5
scr..ns I )
track #
1
2
8
8
.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
OPERATOI'S SIGIIATURE:
DATE:
WITIIESS SIGNA TUftE:
DATE:
Figure VIII-10 Lidar Log Of Operations-Sheet 2
-------
REFERENCES
1.
2.
R.T.H. Collis, Applied Optics 9, 1782 (1970).
R.L. Byer. Optical and Quantum Electronics 7, 147-177 (1975).
3.
M.P. McCormick, W.H. Fuller, NASA Langley Research Center, Lidar
Applications to Pollution Studies.
4.
C.S. Cook, G.W. Bethke and W.O. Conner, Applied Optics II, 1742
(Aug 1972). .-
5.
W.B. Johnson. Jr., Journal of Applied Meteorology 8. 443-449,
(1969) .
6.
E.E. Uthe, Stanford Research Institute, Lidar Observations of
Particulate Distributions Over Extended Areas.
7.
R.G.H. Collis, E.E. Uthe, Opto-E1ectronics 4, 87 (1972).
W.E. Evans and R.T.H. Collis, S.P.I.E. Journal Vol. 8. 38 (1970).
8.
9.
W.B. Johnson, E.E. Uthe. Atmospheric Environment, Vol. 5, 703
(1971) .
10.
E.E. Uthe. C.E. Lapp1e, Stanford Research Institute Report 8730.
Study of Laser Back Scatter by Particulates in Stack Emissions
(1972) .
11.
M.P. McCormick, S.H. Melfi etc., NASA Report TN 0-1703, Mixing
Height Measurement by Lidar, Particle Counter and Rawinsorde in
the Wi11amette Valley, Oregon (1972).
12.
A. Cohen. Applied Optics 14, 2878 (Dec. 75).
13.
W. Viezeg. J. Ob1anas, Journal of Applied Meteorology 8, 369 (1969).
14.
C.E. Lapp1e. E.E. Uthe, Stanford Research Institute, Remote
Sensing of Particulate Stack Emissions, A.I.C.E. Meeting, Aug.
20. 1974.
15.
EPA Report EPA-650/4-73-002 (October 1973). Lidar Studies of
Stack Plumes in Rural and Urban Environments.
-------
145
16.
E.E. Uthe. P.B. Russel, Am. Met. Soc. Bulletin Vol. 55 No.2 (Feb.
1974) .
17.
R.J. Allen, W.E. Evans, Rev. of Sci. Inst. 43, 1422 (1972).
18.
S.H. Melfi, Proceedings, 2nd Joint Converence on Sensing of Env.
Pollutants 73 (1973).
19.
C.S. Cook, G.W. Bethke, General Electric, Co., EPA No. 68-02-0093
(1972) .
20.
EPA Report: EPA-650/2-73-040 (Dec. 1973), Development of Range-
Squared and Off-Gating Modifications for a Lidar System.
21.
EPA Report: EPA/NEIC-TS-128, (Feb. 1976), Field EvaluatiQn of
Mobile Lidar for the Measurment of Smoke Plume Opacity.
22.
23.
C. Werner, Opto-electronics, 4, 125 (1972).
Private Communication, William D. Conner, EPA/RTP, North Carolina
August 1975.
24.
H.C. Van de Hulst, Light Scattering by Small Particles, John
Wiley & Sons, Ie., New York, (1957).
25.
D. Diermendjian, Electromagnetic Scattering on Spherical Polydisper-
sions, Elsevier Publishing Co., New York (1969).
26.
M. Kerker, The Scattering of Light and other Electromagnetic
Radiation, Academic Press, New York (1969).
27.
A.W. Dybdahl, M.J. Cunningham, Utilization of the Omega-1 Lidar
In EPA Enforcement Activities, Proceedings, Symposium on the
Transfer and Utilization of Particulate Control Technology, July
1978.
28.
SRI International Report: Lidar Calibration and Performance
Evaluation (5828-4) (Jan. 1979).
29.
SRI International Report:
5828 (Jan. 1978).
Lidar Optical Signal Generator. Model
30.
American National Standard for the Safe Use of Lasers ANSI Z
136.1-176, 8 March 1976.
31.
U.S. Army Technical Manual TB MED 279, Control of Hazards to
Health from Laser Radiation, February 1969.
-------
146
32.
Laser Institute of America, Laser Safety Manual, 4th Ed.
33.
U.S. Department of Health, Education and Welfare, Regulations
for the Administration and Enforcement of Radiation Control for
Health and Safety Act of 1968, January 1976.
34.
Laser Safety Handbook, Alex Mallow, Leon Chabot, Van Nostrand
Reinhold Co., 1978.
35.
U.S. EPA Visible Emission Inspection Procedures, August 1975.
36.
Guidelines for Evaluation of Visible Emissions, EPA-340/1-75-007,
April 1975.
-------
APPENDIX
Part 60 - Standards of Performance
For New Stationary Sources
Final Rule
Effective Date:
June 22, 1977
-------
Title 28--Judicial Administration
CHAPTER I-DEPARTMENT OF JUSTICE
'[Order No. 72:>-77)
PART Q-ORGANIZATION OF THE
DEPARTMENT OF JUSTICE
Conduct of legal Proceedings
AGENCY: Department or Justice.
ACTION: Final rule. '
SUMMARY: Under 28 U.S.C. 515(a).
Department or Justice att<>rneys, when
sPecifically directed by the Attorney
General, are authorized t<> conduct any
Idnd or legal proceeding, including
grand jury proceedings, which United
states Attorneys are authorized by law Title 38--Pensions, Bonuses, and
t<> conduct, whether or not the attorney Veterans' Relief
is a resident or the district where the CHAPTER I-VETERANS
proceeding is brought. Present regula-
tions delegate certain or the Attorney, ADMINISTRATION
General's authority wlder this statute PART 3-ADJUDICATION
to certain Depart.ment officials. This Subpart B-Burial Benefits
, order broadens the a.uthority delegated
by the .">.ttorney Genern.l eXiJressly to HEARSE CHARGES FOR TRANSPORT.
include the designation of attorneys to . ING BODIES
conduct legal proceedings, and extends AGENCY: Veterans Administration.
the delegation to all Divisions. ACTION: Final Regulation.
EFFECTIVE DATE: May 12, 1977. SUMi\1ARY: The VA has amended its
FOR FURTHER INFORMATION CON- regulation relating to hearse charg-es for
TACT: . ' transporting a body to place of burtal.
John M. Harmon. Acting Assistant At- EFFECTIVE DATE: May 11, 1977.
. . torney General, Office of Legal Coun-
. sel, Department or Justice, Washing- FOR FURTHER lliFORMATION CON-
: ton, D.C. 20530 (202-739-2041>. . TACT: '
By virtue of the authority vested in Mr. T. H. Spindle. Chief. Regulations
me by 28 U.S.C. 509, 510 and 5 U.s.C. Staff, Compensation and Pension Serv-,
301. Part 0 of Chapter I of Title 28, Code ice Veterans Administration, wash-I Title 4O-Protection of Environment
of Federal Regulations, is amended as ing,D.C. 20420 (202-389-3005>' 'CHAPTER I-ENVIRONMEN'fAl
follows:
1. A new ~ 0.13 Is added at the end of SUPPLEMENTARY lNFORMATION: PROTECTION AGENCY
Subpart B, t<> read M follows:' On page 16839 of the FEDERAL REGISTER of [FRL 71:>-8)
Ma~ch 30, 1977, there was pUblished a PART 6O-STANOARDS OF' PERFORM.
~ 0.]3 Lel;al proceedin~s. notIce of proposed regulatory de.velop-t ANCE FOR NEW STATIONARY SOURCES
. ! (a) Each Assistant Attorney General ment to amend ~ 3.1606(b) relatmg t<>
and Deputy Assistant Attorney General hearse charges. When a person dies in a Compliance With Standards and
is authorized t<> exercise the authortt.y Veterans Administration facility to Maintenance Requirements
of the Attorney General under 23 U.S.C. which he or she was properly admittedt AGENCY: Environmenbl Prot€'Ction
515(11.), in cases assIgned to, conducted, for hospital, nursing home or domlcllU- Agency,
handled, or sllpcrvi~ed by such official, ary care Wlder 38 U.S.C. 610 or 611(11.), ", ", '
to designate Department attorneys to the Veterans Administration is usually ACTION: Fin:!.l rule.
conduct any legal proceeding, civil or required w pay the cost of transportingj Sm.IMARY: TIlls action amends the
criminal, including g-r:ll1d jury pro- the body to the place of burial. (38 U.S.C. genernl provisIons of the standards of
ceedlngs and proceedings before com- 903). The Veterans Administration Is pcrfonnance to allow methods other
mitting magistrates, which United States also dlr(~cted to pay the cost of transport- than Reference Method 9 t<> be used :tS a.
attorneys are authorized by law w con- iDg tl~e body of certain veterans who die means of measur1n~ plume opacity. TI1e
, duct, whether or not the deslcnn.ted at- ou!.swe or a Veterans Admlnlstratlonl Environmcnt.f\l Protection Agency \EPA)
torocy Is a resident of the d1<;tr1ct in faci~ty when burial will be made In a Is Investigating a remote sensing lnser
which the proceedln~s Is brought. N:ltlOnal Cemetery. (33 U.S.C. 908) radar system of mc.-'1.Surlng plume opacity
, (b) Each Assistant Attorney ~neral Claims have been received for payment and believes It could IJc considered :1.') IUl
~ authorized to redeJer;a.1.e to Section of ch~rges f~r' transporting a body by I alternatIve method w Reference Method
fEDERAl REGISHR, VOL. 42. NO. 99-MONDAY, MAY 23, 1977
II
RULES. AND REGULATIONS
will be limited to 10 minutes for an oral
presentatioIl' exclusive of tune Wl1Sumed
by Questions from thc panel for the Gov-
enunent and aIlswers tl1ereto.
AD. agenda showing \.!1e:schcduling of '
the speakers will be 'made after outlines
&re received from, the ,speakers, and
wples of the agenda Will be available
free of cha~r;~ at the hearing.
, RoBERT A. BLEY.
DirectCYr. Lcgi..~lation and
Regulatians Di1!'ision.
IFRo Doc.77-14622 Ftled 6-2D-77;8:45 am)
ChIefs the authority delegated by para-
graph (a) of this section, except that
such redelegatlon shall not apply to the
deslgnatton or atwrneys to conduct
grand jUry proceedings. '
S'0.40' [Arnendt'd]
2. Paragraph (a) of 9 0.40 of Subpart
H Is amended by deleting "designation
of attorneys to present evidence to grand
juries."
!i 0.43 [Re\'oked]
3. Sectton 0.43 of Subpart H is
revoked.
S 0.50 [AmC'lIIled] ,
4. Paragraph (a) of 9 0.50 of Subpart
J. is amended by deleting "and desig-
nation of att<>rneys'to present evIdence
t<> grand juries:'
!i 0.60 [HemkedJ
5. Section 0.60 "of Subpart K is
revoked.
(28 U.S.C. 509.510 and 5 U.S.C. 301.)
...pated: May 12, 1977;
GRIFFIN B. BELL, '
Attcn-ney General.
(FE Doc.77-14545 Filed :>-2D-77;8:45 am)
2620j
hearse over quite long distances when
common carrier serv1ce was readily avail-
able. In these claims the hearse charr:es
greatly exceeded the common carrier
rate. Therefore, ~ 3.1606 Is amended to
provide that payment or hearsc charr:es
for transporting a body over long dis- '
tances will be limited t<> prevailing com-
mon carrier rates where It Is reasonable
and customary for shipment to be made
by common carrier. This limitation will
not be for application where common
carner service is unavailable or where use
of a common carrier would clearly be
impractical. 'Vhen a common carrier is
used w transport a body, charges for use
of a hearse t<> deliver the body t<> and
from the carrier will be paid.
Interested persons were given 30 days
in which to submit comments, su-2D-77;8:45 am)
-------
2G'lOG
'\ '9. Tbb amendment would allow EPA to
p.-opose such systems 8.'! alternative
methods In the luture.
EFFECTIVE DATE; June 22. 1977.
FOR FURTHER INFOR1\1ATION CON-
TACT:
Don R. Goodwin, Emission Standard3
and EngIneering Division, Environ-
mental Protection Agency, Research
Trlangle Pnrk. North Carol1na 27711,
telephone no. 919-688-8146, e:"t. 271.
BUPPLD,rENTARY INFORMATION:
As ortg1na.ily expressed, 40 CPR. 60.1Hb)
. perm.1tted the use of Reference Method 9
exclusivelY lor determ1n1ng whether a
,aource compiled with an applicable
opa.city standard. By this action. EPA
:amends ~ 60.11 (b) so that alternative
methods e.oproved by the Adm1n1.5trntor
may be useo. to determlne opacity. ,
When ~ 60.1Ub) was originallY pro-
mu1ga~, the v1sible emissions (Method
II> technique 01 determ.lning plume
opacity with trained v1sible emission ob-
servers was the only expedient and accu-
rate method available to en!orcement
personnel. Recently, EPA lunded the de-
velopment 01 a remote sensing laser ra-
dar system (LIDAR) that appears to pro-
duce results adequate for determ.ln.ation
of compl.1.'Ulce with opacity standards. . Title 45-Public Welfare
EPA 1.5 currently evaluating the equip-
ment and 1.5 considering proposing its . CHAPTER I-oFFICE OF EDUCATIOi'l, DE-
use as an alternative technique of meas- PARTMENT OF HEALTH, EDUCATION,
1lring pl=e opacity. ' ' . AND WELFARE "
Tb1.5 amendment will allow EPA to ,. PART 146--MODERN FOREIGN'
eonslder use of the LIDAR method of LANGUAGE AND AREA STUDIES.
detenn.1n1ng, plume opacity and. if ap- Awards of Grants and Contracts
propr1ate, to approve th1.5 method for en- .
forcement of opacity regulations. If th1.5 AGENCY: Office of EducatIOn, HEW.
method appears to be a suitable aiterna- ACTION: Final re~Jlation.
tlve to Method 9, It will be proposed In ,",.,... , ~ ~ ' .
the F1:D~R..u. REGISTER for public com- SU.p\'~Y. These p..o",?sed regulatIons
ment. Alter considering comments, EPA set ...orth rules 2nd cntena govern1ngthe
wID determine if the new method w11l be , award o~ gra~ts and contracts ro Instltu-
an acceptable means of determining tIon.> 0... higher. education, quallfied
'opacity compliance. orga.nlzatIons and tndividuals for the
, , purpose of providing Federal financial
'eseca. 111, 114, 301 (90). Cle90n AIr Act, 5eC. 4(8.) ~..si.:;tance to establish and operate,
o:r Pub. 1.. 91-604, 84 Stat. 1683; see. 4(0.) of Langua'7e and Area Studies Centers
Pub. 1.. 91-604. IH Stat. 1687; sec. 2 oC Pub. 1.. Co ~
No. 90-14<3, 81 Stat.. 604 (oCI U.s.C. 1857cHl, ; Graduate and Underg!'2.du.:!.te Interna-
1857c-9 a.nd 1857g(o.».) tional Studies Programs, for the award
, " ~ of fellow.sh.1ps to Individuals undergoing
NcmL-Economlc Impact Analysis: The, trnin.b:1g in any center or under any pro-
Zllvlronmental Protection Agency ba.s deter- "7= receiving Federal financial ass1.5t-
m1ned tho.t this actIon does no.LcontAln a' b - ~
zru.Jar prop<:»al ~qu1r1ng preparo.tlon oC an a.rlce under the ND~"" Act, and for
1:oonomlc Impact ADalyo1a under Executive research and studies.
Orders 11821 a.nd 11949 a.nd OMB Circular , EFFECTIVE DATE P t to t.
.A-I07. ' , ....: ursuan sec IOn
431(d) of the Gencr3.1 Education Pro-
visions Act, as amended (20 U.s.C. 1232
(d) ), th1.5 regulation has been trans-
mitted to the Congress concll...'Tently with
ft..s publication In the F1:DERAL REGIST'E:R.
That section provides that regulations
subject thereto shall become effective on
the forty-filth day following the date of
such ~n~mk~lon, subject ro the pro-
V'.s1ons therein conCerning Congressional
action and adjournment.
(I) Compl.1anoe with opacity stand- DATES: None.
a..-d's in th18 part shall be determ.tDed by ADDRESSES: None.
. ,,' Dated: May 10, 1977.
. ".. ..' . ."
, " ":" DoUCIAS M. COSTLE,
, Adrrnnutrctor.
" I
Part 60 or Chapter I. Title 4{) ol the
Code at FcdCrnl Regulations 1.5 amended
~fonows:
L Sec~on 60.111.5 amended by revising
p:I.rngT1\ph (b) as follows:
I ~ll Comprunr.e with 8t:\ndanb and
_intcnancc requirements.
. . . .
.
RULES ArJD REGULATIONS
conducting observations In accordance
with Reference Method 9 In Appendl.'t A
of thJs part or any alternative method
that 1.5 approved by the Admln1.5trator.
Opacity readings of portions of plumes
which contain condensed, uncombined
water vapor shall not bc used for pur-
pooes of determining compliance with
opacity standards. The results of con-
tinuous monitoring by transm1.5someter
which 1.ndi~te that the opacity at 'the '
time visu:JJ observations were made was
not In excess of the standard are proba-
tI...e but not conclusive evldcnce of the
actu.:ll opacity of an e:nlsslon. provided
th::J.t L'le source shall meet the burden 01
proying that the Instrument used meets
(Ilt the time of the alleged vlol:J.t1ont
Performance Specification 1in Appendix
, B of L'l1.5 part, has been properly main-
tained and (at the ttne of the alleged
violation) C2.ilbrated, and that the
resulting data have not been tampered
with L'1 any way.
FOR FURTIIER INFORMATION CON-
TACT:
, -
Edward L. Meador, Dtv1.5lon of Inter-
nntIon3.1 Education. 7th and D Streets,
SW ~ Room 3907. Reg1on3.1 Office Build-
ing #3, Washl.ngton, D.C. 20:!02 (202/
,245-9~~1) ,
- SUPPLElI.rENTARY INFOP.J-.BTION:
TIie Natlon3.1 r)cfense Education Act a!
1958 in Its statement of find1n::;:> and
declaration of pOilcy says. "The Con;:n-css
finds and declares that the security of the
Nation requlres the fuilest development
of the mental resources and technIcal
skills of its young men and women. The
present emergency demands that addi-
tional and more adequate educational.
opportunities be made avaUable. The de-
fense of th1.5 Nation depends upon the
mastery of modern techniques developed
from complex scientific principles. It de-
pends as well upon the discovery and
development of new principles. ne... tech-
. . Diques, and new knowledge." '
(Sees. Ill, 114. 301(0.), Cle9o!:l Air Act, Sec. ~ (20 U.s.C. 401.)
(a) or Pub. L. 91-60-1. 84 Stat.. 1683; sec. ~(o.) The importance' ,of a knowledae of
or Pub. L. 91-604. 84 Stat. 1687; sec. 2 of Pub. - f i I d t d. "th
1.. ~o. 90-148 81 Sta.t. 504 (42 U.S.C. 1857c-6, ore go anguages an area s u les to e
1857c-9. 1857g(o.».) a.ttalnment of th1s policy w:!.S recognized
, by the inclusion In the Act of Title VI.,...
(FR Doc.77-14562 FIled &-20-77;8:45 o.m) Modern Foreign Language and Axea
Studies. Th1.5 Title authorizes: Federal
financial ass1.5tance to i.nstltutIons of
higher educati9D for the establishment
and operation of Inter.:latlon3.1 Studies
Centers and for Graduate and Un-
dergraduate Intern::J.tlonal Studies Pro-
grams, fellowships for graduate students
In foreign language and area studies, and
Federal financial. assistance to pubUc
and private agencies, org:mizations and
institutions as well as individuals for
research in the area of foreign language
and area studies. -
"The Internation3.1 Studies Centers
Program" pro.ides grants to higher edu-
cation institutions or cocsortla of such
institutions to establish and operat~ cen-
ters focusing on one world region. These
centers offer instruction in two or more
of the area's principal lang-u".ges and In
other disciplines in orde-r to provide
training In understanding that particular
world area. Other centers that feature
instruction in compar::J.tive : approaches '
to topics of ,concern.. to: .more-. th:).n one:
nation, internatIon.:l.l rel:ltionS. or 'inter-
reg10nal studies are 0.1.50 eligible fo.r sup~
port. Awards are available in each cate-
gory to centers having a'co.mbinatlon of
graduate and undergraduate instruction
(unless undergraduate Instruction is not
offered) as well as to those offering only
undergraduate training. '
"The Graduate and Unden::r::J.duate in-
ternational Studies PrOgramS" may pro-
yide grants of up to t~,o years. or in cer-
tain instances 3 Ye3.rs, ro hig-her educa-
tion 1n.stltut!ons or consortia of such
institutlo!lS to est....bl1.5h Instructional
programs In internation.:U studies at the
gradu.:!.te or undergraduate levels. Pro-
grnm.s must be global or multl-area in
instructional. coverage. wGraduate Ir\ter-
FEDERAL REGISTER, VOL 42, NO. 99-MONDAY, MAY 23, 1977
-------
|