NEIC
ALTERNATE METHOD TO REFERENCE METHOD 9
ALTERNATE METHOD 1 - DETERMINATION OF THE
OPACITY OF EMISSIONS FROM STATIONARY
SOURCES REMOTELY BY LIDAR
v>EPA
national enforcement investigations center
denver federal center bldg 53. box 25227 denver, co 80225

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Environmental Protection Agency
Office of Enforcement
ALTERNATE METHOD TO REFERENCE METHOD 9
ALTERNATE METHOD 1 - DETERMINATION OF THE
OPACITY OF EMISSIONS FROM STATIONARY
SOURCES REMOTELY BY LIDAR
National Enforcement Investigations Center
Denver, Colorado

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PROPOSED ENVIRONMENTAL PROTECTION AGENCY NEW METHOD FOR
STANDARDS OF PERFORMANCE FOR STATIONARY SOURCES
ENVIRONMENTAL PROTECTION AGENCY
(40 CFR Part 60)
Proposed New Alternate Method to Reference Method 9
On December 23, 1971, the Environmental Protection Agency promulgated
standards of performance for five categories of stationary sources under
Section III of the Clean Air Act, as amended. An appendix to the regulation
contained Reference Methods 1 through 9, which detailed requirements for
performance testing of stationary sources. Since the promulgation of these
reference methods EPA has continued to participate in the development of
new, improved and/or supplemental methods that will permit the quantitative
monitoring of stationary source emissions remotely (non-contact methods),
quickly, easily and with a high degree of accuracy during both day- and night-
time hours. A new test method has been developed from a detailed evaluation
of scientific remote sensing instrumentation for the determination of station-
ary source emissions (plume) opacity.
This new method (Alternate Method 1) employs a lidar (lasar radar) which
is an optical system installed in a truck-mounted van enclosure. This mobile
lidar is specifically designed and fabricated for measuring the opacity of
visible emissions from a given stationary source during both day- and night-
time ambient lighting conditions. The laser transmitter within the lidar
emits a short pulse of light. The lidar receiver collects the laser light
backscattered from the atmospheric aerosols before and beyond the visible
plume as well as that from the aerosols (particulates) within the plume.
The lidar receiver converts the backscattered optical signals to electronic
signals or data. From the data (just before and beyond the plume) the plume
opacity is subsequently calculated and printed in hard copy format along
with the date and time to the nearest second. The nominal data gathering
rate of the lidar is an opacity measurement or determination once every 10
seconds.

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This rate can be maintained in continuous operation for minutes or even
hours. The lidar has an inherent data processing capability that calculates
the opacity values, subsequently records these opacity values in hard copy
form, and also records the original lidar receiver data (signal amplitude vs
range) on magnetic tape for future reference or use. This method is intended
for use during night-time hours as it is during the day. This is a most impor-
tant capability in the measurement of stationary source emissions opacity.
By this notice, the Administrator is inviting comments on the proposed
new test method. Submittals should, wherever possible, be supported with
data and calculations.
Comments on the proposed new test method should be submitted, in trip-
licate, to the National Enforcement Investigations Center, U.S. Environmental
Protection Agency, P. 0. Box 25227, Denver, CO 80225, Attention: Mr. Arthur
W. Dybdahl. All comments post-marked no later than	1980, will be
considered.
Copies of comments received will be available for public inspection
during normal business hours at the Public Information Reference Unit (EPA
Library), Room 2922, 401 M Street, S.W., Washington, DC.
This new test method is proposed under the authority of Section III of
the Clean Air Act, as amended (42 U.S.C. 1857c6)
Dated:	, 1980
Administrator
It is proposed to amend Part 60 of Chapter I of Title 40 of the Code of
Federal Regulations by adding Alternate Method 1 to Reference Method 9 as
follows:

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ALTERNATE METHOD TO REFERENCE METHOD 9.
ALTERNATE METHOD 1 - DETERMINATION OF THE OPACITY
OF EMISSIONS FROM STATIONARY
SOURCES REMOTELY BY LIDAR
Many stationary sources of air pollution discharge particulate emissions
into the atmosphere as visible emissions usually as a plume emitted from a
stack or other source structure. This proposed method provides the quantita-
tive determination of the opacity of an emissions plume remotely by a Mobile
Lidar System (laser radar; Lujht Detection and Ranging). The method includes
procedures for the calibration of the lidar and procedures to be used in
the field for the lidar determination of plume opacity. The lidar is used
to measure plume opacity during either day- or nighttime hours since it
contains its own optical energy source or transmitter. The operation of
the lidar is not dependent upon ambient lighting conditions (light, dark,
sunny or cloudy).
The most common laser transmitter is the ruby laser which emits red
light at 6943 Angstroms. The ruby laser has been chosen for the following
reasons:
The red light 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 slight-
ly less for red light than for that measured with green or white
1ight.

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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 monitored
with the ruby laser.
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 method apply only to
a ruby lidar. These tests were performed using the EPA-NEIC Omega-1 lidar.
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 length) of light toward a visible emissions plume.
This light pulse is partially backscattered to the lidar receiver by aero-
sols (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 backscattered light signals from regions (1) and (3), corrected
for 1/R2 fall-off (optical backscatter signal amplitude decrease as a func-
tion 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 measures the square of the optical transmittance (Tp2) of the
plume. The square of the plume transmittance is measured because the lidar
pulse effectively passes through the plume twice. The lidar pulse goes out
through the plume and subsequently is backscattered by the atmospheric aero-
sols beyond the plume [region (3)]. This backscatter signal then returns
through the plume to the lidar receiver.

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3
The backscatter signals are converted to electronic signals in the
lidar receiver. These signals are directed into the data processing intru-
2
mentation which calculates the square of the plume transmittance (T ), the
plume transmittance (T ) and then the plume opacity, 0 , 0 = 1 - Tp. The
opacity value for each lidar measurement or firing is permanently recorded
in a hard-copy format along with its respective date and time data. The
original lidar receiver data (optical backscatter signal amplitude vs. lidar
1ine-of-sight range) along with date, time, source identification, etc. are
recorded on the system's computer-controlled magnetic tape recorder for
future reference or additional calculations.
The most important advantages of the lidar for field use are:
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 during nighttime
hours as well as during daylight conditions, which cannot
be effectively accomplished with the Reference Method.
Its inherent capability of measuring plume opacity with
consistent accuracy and nonsubjectivity independent of back-
ground light contrast conditions such as between a plume
and clear sky, cloudy sky or terrain background, etc. The
color contrast between the plume under test 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 con-
ditions.

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4
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 signifi-
cant negative bias and negative errors inherently associated with the refer-
ence 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.
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; however, with the lidar
mechanism this is not the case.
Under less-than-ideal background-to-plume color/luminiscent contrast
conditions the reference method cannot be effectively used to verify the
data obtained with this method because of the significant negative bias and
negative 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
transmissometer, 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 stand-
ards now require on-stack transmissometers to measure opacity).
The calibration tests showed that the lidar (used for these tests)
measured opacity with an overall accuracy of 0.2% (standard deviation = 0.6%
for 2,880 data values) in the linear channel over the opacity range of 0 to

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5
80% (nominal), and from -0.3 to +0.1% (standard deviation = 0.5% for 1,950
data values) in the logarithmic channel from 20 to 80% (nominal). The in-
ternal calibration mechanism (optical generator in the 0mega-l Lidar) used
to calibrate the lidar in the field was employed for these tests (Reference 5.1).
The 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 Method 9 requirements. 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. 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 1ine-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 (Section 2.4.3
of this Method).
The calibration and performance evaluation tests clearly demonstrate
that the lidar is an acceptable alternate method. The required correlation
(performance evaluation tests) was not carried out with visible emissions
observations, due to the inherent negative bias, but with the smoke genera-
tor's white-light transmissometer which is routinely used to certify the
visible emissions observers under the reference method.
The operation of the lidar in the field is performed in accordance
with stringent laser safety standards which EPA developed using the refer-
ences given in Section 5, as a basis (Section 7 of Reference 5.1).
1. Principle and applicability
1.1 Principle. The opacity of visible emissions from stationary
sources (stacks, ducts, etc.) is measured remotely by a mobile
lidar (laser radar).

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1.2 Applicability. This method is applicable for the remote
measurement of the opacity of visible emissions from station-
ary sources during nighttime as well as daylight conditions,
pursuant to 40 CFR § 60.11(b). It is also applicable for the
calibration of the mobile lidar for the measurement of the
opacity of emissions. A performance/design specification for
a basic lidar system is also incorporated into this method.
Procedures. The mobile lidar calibrated in accordance with Para-
graph 3 of this method shall use the following procedures for
remotely measuring the opacity of stationary source emissions:
2.1 Lidar position. The lidar shall be positioned at a distance
from the source-under-test, sufficient to provide an unobstruc
ted view of the source emissions. The source-under-test must
be at a range greater than the lidar's transmitter/receiver
convergence distance along the line-of-sight or field-of-view.
The lidar observations shall be carried out in such a way
that a good quality, clear air (atmospheric backscatter) re-
turn signal, being free of obstructions, is obtained along
the lidar's line-of-sight before reaching the plume (near-
region) and beyond the plume (far-region). These two signal
segments are used to calculate the plume opacity for each
lidar measurement. When there is more than one source of
emissions in the immediate vicinity of the plume under test,
the lidar shall be positioned so that the lidar beam passes
through only a single plume, free from any interference of
the other plumes for a minium of 50 meters on each side of
the plume under test along the line-of-sight. The lidar shall
be positioned so that the lidar line-on-sight is nearly per-
pendicular to the direction of horizontal drift of the plume,
to the extent practicable. This practice will keep the lidar
line-of-sight distance through a plume equal to the actual

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7
plume thickness, at the point of testing within the plume.
The lidar shall be in a position so that direct solar radia-
tion is not permitted to enter the optical receiver.
When measuring the opacity of emissions from rectangular
outlets (e.g., roof monitors, open baghouses, noncircular
stacks, etc.) the lidar shall be placed in a position so
that the line-of-sight is approximately perpendicular to the
longer (major) axis of the outlet as practicable.
2.2 Lidar observations and measurements. Once placed in its
proper firing position, the lidar shall be aimed (by aiming
telescope) and fired immediately below the outlet of the
emissions source in order that the range to this source be
measured and recorded, and to assure that the lidar trans-
mitter beam diameter at the source range is less than the
source (outlet) diameter. The lidar transmitter beam dia-
meter must be less than the plume diameter at the particular
point or location of test, to conduct the remote opacity
measurement. This determination is accomplished in two ways.
First the operator shall directly view the reflected lidar
pulse through the receiver telescope for complete spatial
coincidence and by a lidar opacity calculation which will be
100% (opaque source structure) if the beam diameter is less
than the plume diameter. Secondly, the lidar beam diameter
shall also be calculated as the mathematical product of two
parameters; namely, the inherent beam divergence angle and
the lidar range to the stack under test. If the lidar beam
diameter is larger than the diameter of the plume under test,
then the instrument must be moved closer to the source until
the above condition is fulfilled.

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8
The lidar is then aimed and fired with the 1ine-of-sight
near the outlet height and rotated horizontally in an upwind
direction to a position clear of the source structure and
the associated plume (if wind conditions are calm, then the
lidar may be moved to either side of the plume that is free
of obstructions). This lidar data signal is the clear-air
return or reference signal. The lidar operator shall inspect
this signal on the oscilloscope display to determine if the
lidar line-of-sight is free of obstructions, obtain a measure
of the integrity and homogeneity of the clear air in front
of and behind the source/plume, and to verify that the source/
plume under test is free from interference from other plumes,
for a minimum of 50 meters on each side of the plume under
test along the line-of-sight, that may be in the immediate
area. This clear-air (backscatter) signal shall be recorded
on magnetic tape and shall be used in the plume opacity calcu-
lations. The frequency of the reference measurements is
established in the Temporal Criterion of Section 2.2.3 of
this method.
Finally, the lidar is aimed at the region of the plume which
displays the greatest opacity, where condensed water vapor
is not present. The lidar is fired through the plume so
that the lidar operator may make any final aiming adjustments
and choose or verify the proper locations of the backscatter
signal segments used in the opacity measurement. When that
is completed, the lidar is placed in operation with the nominal
pulse or firing rate of 6 pulses-per-minute (pulse/10 seconds
as safety permits). The lidar operator shall observe the
oscilloscope display to monitor lidar performance and the
quality of the plume data signals. (The display provides a
near real-time means of determining the quality and integrity
of the near- and far-region atmospheric backscatter signals

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9
used in calculating plume opacity). These plume data signals
are recorded on magnetic tape as a permanent record. The
plume data signals recorded from lidar start to stop is called
a data run. Short term stops of the lidar to record addition-
al reference measurements do not constitute the end of a
data run if lidar operations for a given plume are resumed
within 60 seconds after the reference measurement has been
recorded.
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 cha-
racteristics and variability of the source emissions. The
lidar data rate is nominally maintained at one opacity mea-
surement every 10 seconds throughout a given delta run.
The lidar will be used to measure the opacity of hydrated or
so-called steam plumes. (To the extent practicable the lidar
operators should have technical information with them regard-
ing the respective process and the control equipment for
each stationary source to be listed.) As listed in the refer-
ence method there are two types, i.e., attached and detached
steam plumes.
2.2.1 Attached Steam Plumes: When condensed water vapor is
present within a plume-under-test as it emerges from the
emission outlet, the opacity measurements 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 shall then aim the lidar transmitter/receiver into

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10
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 high-
est opacity. (A high intensity spotlight, night vision scope,
or low light level TV, etc., can be used to aid the lidar
operator in aiming the transmitter/receiver at night).
The lidar operator scans the transmitter/receiver, with the
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
much lower. If the residual plume also has a 95 to 100%
opacity then the lidar operator shall also 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, especially at
night. 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 shall then be
scanned approximately perpendicular to this axis in order to
locate the region of highest opacity. Plume opacity shall
then be measured at this location within the plume. Adjust-
ments are made to this location of the lidar 1ine-of-sight
within the residual plume as deemed necessary by the lidar
operators to correct for changes in wind direction, etc.
The distance from the stack to the position within the plume
where these opacity measurements are collected shall be ob-
tained by a calculation using the lidar range to the stack,
the lidar range to the plume monitoring position, and the

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azimuth/elevation angles between the stack and the plume
monitoring position or point. The geometry for this calcu-
lation, along with the respective variables, is defined in
Figure AM1-1.
This distance is calculated by using Equation AM1-1.
2 2
R.. = [R +R -2R R (Cos p Cos p Cos i|> (AM1-1)
SiJ> L p s	ps	Kp
+ Sin p Sin p ]2
p	s
The variables Rs, Rp, Ps, and ip are measured directly
with the lidar. The three angles are measured on the trans-
mitter/receiver mount by using an inclinometer and a protrac-
tor. The two range values are calculated from the respec-
tive backscatter signals. R^^ shall be calculated and record-
ed for each postion of the lidar line-of-sight while the
tests are being conducted.
2.2.2 Detached Steam Plumes: When the water vapor in a hydrated
plume condenses and becomes visible at a finite distance
from the stack or source emission outlet, the opacity of the
emissions shall be 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.
During daylight hours the lidar operator can visually deter-
mine if the steam plume is detached from the stack outlet.
At night a high intensity spotlight, a night vision scope,
low light level TV, etc. can be used as an aid 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

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12
2
(plume measurement position)
Lidar Position
Projection of '
onto the xy-plane
Projection of Pp onto
the xy-plane
The mathematical variables or functions are defined as follows:
= the range from the emissions point, P , to the plume monitoring
point or position, P .
R$ = the range from the lidar to the source or stack outlet.
= the elevation angle of the lidar 1me-of-sight above the horizontal
plane, to the stack outlet.
Rp = the range from the lidar to the plume monitoring point.
B = the elevation angle of the lidar line-of-sight above the horizontal
plane, to the plume monitoring point.
i|> = the azimuthal angle, in the horizontal plane, of the lidar line-of-sight
measured from the y-axis which contains the lidar and stack outlet.
P (R , 0, 6 ) = Coordinates of the stack outlet in the spherical coordinate
system.
P_(R , B ) = Coordinates of the plume monitoring point in the spherical
p	P coordinate system.
Figure AM1-1. Geometry of the Residual Plume Measurement with Lidar

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13
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, 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 shall subsequently be
measured at this location. Adjustments are made to the loca-
tion of the lidar's 1ine-of-sight within the plume as deemed
necessary by the lidar operators to correct for changes in
wind direction, air temperature changes, etc. The location
of the lidar's 1ine-of-sight within the plume is recorded
for each position while the tests are being conducted.
In the measurement of plume opacity from a sulfuric acid
manufacturing facility, the lidar 1ine-of-sight shall be
positioned within the most-dense part of the plume which
will not necessarily be at the emissions outlet. The charac-
teristic sulfurous gas absorbs plume moisture forming sulfuric
acid aerosols in the submicron size range. High values for
the opacity can occur. Often the aerosol plume does not
become visible for a few stack diameters away from the emis-
sions outlet. This does not constitute a detached steam
plume and shall not be treated as such.
2.2.3 Temporal Criterion for Reference Measurements. This criter-
ion describes how often and under what conditions additional
reference (clear air) measurements are to be obtained.
A reference measurement is obtained with the lidar and record-
ed on magnetic tape within a 60-second time period prior to
any given plume opacity data run. Another reference measure-
ment is obtained within 60 seconds after the completion of

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14
the same data run. This is standard operating procedure
irrespective of the variability of the local atmospheric
conditions along the lidar's 1ine-of-sight.
The reference measurement shall be obtained by directing the
lidar's 1ine-of-sight near the emission's outlet in height
or elevation, and rotated horizontally in an upwind direction
to a position clear or free of the source structure and the
associated plume. If wind conditions are calm, then the
lidar 1ine-of-sight may be moved to either side of the plume
that is free of obstructions.
The need for an additional reference measurement(s) is a
function of local atmospheric kinetics which is usually deter-
mined through the judgement of the lidar operators as they
observe localized meteorological conditions and the character-
istics 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 direc-
tion 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, ob-
serves a noticeable change in the amplitude variations in
either the near- or far-region backscatter signal segments
(not due to a common change in plume opacity) that remains
present for three plume data records (about 30 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 measurement shall
be recorded on magnetic tape). Then the data run shall be
immediately resumed and continued through completion. This

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15
process of obtaining additional reference measurements may
be iterated as many times as required. If the ambient (clear
air) conditions along the lidar's 1ine-of-sight are continual-
ly changing significantly, then reference measurements and
plume data measurements are usually recorded alternately.
During the subsequent analysis of the lidar data, the refer-
ence and data measurement signals shall be analyzed in the
same sequence that they were recorded in the field.
Section 2.1 of this method requires that the lidar shall be
positioned so that the lidar 1ine-of-sight is nearly perpen-
dicular to the direction of the horizontal drift of the
plume, to the extent practicable. If, during the course of
a data run, the direction of drift of the plume changes by
30° or more, as observed from the lidar positions, and if
the lidar 1ine-of-sight is more than about 3 source diameters
from the sources outlet while recording plume opacity data,
then the operation shall be momentarily interrupted. The
parameters Rx, R2 and a of the Elevation/Azimuth Angle Cor-
rection Criteria [Section 2.4.4 of this Method] shall be
measured and the respective backscatter signals recorded on
magnetic tape. Rx and R2 shall be obtained from the plume
backscatter signals, measured at the center of each plume
return spike [Figure AMl-4(b) of Section 2.4.1].
Usually the need to measure these parameters is conincident
with the need for another reference measurement.
2.3 Field Records. The lidar operator shall assign a control
number in the lidar logbook for each independent source under
investigation even if more than one source is located within
the same industrial facility [Figure AM1-2]. This assigned

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Ill) AH I0(. HUNT II01 M UK Kit TAIULATION (rnni )
lAssijn i CONTROL NUMBER to each individual source undar test)
LIDAR LOC CONTROL NUMBER TABULATION
Log RooL Number-	
(Assign a CONTROL NUMBER to each individual source under test]
CONTROL
NUMBER
CONTROL
NUMBER
DATE
ASSI6NED
PROJECT
CITY, STATE
DATE
ASSIGNED
PROJECT
CITY. STATE
continued on next page
Next Log Book Numtm-
Figure AM1-2 Lidar Log Control Number Tabulation
en

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17
control number shall also be recorded on magnetic data tape
for each measurement. (All respective lidar data and reports
shall have the control number recorded therein.) The name
of the facility, type of facility, emission source type and
official designation (stack, open baghouse, etc; stack 001,
etc.) and the geographic location of the lidar with respect
to the source under-investigation shall be recorded in the
lidar logbook [Figure AM1-3]. The date of the test and the
time period that a given source was monitored shall also be
recorded in the logbook. The 1idar-measured vector (emissions
source range and angle referenced to magnetic north) and
plume characteristics also are recorded in the logbook. The
wind speed, wind direction, air temperature, relative humidity,
barometric pressure, visibility (measured at the lidar's
position) and cloud cover are recorded in the logbook at the
beginning and end of each time period for a given source.
A small sketch shall be recorded in the log book depicting
the location within the plume of laser beam incidence.
The parameters 0 , p and t|i, defined in Figure AM1-1, shall
s p
be measured at the lidar transmitter/receiver mount and
recorded in the log book for each source and for each measure-
ment position or location within a given plume under-test.
Also the parameters a, Rx, and R2, defined in Section 2.4.4
of this method for the Elevation/ Azimuth Angle Correction
Criterion, shall be recorded in the log book for each source,
each measurement position or location within the plume and
for each instance when the plume drift angle is measured.
In addition to the assigned control number, the date, time
(to the nearest second) of each measurement, the source ident-
ification, the video channel used (linear/ logarithmic channel,
for example), the digitizer's sample interval and the location
or address of the clear-air reference signal on the magnetic

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Facility aaaa tad UcatUa
IIDAH LOC OF OPERATIONS
Control number. 0 VIH. A -
LIDAR OPERATOR S NOTES
| lac I u d • politico ol luir bun within plum-- attached plgao, etc )
At lit field illt • • II	fto«	••	 (••«¦! !'¦•)
locailoe of LIDAR
Ok«ctian to source	 Range to souict 	 km
later inclination [~ angle is up horizontal is 0°| 	
Soorco IfM o«d official datlgMolloa
Hobo (horoitorlltlci (color, ibopo, ilooa proioat, alf )
Wlod ipood basin	hm/hr and	km/hr WI¦ d diroitloi begin	and	
Air loaptrotoro t>sgin 	°C end 	° C lolotlio hialdlty begin 	 % end 	%
laioaitar begin	end	Vlilblllir begin 	km end	km
Clootf io»«i begin	end
Dot* nurdi aodo It Held (topoi, prlotooti, photo I, ole )
MAGNETIC TAPES
tapes luckn lilts
t ID * t fUNCTIOH >HIM(ATI0H	Source optical generator I ) scream I I
Data of lait calibration 	This tait recorded on tap*#	tracks 	
1 2 3 4 5 1 7	8
Calibrated opacity 	 	 	 	 	 	 	 	
Calculated opacity 	 	 	 	 	 	 	 	
Recorded on III* 	 	 	 	 	 	 	 	
OPftATOft'S StGMATUtt	DATI 		OPIIATOl'S JISHATUI1	DAT! 	
WITMSS SIGNATUKI 	DAII 		WITNISS SIONATUII 		 DATI: 	
I—'
Figure AM1-3 Lidar Log Of Operations	00

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19
data tape shall be recorded on the magnetic data tape for
each lidar measurement.
If a detached or attached steam plume is present at the emis-
sions source under-test, this fact shall be recorded in the
lidar logbook along with the quantitative data depicting
where in the plume the lidar measurements were conducted
[Equation AM1-1].
Each magnetic tape used to record field and calibration
data signals shall be assigned a number and that number
recorded in the lidar log book.
2.4 Lidar Data Reduction and Records. The lidar data shall be
analyzed by computer at the time of each lidar measurement
or having been recorded on magnetic tape, shall be analyzed/
verified at a later time. The opacity value and the associ-
ated statistics of the emissions from the respective source
under-test shall be computed and recorded along with the
time and magnetic data tape address for each measurement.
2.4.1 Opacity Calculation and Data Analysis. Referring to the
lidar signal amplitude vs. lidar range traces in Figure AM1-4,
the opacity value (Op) for each lidar measurement is calculated
using Equation AM1-2.
0p = 100%
(AM1-2)
where:
I = near-region signal amplitude, plume data
signal, 1/R2 corrected,

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20
Convergence Point
\
(flat)
(negative slnn^
(exaggerated)
ZeroSmna^
Level	Lidar Range Or Time
(a) Clear-air reference measurement made near the plume in order to
account for the prevailing non-ideal atmospheric conditions. The
signal is 1/R2 corrected
Plume
Spike
(Near Region)
(Far Region)
	 Signal
Plume
Lidar Range Or Time
(b) Lidar return (plume data) signal showing the effect of plume
attenuation on the backscatter signal in the far region
The signal is 1/R2 corrected.
1 Nanosecond-10"® Seconds.	Range=Speed of Light Time/2
()=Pick interval 100 nanoseconds in length
Figure AM1-4 Traces Of Lidar Backscatter Signals

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21
1^ = far-region signal amplitude, plume data
signal, 1/R2 corrected,
Rn = near-region signal amplitude, clear-air
reference signal, 1/R2 corrected, and
R.p = far-region signal amplitude, clear-air refer-
ence signal, 1/R2 corrected.
The lidar backscatter signal traces shown in Figure AM1-4
are corrected or mathematically compensated for the 1/R2
signal amplitude decrease, where R is the lidar range func-
tion. This decrease is inherent to the laser energy signal
backscattered from particles and aerosols in the atmosphere.
This correction must be performed on each backscatter signal
before plume opacity can be calculated. Since in lidar terms,
range and time differ only by a constant, one-half the speed
of light, the 1/R2 correction for the amplitude decrease may
be done in the time domain ( j^2 * R2 = 1, ^2 ' t2 = D- R =
c t/2, where R is lidar range depicted in Figure AM1-1, c is
the speed of light being 2.9979 • 108 meters/ second and t
is lidar time measured from the time the laser was fired,
t .
0
The 1/R2 correction mechanism for a backscatter signal is
depicted in Figure AM1-5. This backscatter signal having
been converted to an electronic signal through the optical
detector or photomultiplier tube, was converted from an ana-
log electronic signal to a digital electronic signal by a
high speed digitizer, necessary for computer processing.
This digital signal is comprised of many short segments or
time intervals. (On the oscilloscope display the digital
signal would appear to the operator identical to the analog

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Lidar Range Or Time
Antp < A2 due to atmospheric extinction
R=ct/2, R2=c2t2/4,
(1/R2) R2 = 1 £il2 = (1/t2) t2=1
c2t2 4
4
2
Figure AM1-5 1/R Correction Mechanism

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23
signal if it were displayed.) The length or size of these
time intervals is selected in the digitizer by the operator.
The standard size for the time (sample) interval in this
application is usually 10 nanoseconds.
Each time interval in the digital signal, beyond or later in
time than t , is subjected to the 1/R2 correction. The signal
amplitude, An> of the nth time interval is multiplied by the
square of the time, elapsed from t , defining that interval.
In Figure AM1-5, the uncorrected signal amplitude, An is
multiplied by the square of the time of the nth interval,
t , yielding Antn2, the corrected amplitude. This process
is carried out for each time interval in the backscatter
signal producing a 1/R2 corrected signal.
In Equation AM1-2, I , I -, R and R* are each chosen by the
n f n f
lidar operator or data analyst. I and 1^ are 100 nanosec
in length [Figure AM1-4]. The value of I must be, in time,
within the interval chosen for R , and I- must be within
n	f
that for Rf. The lengths of Rn and Rf shall be 100 nanosec
minimum.
I and R are the plume data and reference pick intervals
n n	K	K
for the near region of the lidar backscatter signal, and 1^
and are the respective pick intervals for the far region
[Figure AM1-4].
The criterion for the selection of the pick intervals is
best described by example. Figure AM1-6 shows 3 actual
lidar backscatter return signals which were plotted by com-
puter from a field data tape. Figure AMl-6(a) is the 1/R2-
corrected clear air reference backscatter signal recorded
for use in calculating the plume opacity from the plume
signal [Figure AMl-6(b)]. These signals contain slight

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24
Convergence Point
/
(Near Region)
(Far Region)
12 10 38

(a) Reference Signal, 1/R Corrected
Plume Spike
12 25.59
(b) Plume Data Signal, 1/R Corrected
Plume Spike
-Atmospheric Backscatter Noise
Area 1
(c) Plume Data Signal, 1/R Corrected
Area 2
NOTES: (l) 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, l/R2-Corrected, showing slight atmos-
pheric noise. This reference signal is for (b). R^, R^ are chosen as
indicated coincident with In, 1^.
(b)	Lidar-return Video Signal, l/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.
I , L are chosen as indicated,
n f
(c)	Lidar-return Video Signal, l/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> 1^ are chosen as indicated.
Figure AMI - 6. Computer Plots of Lidar A-Scope Backscatter Signals

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25
atmospheric backscatter noise as observed in the ripple or
variations in amplitude to the right of the point o'>: conver-
gence. The near-region pick interval, In, is chosen as
close to the plume as practicable with the signal quality
in the chosen interval being of minimum overall amplitude
and minimal amplitude variation. The reference signal pick
interval, R , must be chosen for the same time interval as
n
I as depicted in Figure AMl-6(a,b).
The far-region pick interval, If( is also chosen as close
to the plume's far side as practicable. The quality of the
backscatter signal in this chosen interval is of minimum
overall amplitude and minimal amplitude variation. The far-
region reference signal interval, R^, must be chosen over
the same interval as 1^ [Figure AMl-6(a,b)].
Figure AMl-6(c) is a computer plot of a lidar backscatter
return signal showing significant levels of atmospheric
backscatter noise in the near-region which was due to fugi-
tive dust blowing in. front of the lidar. In this case there
are only two areas in the near region where the pick interval,
1^, can be selected, i.e., areas 1 and 2 as shown. The
average signal amplitude over the 100-nanosecond time inter-
val in each of these two areas is the same. However, in
applying the above criterion, Area 2 is the best interval
to be used for the plume opacity calculation (the respective
reference signal is not shown). The far-region pick inter-
val, 1^, is chosen as shown in Figure AMl-6(c) according to
the criterion. Any desired pick interval, such as areas 1
and 2 in Figure AMl-6(c), that is not 100 nanoseconds wide
shall not be used in the opacity calculation. If no such
interval exists in the near-region or the far-region then
the plume backscatter signal shall not be used for the opac-
ity calculation. Many additional field-oriented examples of
pick interval selection are available in Reference 5.1.

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26
Once the pick intervals have been chosen, the respective
amplitudes or values of each is calculated. The amplitude
of I shall be calculated by the average of the individual
amplitudes of the 10 equal time segments or intervals (usual-
ly 10 nanoseconds) that comprise the respective pick inter-
val (100 nanoseconds in length) according to Equation AM1-3.
1 m
]n = £ 1	(AM1-3)
n m .	^ i
where:
I.j	= the amplitude of the ith segment or interval,
I	= sum of the individual values,
m	= number of segments in the pick interval (m=10),
I	= average amplitude of the near-region pick interval.
The standard deviation, ST , of this set of 10 individual
In
amplitude segments (near region) shall be calculated accord-
ing to Equation AM1-4.
'in
m
I
i=l
(I.
- V2
(m-1)
(AM1-4)
The values of I,, R , R • ST SD , SD„ shall be calculated
T n T it Kn KT
using this same procedure [Equations AM1-3 and AM1-4].
The plume opacity, 0 , is calculated according to Equation
P
AM1-2. Opacity in percent is calculated by multiplying the
square root of the expression in the brackets of Equation
AMI-2 by 100.
The standard deviation, SQ, of each opacity value, Op, shall
be calculated. It is obtained by a multi-variable function
which is given in terms of the standard deviation o1 the

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27
individual variables. Given Equation AM1-2 for opacity and
the standard deviations previously calculated, the standard
deviation of the opacity value is calculated according to
Equation AM1-5.
where:
SQ = standard deviation of the opacity value, Op.
90p/aRn = partial derivative of the opacity function
[Equation AM1-2] with respect to the clear-air ref-
erence signal variable in the near-region [Figure AM1-6].
Spn = standard deviation of the pick-interval segments
for the clear-air reference signal in the near-region.
90p/9Rf = partial derivative of the opacity function
with respect to the clear-air reference signal vari-
able in the far-region.
= standard derivation of the pick-interval segments
for the clear-air reference signal in the far-region.
0Op/3In = partial derivative of the opacity function
with respect to the plume backscatter signal variable
in the near-region.
ST = standard deviation of the pick-interval segments
for the plume backscatter signal in the near-region.
30p/3I^ = partial derivative of the opacity function
with respect to the plume backscatter signal variable
in the far-region.
Sj^ = standard deviation of the pick-interval segments
for the plume backscatter signal in the far-region.
The calculated values of 0 , S , I , R , I,, R,, SD ,
p' o' n' n' f f Rn
Snj-, ST and S,c shall be recorded as a permanent record
Rf' In If	^
along with the time that the lidar recorded the plume
backscatter signal.
(AM1-5)

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28
2.4.2 Reduction Mechanism for Opacity Data. As given in Section
2.2. 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 charac-
teristics and variability of the source emissions. The
lidar data rate is nominally set at one opacity measurement
every 10 seconds throughout a given data run.
The mechanism by which the set of individual opacity values,
Op, comprising a given data run are reduced, is a function
¦v of the air quality regulation to be enforced. When a given
state air pollution 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 reduc-
tion of the opacity data. If the respective regulation spec-
ifies an 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 or data rate,
calculated for this interval shall be averaged yielding an
average opacity, Op, for this interval. If the average opac-
ity is greater than that permitted by the regulation, then
the source is in violation.
The average plume opacity, Op, for the I-minute time interval
shall be calculated as the average of the consecutive (in
time) individual 1idar-measured opacity values, Op, by using
Equation AM1-6. (The I-minute time interval is called the
"averaging interval").
1 1
0 = - Z 0 .
p l k=i ek
(AMl-6)

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29
where:
0	, = the kth opacity value in the (I-minute) averaging
" i nterval,
1	= the sum of the individual opacity values,
1 = number of individual opacity values contained in
the averaging interval,
Op = average opacity over the averaging interval.
If the respective regulation specifies an opacity limit for
an I-minute interval and the data run were J-minute;> in length
(J > I), then a running average or progressive average shall
be used to reduce the lidar opacity values for a given data
run. The mechanism for the running average is shown in Figure
AM1-7. The I-minute interval shall be maintained constant
in length (temporal) being moved along the entire length of
the J-minute data run. Once the opacity values, from 1 to i
[Figure AMl-7(a)] have been averaged for the first I-minute
time interval by Eq (AM1-6), the running average is performed
by successively subtracting the mth value and addinij the n +
1 value [Figure AMl-7(d)] and calculating the averaqe 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 consecutive 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 shall be the same throughout J. A few of the i values may
possibly be rejected due to the Opacity Data Acceptance/
Rejection Criterion presented in Section 2.4.3 of this method.

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1 2 3 4 ... 1
(a) First average opacity, Op, calculated for the i opacity values
1 2 3 4 . . . i i+1	j
(b) Second average opacity calculated, first opacity value subtracted and the
(i+1) value added.
12 3 4
—hH	r-
. l i+1 i+2
(c) Third average opacity calculated, second opacity value subtracted and the
(i+2) value added.
K-
i i i i-
1 2 3 ^
H	h
+
H	1—\-
i i+1 i+2	m-1 m m+1
n-1 n n+1 n+2
(d)	The mth average opacity calculated.
b—i	>4
i—i—i—i	1—i—i	1	1—i—i
1 2 3 14 ... i i+1 i+2	j-i ... j-2 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 AM1-7. Pictoral Diagram of the Running Average.

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31
When the applicable control regulation specifies a maximum
opacity value as a function of time, then the lidar opacity
values, measured on the nominal 10-second data rate, are
reduced accordingly by computer. The time intervals over
which the opacity values exceed the maximum given in the
control regulation shall be summed together within the speci-
fied consecutive or overall time period. If the summed time
period exceeds the allowable time period the source is in
violation. An example of this is the following: Suppose
the state regulation states that short-term occurrences shall
not exceed 50% opacity from a period aggregating 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 summod together.
If the sum of the intervals exceeds 5 minutes in any 60 con-
secutive minutes then the source is in violation. The same
holds true if the sum of the individual time intervals exceeds
20-minutes in any 24-hour period.
If there is no applicable state air pollution control reg-
ulation 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 AM1-7 I is
equal to 6 minutes and J is 6 minutes or longer.
The opacity of intermittent visible emission and cyclic proces-
ses is measured over a period of time considered adequate to
determine compliance/noncompliance with the applicable regu-
lation. A cyclic process is defined in Figure AM1-S.
0. = 0%
Figure AM1-8 Cyclic Process

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32
If the regulation, such as a state or city regulation in an
approved state implementation plan (SIP), specifies an opacity
limit as a function of time, the 1idar-measured opacity values
shall be added together in accordance with the requirements
of the regulation.
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 shall be 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 support of 40 CFR Part 51 with opacity limits as a function
of time, this method shall be employed by summing the respec-
tive opacity measurement time intervals for the required
period of time.
2.4.3 Opacity Data Acceptance/Rejection Criterion: The plume opacity,
Op, is calculated from the lidar backscatter signal data
using Equation AM1-2. The standard deviation, SQ, of each
respective opacity value is calculated using Equation AM1-5.
SQ is an indicator of the quality or integrity of the optical
backscatter signal segments from the near-region and the
far-region of the lidar 1ine-of-sight [Figure AM1-4], and is
termed an atmospheric noise indicator.

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33
In the course of reducing large amounts of 1idar-measured
opacity data, it was empirically or fundamentally determined
that if SQ is greater than 8% (calculated with the plume
opacity, 0 , for the selected near-region and far-region
P
pick intervals), the lidar backscatter signal is not reliable
(too noisy) for an accurate opacity measurement. In this
case the respective opacity value shall be discarded.
For a given data run, if the average of the respective indi-
vidual standard deviation values, SQ, of a set of opacity
values in an averaging interval, I, is greater than 8% (also
based on 100% opacity full scale) then the average opacity,
0p, for that interval shall be rejected and discarded from
whole data run. This average is calculated using Equation
AM1-7.
1
S = - Z S ,	(AM1-7)
0 1 k=l 0k
where:
S . = the kth standard deviation value of the data set I,
ok	'
I = the sum of the individual standard deviations,
1 = the number of individual standard deviation values in
a given data set,
SQ = the average standard deviation for a given data set.
2.4.4. Elevation/Azimuth Angle Correction Criterion. To ensure
true plume opacity for a given plume under-test, the effect
of the elevation angle (angle of inclination of the lidar
transmitter/receiver) of the lidar firing through a vertical
plume shall be taken into consideration in the opacity calcu-
lation. The elevation angle is measured with respect to the
horizontal reference line. As shown in Figure AM1-9, the
optical plume opacity is typically measured with the lidar

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Stack's Vertical Axis
Vertical Smoke Plume
Lidar Elevation or
Inclination Angle
Horizontal Plane
Effective Plume Thickness
Actual Plume Thickness
LCosB
Opacity measured along path L
Opacity value corrected to the
actual plume thickness, P
Lidar Line-of-Sight
Referenced to Level Ground
(Horizontal Plane)
Smoke Stack
Figure AMI - 9. Elevation Angle Compensation for Vertical Plumes.
CO

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35
along the inclined path L. The opacity value ultimately
required is along path P, the horizontal thickness of the
plume.
An individual 1idar-measured plume opacity value, Op, shall
be corrected for elevation angle if the lidar transmitter/
receiver elevation or inclination angle, pp, is greater than
or equal to the value calculated in Equation AM1-8.
(ip>Cos-1[l-M].Opin%,	(AMI-
If Pp is greater than or equal the expression on the right
side of Equation AM1-8 then the opacity value, Op measured
along the lidar path L shall be mathematically modified or
corrected to obtain the opacity value, 0pC, for the actual
plume (horizontal) path or thickness P, by using Equation
AM1-9.
0 = 0 Cos p	(AM1-9)
pc p Hp
This correction keeps the maximum difference of (0 - 0 )
p pc
to approximately 1% (full scale). A given 0pC shall be used
in place of its respective Op in the Reduction Mechanism
[Section 2.4.2].
When measuring the opacity in the residual region of an
attached stream plume [Section 2.2.1 of this Method], the
lidar shall be positioned in relation to the stack so that
the lidar 1ine-of-sight is nearly perpendicular to the
direction of the horizontal drift of the plume, to the ex-
tent practiable [Section 2.1 of the Method]. This proced-
ure will essentially keep the lidar 1ine-of-sight distance
through the plume equal to the actual plume thickness at
the point of opacity measurement. However, if the direc-
tion of drift of the plume should change so that the lidar

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36
1ine-of-sight does not pass through the plume nearly perpen-
dicular, then an azimuthal angle correction shall be made to
the calculated opacity values obtained under this condition.
The geometry of this correction is defined in Figure AM1-10.
This correction shall also apply to the other plume types if
the opacity measurement is made more than 3 source diameters
away from the source outlet. The drift angle, e, is obtained
from Equation AM1-10.
e = Cos
-l
R2 . R2
1 r
2 RjR
A
R2
2
(AMI-10)
where:
Rx = the lidar range to the position within the resid-
ual plume where opacity measurements are being performed,
Position 1 in Figure AMl-lO(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, Postion 2 in Figure AM1-
10(a).
R^ = the distance along the center line of the plume, in
the direction of drift, from Position 1 to Postion 2 [Figure
AMl-lO(a)].
Ri and R2 are measured directly from the respective plume
backscatter signals at the center of the plume spike. The
angle a is measured at the pedestal of the lidar transmitter/
receiver.

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Position of the Lidar
within residual plume
measurement [Position
1i ne-of-sight
for opacity
!]•
Plume Direction of Drift
perpendicular to the Lidar
1ine-of-sight at initial
setup of the Lidar (along
plume center line); e = tt/2.
Plume Direction of Drift
later in time, not perpendicular
to the Lidar 1ine-of-sight (along
plume center line).
Position within the plume selected in
order to measure the plume drift angle
[Position 2].
Lidar Position
(a)
Plume Dr
Lidar Line-of-Sight,
Position 1
(b)
Figure AMI-10. Correction in Opacity for Drift
Residual Region of an Attached Steam Plume.

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38
If e > 100° or e < 80° for Op in the range from 50% to 100%,
if e > 105° or £ < 75° for Op in the range from 20% to 40%,
and if e > 120° or e < 60° for Op in the range from 1% to
20%, then the azimuthal correction shall be performed on
the lidar measued plume opacity value 0 using Equation AM1-11.
P
0 = 0 Cos ( ~ - e) = 0 Sin £	(AM1-11)
pc p	2	p
where:
Op = the opacity value measured along the lidar path L',
which is the thickness of the plume along the lidar line-of-
sight through the plume, Position 1 in Figure AMl-10(b).
0pC = the actual plume opacity along the corrected path P'
[Figure AMl-10(b)]. A given 0 shall be used in place its
pc
respective 0 in the Reduction Mechanism [Section 2.4.2].
P
There may be testing situations where both the azimuth and
the elevation corrections 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.
2.4.5 Lidar Data Analysis Record. While the lidar data analysis
and reduction are being conducted permanent records shall
be initiated and maintained. In these records, which may be
a laboratory log book or the paper output from a computer
printer, the measured or calculated values for I , Sjn; 1^,
SIf; Rn' SRn' Rf' SRf' Rs' Pp' ^ R6i|i: Rl* Rz' a' e; °p'
S0, 0pC, along with the respective units (meters, nanoseconds,
etc), shall be recorded for each final opacity calculation.
It shall be clear, from these records, what data processing
operations were used to calculate the final opacity value

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39
from a given plume data signal. During the data reduction
process (Section 2.4.2 of this Method) the values of Op (which
was calculated from the applicable 0 and 0 values) and S
p pc	o
shall be documented along with the applicable parameters
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 measurement
shall also be recorded for each final opacity calculation.
The identity of each criterion used in the data analysis
and the identity of any opacity values rejected [Section
2.4.3 of this Method] shall be recorded for each applicable
opacity value.
3. Lidar calibration and operational error. The lidar shall be
calibrated in the field to ensure the accuracy of the opacity
data as measured. The calibration also verifies the opera-
tional integrity of the optical receiver and the analog/digi-
tal electronics.
3.1. Calibration requirements. In
there are six parameters that
This is accomplished by means
the calibration of the lidar
shall be directly verified,
of two techniques.
Technique 1 - Use of neutral density optical filters to
simulate opacity with a He~Ne laser or a light-emitting diode
as the optical (red light for a lidar containing a ruby laser)
source. The narrow band filter (6943 Angstroms peak) shall
be removed [Section 4 of this Method] from its position in
front of the photo-multiplier (PMT) detector. Neutral density
filters of nominal opacities of 0, 20, 40, 60 and 80% shall
be used. The recommended test configuration is depicted in
Figure AM1-11.

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PMT Entrance
Window Completely
Covered

U
Lidar Receiver
Photomultipller
Detector
(a) Zero-Signal Level Test
He-Ne Laser or
Light-Emitting Diode
(Light Source)
light path
Lidar Receiver
Photomultiplier
Detector
(b) Clear-Air or 0% Opacity Test
Neutral-density
optical filter
/
He-Ne Laser or
Light-Emitting Diode
(Light Source)
light path
Lidar Receiver
Photomultipl ier
Detector
(c) Optical Filter Test (simulated opacity values)
*Tests shall be performed with no ambient or stray light reaching the
detector.
Figure AMI-11. Recommended Test
Configuration for Technique 1.

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41
Technique 2 - Use of an optical generator (built-in calibra-
tion mechanism) that contains a highly-controlled light-emit-
ting-diode (red light for a lidar containing a ruby laser)
which, by injecting an optical signal into the lidar receiver
immediately ahead of the PMT detector, simulates an actual
lidar return from a given atmospheric path through a plume
or in clear air. The optical generator shall simulate opti-
cal signals representing clear air or 0% opacity, 20, 40, 60
and 80% opacities (nominal). An optional 10% simulated
optical signal may also be included.
The six parameters are the following:
1.	The zero-signal level (receiver signal with no optical
signal from the source present) shall be verified for
proper digitizer adjustment or video offset on the oper-
ator's oscilloscope display, and there shall be no spur-
ious noise in this signal.
2.	The opacity value of 0% shall be verified from the light
source through the PMT detector, data processing elec-
tronics and as calculated by computer.
3.	A minimum of 4 opacity (>0%) values shall also be veri-
fied through the lidar detector, data processing elec-
tronics and as calculated by computer.
The neutral density filters and the optical generator shall
be calibrated for actual opacity once per month while in use.
The calibrated opacity value of each filter or each optical
generator simulated opacity value shall be recorded in the
lidar log book [Figure AM1-3]. The filters shall be calibrated
within a laboratory accuracy of + 2% or better. The optical
generator shall be calibrated with an accuracy of + 1% or
better.

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42
The calibration of the lidar is conducted for each of the
two video signal channels (linear and logarithmic [if so
equipped] channels) as they are used for data collection.
The calibration shall be performed for each emissions source
tested. For one given source-under-test the calibration
shall be performed once (minimum) every 4-hour period.
3.2. Calibration procedures. With the entire lidar receiver and
analog/digital electronics turned on and adjusted for normal
operating performance, the following procedure shall be used
for Technique 1.
3.2.1 Procedure for Technique 1. This test shall be performed
with no ambient or stray light reaching the PMT detector.
The zero-signal level shall be measured and recorded (on
magnetic tape) as indicated in Figure AMl-ll(a). The simu-
lated clear-air or 0% opacity value shall be tested by using
the selected light source depicted in Figure AMl-ll(b). (A
laser beam may have to be optically attenuated so as not to
saturate the PMT detector). This signal level shall be mea-
sured and recorded on magnetic tape. The opacity value is
calculated by taking 2 100-nanosecond pick intervals about 1
microsecond apart in time, and using Equation AM1-2 setting
the ratio R /R, = 1. This calculated value shall be recorded
n f
in the lidar log book.
The simulated clear-air signal level is also employed in the
optical test using the neutral density filters. Using the
test configuration in Figure AMl-ll(c), each neutral density
filter is separately placed into the light path from the
light source to the PMT detector. The signal level is mea-
sured and recorded manetic tape. The opacity value for each
filter is calculated by taking the signal level for that
respective filter (If), dividing it by the 0% opacity signal
level (In) and performing the remainder of the calculation

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43
by Equation AM1-2 with Rn/Rf = 1. The calculated opacity
value for each filter shall be recorded in the lidar log
book. The file address for each filter-signal recorded on
magnetic tape shall be recorded in the lidar log book.
3.2.2 Procedure for Technique 2. With the entire lidar receiver
and analog/digital electronics turned on and adjusted for
normal operating performance, the optical generator is turned
on and the signal, uncorrected for 1/R2, selected with no
plume spike signal or opacity value selected. This is a
simulated clear-air atmospheric return signal is displayed
on the system's oscilloscope display. The lidar operator
then makes any fine adjustments that may be necessary which
may include detector high voltage and input/offset values on
the digitizer (analog-to-digital signal converter). This
signal is then switched to the 1/R2 corrected signal.
With the digital tape recorder turned on, the magnetic data
tape properly marked and installed, and the computer program/
selectable parameter values read into the computer memory
via magnetic tape or keyboard, the system is ready for the
calibration verification test. Either the linear or the
logarithmic video channel is selected that will be used to
measured stationary source emissions. (The linear channel
is used to measure plume opacity values less than 50 to 60%
while the logarithimic channel (optional) is used for opacity
values greater than 50% and where large video signal dynamic
range is required such as in an urban area where pollutant
loading in the local atmosphere is quite high.) If both
channels are expected to be used, then both shall be checked
for calibration.
The opacity values for 0% and the other four or five values
are selected one at a time in any order. The computer receives
the simulated return signal data, records each signal on
magnetic tape and calculates the respective opacity value

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44
(this measurement/calculation shall be performed at least 3
times for each selected opacity value). Each of the opacity
values from the optical generator shall be verified, while
the order is not important, for the respective video channel
to be used.
The calibrated optical generator opacity value for each selec-
tion is recorded in the lidar logbook in the Lidar Function
Verification Section [Figure AM1-3]. The average of the
three opacity values calculated by the computer for each
selection is also recorded in the logbook. The file location
or address on the magnetic data tape for each respective
simulated video signal is also recorded in the logbook.
3.3. Calibration error. If after the calibration procedure has
been completed the lidar measured opacity value is not within
+3% (full scale) of the actual calibration value (opacity
value of the neutral density filters or the optical gener-
ator) as follows:
Linear Channel	- + 3% over the opacity range of 0%
through 60%
Logarithmic Channel - + 3% over the opacity range of 20%
(Optional)	through 80%
then the lidar shall be considered out of calibration. Remed-
ial action shall be taken to correct any equipment or computer
problems that may be present. The calibration test shall
be performed again. This process shall be repeated until
the above conditions are fulfilled.
4. Specification for Basic Lidar Apparatus. The performance/
design specification for a basic lidar system is provided in
this section. This specification is directly addressed to a
lidar system using a ruby laser as the optical transmitter.

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45
The essential components of a basic lidar system are depicted
in Figure AM1-12, the functional block diagram. The types
of components given and identified for this system have been
proven in the EPA Omega-1 Lidar. Other components may cer-
tainly be used in fabricating a lidar system if they meet or
exceed the relevant performance characteristics of the compo-
nents identified in this section. The components of the
lidar instrumentation are identified as follows:
a) Q-switched ruby laser - The laser shall have a minimum
output energy of 1 joule per pulse with a pulse duration
(length) of less than 35 nanoseconds (full width, half
power). It shall be capable of being fired at a sustained
rate of 1 pulse every 10 seconds (6 pulses/minute).
The beam divergence (beam spread with range) angle shall
be 1.5 milliradians (full angle, half energy) maximum,
which may necessitate the use of an up-col1imating tele-
scope on the front of the laser. Inherent laser beam
divergence is a function of the ruby rod quality, the
higher the quality the smaller the divergence angle.
-	Holobeam Series 300 and 600 laser, equivalent perfor-
mance or better meeting the specifications given above.
(b)	Reflective Telescope - The telescope shall be a cassegrain
reflective instrument with a minimum primary mirror
diameter of 20 cm (8 in). A standard amateur astronom-
ical telescope performs efficiently at the ruby (red
light) wavelength.
-	Celestron 8 inch reflective telescope, equivalent
performance or better.
(c)	Aiming Telescope - This device is a standard rifle scope
with an optical power or magnification of 10 or 12.

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Mam Power Supply
Transmitted Light Pulse
Q-Switch Power Supply
Sw itched
W ater Coo ler
Ruby Laser
Laser Controls
Backscatter Return Signal
Reflective Telescope
PMT
Detector
Logarithm ic
(C ass eg rain)
(b)
Logarithmic Video Signal
iming Telescope
F ast Trans lent
Recorder or Digitizer
PMT Detector
H igh Voltage
Interface Bus
Power Supply
Digital Computer
D ig it a 11 /R 2 Correction
Opacity Calculation
(Variable) (d)
(I)
Interface Bu
Pr inter
M agnetic Tape
(paper output)
Figure AM1-12 Functional Block Diagram of a Basic Lidar System
4*
<7>

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47
(d)	PMT Detector Power Supply - This is a standard PMT high-
voltage power supply variable over the range from 1.0
to about 3.0 KVDC.
(e)	Photomultiplier Detector - The PMT used in the EPA Omega-1
Lidar is of special design to eliminate the problems of
afterpulsing or signal induced noise encountered in
standard off-the-shelf detectors. This detector has 8
dynodes and a gain of 10s at less than 2.5 KVDC. It
has a low impedance photo cathode. The measured quantum
efficiency is approximately 5% of the ruby wavelength
of 6943 Angstroms. Its spectral response approximates
S-20.
-	ITT PMT Detector No. 4084 fabricated to EPA specifi-
cations, equivalent performance or better.
(f)	Narrow Band Optical Filter - This filter keeps all opti-
cal radiation that enters the receiver from reaching
the PMT detector with the exception of the extremely
narrow band which contains the ruby wavelength. Its
center wavelength is 6943+2, -0 Angstroms at 75°F.
Its half height bandwidth is less than 14 Angstroms.
The peak optical transmittance of this two-cavity, type
2 filter is approximately 51%.
-	Dell Optics Co. Laser Optical Interference Filter
Part Number H-10, equivalent performance or better.
(g)	Logarithmic Channel Amplifier - This amplifier basically
deamplifies strong return signals, gain <1, while it
greatly amplifies weak return signals, gain >> 1. Its
bandwidth is 30 MHz with a rise time of 11.7 nanoseconds.
Its linearity is less than + 1.0 dB. Its slope is nomin-
ally 25 millivolts/dB with an overall gain of 100 dB.

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48
-	Aertech Industries Logarithmic Video Amplifier Model
LDN-1000-1, equivalent performance or better.
(h)	Fast Transient Recorder (Digitizer) - This instrument
converts the analog backscatter (or logarithmic video)
signal to a computer-compatible digital form. The out-
puts are to the computer and the oscilloscope display
which is continuous due to refresh memory.
-	Biomation 8100 Waveform Recorder, equivalent perfor-
mance or better.
(i)	Digital Computer - The computer carries out the required
data handling, equipment address assignments and data
transfer to the magnetic tape recorder in addition to
performing the plume opacity and other calculations.
-	Hewlett Packard 9825A Programmable Calculator, Digital
Equipment Corp. PDP-11-03 or Data General Nova 3 compu-
ters, equivalent performance or better.
(j) Magnetic Tape Drive/Formatter - This compound instrument
records and plays back the lidar backscatter signal
data. It can be 800 or 1600 bits per inch with a nominal
read/ write speed of 25 inches-per-second. Tape format
shall be industry compatible.
-	Kennedy Tape Drive Model 9800 interfaced to a Dylon
Corp. 1015 A Formatter, equivalent performance or better.
(k) Oscilloscope Display - The scope provides a continual
monitor of the lidar backscatter signals for the lidar
operator.
-	Tektronix Model 475 oscilloscope, equivalent or better.

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49
(1) Digital Clock - The digital clock provides time
to the nearest second to the computer for each
lidar backscatter signal. The time on the clock
is set either manually or by the computer.
- Hewlett Packard Digital Clock Model 59309A,
equivalent performance or better.
(m) Printer - Any standard line printer can be used
which can be directly interfaced to the computer
chosen. In the case of the Hewlett Packard 9825A
a thermal printer is an integral part of the
machine and another printer is not required.
As depicted in Figure AMI-12, the laser and the telescope are mounted
biaxially on a steerable mount or pedestal along with the PMT detector
and aiming telescope. The minimum convergence distance between the
laser beam and the telescope's instantaneous field-of-view shall be
50 meters.
Extra care must be taken not to route the video signal cables (coaxial
cable 5On impedence) adjacent to power, high voltage and remote control
wiring to eliminate electromagnetic interference. The AC power for
the electronics must be regulated and isolated from the 220VAC power
lines used for the laser. The list of references in Reference 5.1 in
addition to the text of this reference provides much information on
the theory, design fabrication and use of ruby lidars.
Each lidar system whether it employs a ruby laser or another laser as
the optical transmitter, must be subjected to performance and evaluation
tests, and properly qualified in order to be used under this method.
Several tests of this type are described in Reference 5.1.
The computer software necessary to fulfill the requirements of this
method can be readily developed from the contents of Section 2 of this
Method.

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50
5. References
5.1	The Use of Lidar for Emissions Source Opacity Determination,
U.S. Environmental Protection Agency, National Enforcement
Investigations Center, Denver, CO, EPA-330/ 1-79-003, Arthur
W. Dybdahl, current edition.
5.2	Field Evaluation of Mobile Lidar for the Measurement of Smoke
Plume Opacity, U.S. Environmental Protection Agency, National
Enforcement Investigations Center, Denver, CO, EPA/NEIC-TS-128,
February 1976.
5.3	Remote Measurement of Smoke Plume Transmittance Using Lidar,
C. S. Cook, G. W. Bethke, W. D. Conner (EPA/RTP). Applied
Optics 11, pg 1742, August 1972.
5.4	Lidar Studies of Stack Plumes in Rural and Urban Environ-
ments, EPA-650/4-73-002, October 1973.
Laser Safety References:
5.5	American National Standard for the Safe Use of Lasers ANSI Z
136.1-176, 8 March 1976.
5.6	U.S. Army Technical Manual TB MED 279, Control of Hazards to
Health from Laser Radiation, February 1969.
5.7	Laser Institute of America Laser Safety Manual, 4th Edition
5.8	U.S. Department of Health, Education and Welfare, Regula-
tions for the Administration and Enforcement of the Radiation
Control for Health and Safety Act of 1968, January 1976.
5.9	Laser Safety Handbook, Aiex Mallow, Leon Chabot, Van Nostrand
Reinhold Co., 1978.

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