oEPA
United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
EPA-600 '2-79-1 97
November 1 979
Research and Development
Mobil Lidar
System
Developments and
Operating
Procedures
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-79-197
November 1979
MOBILE LIDAR SYSTEM DEVELOPMENTS AND
OPERATING PROCEDURES
by
George W. Bethke
General Electric Company
King of Prussia, PA 19406
Contract 68-02-2979
Project Officer
William D. Conner
Emission Measurement and Characterization Division
Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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ABSTRACT
A smoke plume opacity-measuring mobile lidar system was refurbished,
modified, and tested on semi-transparent screen targets. This refurbishment
has involved retrofitting a new laser to a previously existing lidar
transmitter/receiver, designing and fitting a new laser monitor to the laser,
modifying and rebuilding the range correcting signal processor to be compati-
ble with the other mostly new lidar components, installing all the lidar
components into a new and larger van, and finally getting the entire system
to function together and become operational. The resultant lidar system
automatically analyzes, presents, and records smoke plume data, resulting
in a much faster data rate and easier analysis than was formerly possible
with the earlier versions of this lidar system. Complete operating procedures
for the improved system are presented.
This report was submitted in fulfillment of Contract 68-02-2979 by
General Electric Company under sponsorship of the U.S. Environmental Protec-
tion Agency. This report covers a period from September 1978 to June 1979,
and was completed as of June 1979.
in
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CONTENTS
Abstract ill
Figures vi
Tables vi
1. Introduction and Scope 1
2. Lidar System Description 2
Optical/mechanical system 2
Electronic system 8
3. Operating Instructions 12
Turn-on procedure for van 12
Laser operation 12
Lidar operation 14
Plume data analysis 20
4. Special Instructions and Precautions 22
Motor generator usage 22
Laser precautions 22
Laser special purpose instructions 24
Lidar signal and linearity limits 25
Lidar receiver-transmitter alignment 27
5. Laser Monitor 29
6. Lidar Signal Processor 31
7- Screen Target Tests 38
References 42
v
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FIGURES
Number Page
1 Mobile lidar system van 3
2 Lidar in storage/travel position 4
3 Optical block diagram of the lidar transmitter/receiver 5
4 Electronic block diagram for the lidar system 9
5 Lidar electronics ready for normal operation 10
6 Oscillograms showing form of typical lidar signals 18
7 Laser monitor and monitor bias circuit 30
8 Lidar signal processor (LSP) front and rear panels 32
9 LSP circuit diagram for board receptacles and end panels 33
10 LSP circuit diagram for card 3 34
11 LSP circuit diagram for card 2 35
12 LSP circuit diagram for card 1 36
TABLES
Number Page
1 Lidar Transmitter Characteristics 6
2 Lidar Receiver Characteristics 7
3 Lidar Data Handling System Cable Connections 11
4 Initial Front Panel Settings for Electronics 15
5 Detector Space Charge-Limited Linearity 26
6 Transmittances from Lidar Data Processor (LDP) Data 40
7 Comparison of Oscillogram with LDP Transmittances 41
vi
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SECTION 1
INTRODUCTION AND SCOPE
The purpose of this program has been to complete the refurbishment and
modification of the EPA/RTP smoke plume opacity-measuring mobile lidar
system, as well as test the system on semitransparent screen targets. The
resultant lidar system automatically analyzes, presents, and records smoke
plume data, resulting in a much faster data rate and easier analysis than was
formerly possible with the earlier versions of this lidar system[l-3].
As refurbished, the previously existing and still-used GFE components
from the old lidar system[l-3] include the laser water cooler, the lidar
pedestal, and the lidar receiver including the special grid-gated
photomultiplier tube (PMT) detector and the PMT power supply. The newly-
incorporated GFE components include a Tektronix R7704 oscilloscope (with two
7A15A amplifiers plus one 7B50 time base), a Biomation 8100 transient
recorder (TR), an SRI lidar data processor (LDP), a Hewlett Packard 5055A
printer, an H.P. 8013B pulse generator, a Holobeam 321 pulsed ruby laser, and
a CMC Transmode van equipped with two 6.5 kW motor generators.
The scope of this lidar refurbishment effort is briefly summarized
below:
1) Laser retrofit: Made the new laser operational, integrated the water
cooler into the laser operation, designed and fabricated the laser cover, and
mounted and aligned the laser on the lidar transmitter-
2) Laser energy monitor/trigger development: Designed, constructed,
tested, and calibrated a new laser monitor which is compatible with the lidar
data processor (LDP).
3) Lidar signal processor (LSP) development: Modified and re-built the
range-correcting time-squared amplifier to make it compatible with a new ramp
source and a low input impedance transient recorder.
4) Mechanical/electrical installation: Installed all lidar components
into the van, and interconnected them as necessary.
5) System integration and operation: Optically aligned the entire
system, re-adjusted the van motor generators to permit lidar operation, and
made the entire lidar system operational.
6) Screen target tests: Conducted lidar outdoor tests on a series of
screen targets with different densities, and analyzed the results so as to
establish the best usage of the LDP outputs.
1
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SECTION 2
LIDAR SYSTEM DESCRIPTION
The lidar system is mounted in the rear half of the QIC Transmode van,
which includes two inboard 6.5 kilowatt motor generators (MG). A sliding roof
opening over the lidar transmitter/receiver and its elevating pedestal allows
the lidar to be oriented as necessary to interrogate smoke plumes. Figure 1
shows the van with lidar elevated and protuding from the roof. During travel,
the lidar is lowered and is additionally bolted to a cross-brace as shown in
Figure 2. One of the MG sets is used to power the laser and water cooler,
while the other MG Bowers all other components.
OPTICAL/MECHANICAL SYSTEMS
The lidar transmitter and receiver are both bolted to a common base
plate, with the receiver being adjustable in pointing direction[2] so as to
allow proper alignment with respect to the transmitter output beam. Figure 3
shows an optical block diagram of the transmitter/receiver optics, as well as
indicating the physical layout.
Referring to Figure 3, the lidar transmitter consists of a Holobeam 321
pulsed ruby laser which is beamed through negative lens LI and air-spaced
a chroma t objective lens L2. The combination of lenses LI and L2 form a
Galilean-type 9-power up-collima ting telescope which increases laser beam
diameter and decreases its divergence as shown in Table 1. The laser energy
monitor/lidar trigger consists of a silicon photodiode which views (through
appropriate filters) the laser light scattered from the laser output window
material. This photodiode is located in the laser output window support
structure. Table 1 lists more lidar transmitter and laser details.
Again referring to Figure 3, the back-scattered light is collected by a
6-inch diameter objactive lens L3, focussed on field stop FS, and collimated
by lens L4. The resultant collimated beam then passes through narrow band
interference filter IF which is located in a thermally controlled cell with
windows Wl and W2. Finally, the filtered beam is moderately scattered by
ground glass GG before falling on the photomultiplier tube (PMT) detector.
References 2 and 3 give full details about the receiver and mount, but for
convenience many characteristics are summarized in Table 2.
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Figure 1. Mobile lidar system van, with van roof open and
lidar transmitter-receiver in operating position.
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Figure 2. Lidar in storage/travel position, and van roof closed.
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Thermally
Controlled
Filter Cell
TininRPAM ^91
—
LI
RUBY LASER
u
SL1
nL
JI2
/
*~
I
L2
COVER
Figure 3. Optical block diagram of the lidar transmitter/receiver.
Dimensional relationships are approximately correct.
Transmitter/receiver center-line separation is 8 inches,
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TABLE 1. LIDAR TRANSMITTER CHARACTERISTICS
Laser
Manufacturer and model
Type
Output wavelength
Output energy
Pulse width (FWHH)
Beam divergence
Beam diameter
Ruby rod size
Repetition rate
Cooling
Laser power requirement
charging current
"Idle" current
Pockels cell requirement
Laser Collimation
Upcollimator power
Upcollimator objective
Collimated beam diameter
Collimated beam divergence
Monitor/Trigger
Detector
Location on laser
Holobeam Model 321
Pockels cell Q-switched ruby
6943A1 *
*
2 joules/pulse maximum
/ *
20 nsec at 2 J/pulse
2.5 mrad (full angle, % power)
0.85 cm
*
0.95 cm diam. x 7.6 cm long
0-15 ppm
Deionized water
210-230 VAC, 60 Hz, 1 phase
20 amps (for 1 sec)
1 amp
115 VAC, 60 Hz nom.
9X
12.7 cm (5") diam., f/5 air spaced
7.6 cm (3")
<0.5 mrad (full angle, % power)
Silicon photodiode (PIN-3D)
Output window assembly
Information supplied by laser manufacturer.
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TABLE 2. LIDAR RECEIVER CHARACTERISTICS
Aiming Optics
Type
Riflescope power
Receiving Optics
Type
Objective lens
Collimating lens
Field of view
Interference Filter
Manufacturer
Type
Diameter
Transmission peak wavelength
Transmission center wavelength
Thermal shift
Bandwidth (FWHH)
Peak transmittance
Residual transmittance
Filter rejection
Filter tilt in lidar
Photomultiplier Tube Detector
Tube manufacturer and type
Number of dynodes and type
Photocathode characteristics:
Sensitivity type
Quantum efficiency
Quantum efficiency
Tube response time
Grid gated on/off ratio
Grid AV for on ->• off
Riflescope
4X to 12X variable
Refracting
15.2 cm (6") diameter, f/5
5.4 cm focal length
4.0 mrad full angle
Infrared Industries
3 cavity interference
5.1 cm (2")
6946. 0& (25°C)
6943. 4^ (25°C)
+0.2 X/°C
12. OX
0.66
Far uv to >1.0 micron
0 (perpendicular to radiation)
IT&T F4084
8 linear focused dynodes
MA-2 (modified S-20)
4.8% at 6940A1
21% at 4080A1
<5 nsec
43 dB
-2.5 volts
This information is summarized from references 2 and 3.
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ELECTRONIC SYSTEMS
The lidar electronics consist of two separate systems, the laser system
and the lidar data handling system. Figure 4 shows a functional block diagram
which includes both systems, while Figure 5 is a photograph of the
electronics shelf. See the Holobeam laser manual for a discussion of the
laser system wiring and operating logic.
The lidar data handling system functions as follows: When the laser is
fired, a positive pulse from the laser monitor triggers the LDP which
displays a measure of the pulse height ("energy"), and also immediately
produces a trigger pulse for both the transient recorder (TR) and for the
oscilloscope time-base unit (used independent of the rest of the
oscilloscope). The time base sawtooth output provides a ramp for the LSP
range-corrector, while the time-base gate output is used to trigger the pulse
generator. After a selectable delay, the pulse generator produces both a
negative pulse for gating off the PMT during the intense smoke plume signal
and a positive palse for a non-shot check (if desired) on gate delay. Once
the lidar or test data is captured by the TR, then the LDP interacts [4] with
the TR, the oscilloscope, and the printer so as to provide a repeated
oscilloscope display of TR memory and also both an LDP display plus printer
recording of laser energy, shot number, the averages of each of two
selectable signal intervals (A and B) , the value of (B/A)^'2, and [1 -
Table 3 lists the lidar data handling system cable connections, and the
types of cables (mostly coaxial) needed.
Since additions were made to the laser interlock system, they are
described here and indicated in Figures 3 and 4. The laser manufacturer has
interlock switches located at the laser main power supply door and side
panels. The interlock line has since been extended to include a water
pressure sensing switch at the laser cooler (switch set for 10 psi, where
circulating water pressure is 20 psi), a laser cover switch at the top front
of the transmitter cover (II of Figure 3), and a lidar transmitter lens tube
switch (12 of Figure 3). Also, a shutter light (SL2 of Figure 3) has been
added to the outside of the lidar structure. SL2 is in parallel with the
laser manufacturer-supplied shutter light (SL1 of Figure 3) which is located
on the laser and thus under the laser cover.
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HV
Pockels
Cell PS
Ruby Laser
HV
Laser
PS
synch.
Pockels Cell
Remote Control
J3
PC trig out
laser
covers
water
to shutter
Laser
Monitor
Gated
PMT
Detector
-pulse
raw
signal
-HV
PMT
PS
Laser
Cooler
inter-
lock
J2 J3
Laser
Remote
Control
J4
J5
remote INHIBIT
remote FIRE
Pulse Gen.
+pulse
Lidar Signal
Processor(LSP)
Monitor PS
& pulse out
Range-
Correcting
Amplifier
Oscilloscope
~~ | (used in
Time Base | X-Y mode)
(not used |
for scope) t
+pulse
trig.
+ramp
+pulse
I
processed signal
data &
control
I I
I I
Lidar Data
Processor(LDP)
trig.
test
sig.
clock
data &
.control
chan A+
chan B+
Transient
Recorder
(TR)
chan B-
Figure 4. Electronic block diagram for the lidar system.
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Figure 5. Lidar electronics ready for normal operation.
The laser cooler is in the right background, while
the laser power supply is not in this view.
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TABLE 3. LIDAR DATA HANDLING SYSTEM CABLE CONNECTIONS
Type Cable
From
To
RG 62 laser monitor
RG 59 PMT-power supply (R)
RG 58 PMT "pulse input"
RG 62 PMT "output"
RG 58 pulse gen. "output(+)"
RG 62 LSP-M "sig. out"
RG 58 LSP-C "sig. out"t
RG 62 scope "+ sawtooth output" (R)
RG 58 scope "+ gate output" (R)
RG 58 LDP "monitor trigger out"
RG 58 scope "ext trig in"
RG 58 LDP "test signal out"
RG 58 LDP "display X out"
RG 58 LDP "display Y out"
RG 58 TR "clock out" (R)
RG 58 TR "X out" (R)
RG 58 TR "Y out" (R)
RG 58 TR "Z out" (R)
gray TR multipin connector (R)
gray LDP "HP 5055A printer" (R)
RG 58 LDP "Z axis display" (R)t
LSP-M "laser in"
PMT "HV input"
pulse gen. "output(-)"
LSP-C "PMT in"
TR "chan B, + input"
LDP "monitor in"
TR "chan B, - input"
LSP "ramp in" (R)
pulse gen. "tigger input"
scope "ext trig in"
TR "trigger 5VFS-50fi"
TR "chan A, + input"
scope "A horiz. input"
scope "left vert, input"
LDP "clock 8100" (R)
LDP "X axis 8100" (R)
LDP "Y axis 8100" (R)
LDP "Z axis 8100" (R)
LDP "Biomation 8100" (R)
printer multipin connector (R)
scope "high sensitivity Z axis
input" (R). Add 50 ohm load.
*key to abbreviations:
(R) = connector at rear
PMT = photomultiplier tube housing
LSP-C = lidar signal processor range corrector
LSP-M = lidar signal processor laser monitor
LDP = lidar data processor
TR = transient recorder
scope = oscilloscope
tMust be terminated with a 50 ohm load.
11
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SECTION 3
OPERATING INSTRUCTIONS
TURN-ON PROCEDURE FOR VAN
a) Make sure the laser power supply (PS) wall breakers are off, and all
equipment is off. If in doubt, turn off all wall breakers.
b) Connect each motor generator (MG) to the desired van power
distribution system (see Section 4).
c) Start motor generators. They should start after 5-15 seconds of
cranking. Before applying any loads, allow them to run at least until they
run smoothly (1 minute minimum).
d) Turn on all wall breakers except for those to the laser PS.
e) Turn on laser Pockels cell, transient recorder (TR), oscilloscope
(scope), lidar data processor (LDP), and lidar signal processor (LSP). Allow
at least one minute warm up, especially for the Pockels cell.
f) Turn on laser cooler water pump motor (switch is on side of cooler).
g) Turn on laser cooler thermal control system (lower switch on the
front of cooler), and set for water temperature not under 20°C.
h) As described in the LDP manual[4], check out the LDP/TR/oscilloscope
settings and operation using the LDP "TEST" signal.
i) After five minutes, check laser line voltage, and if necessary,
adjust voltage to the laser PS to 210-230 volts.
j) Turn on the wall circuit breakers to the laser PS.
LASER OPERATION
For these laser operational tests, first be sure transmitter objective
lens cover is in place.
Laser Turn-On Procedure
a) Turn on laser main PS via its remote control station power switch.
Note that the power switch light is always on if the laser wall plug is
powered.
12
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b) Turn shutter switch to ON and allow 5 seconds for shutter to open.
As soon as the shutter switch is turned on, the laser may he fired even if
the shutter is still closed.
c) When the laser is ready to fire, the interlock light (next to
shutter switch) is out and the DISCHARGED switch is illuminated.
d) If the interlock light is still on, the interlock circuit is open
somewhere and the laser will not operate. See Section 4 for interlock
locations.
e) Occasionally check laser line voltage to laser PS, and if necessary
adjust to 210-230 VAC.
Single Shot Operation of Laser
a) Set the Pockels cell delay control at 0.65 msec ("065") and voltage
at 10 kV.
b) When firing the laser, determine laser pulse energy from ENERGY
display on the LDP (see LDP energy calibration sheet). Alternately, determine
the laser pulse energy with the special integrating load as described in
Section 4.
c) Note that a remote control hand-held switch is available which
allows either remote firing (FIRE) or remote inhibiting (INHIBIT) of the
laser output.
d) Determine the PS voltage for approximate lasing threshold: Start the
search at about 4.5 kV bank voltage ("450" on digital dial), increasing (or
decreasing) by 0.05 kV ("005") each try. If threshold is not found, do not
exceed 5.0 kV during the search (see Section 4).
e) The laser will immediately charge and fire in about 1 sec when
CHARGED button is pressed (assumes J2 and J3 on the back of the remote
station are still connected together as delivered).
f) See Holobeam data sheets and Section 4 for approximate output vs.
bank voltage above threshold. Approximately 300-500V above threshold (about
0.6-1.0 joule/single pulse) is recommended for most uses. If large outputs
are desired, start at low outputs and work up.
g) As detailed in the Holobeam manual and in Section 4 of this manual,
use special care at >5.0 kV (or >500V above threshold) to avoid overdriving
laser.
Automatic Firing of Laser
a) Follow above single shot procedure to establish threshold and
approximate desired output.
13
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b) Then press AUTO and adjust the pulse rate selector dial for any
value up to 15 ppm. See manual for extra precautions for use at relatively
high pulse rates.
c) Note that when AUTO is pressed, the first shot occurs at the end of
the pre-set firing interval.
d) AUTO cycle firing is terminated by pressing DISCHARGED button.
Turning Off Laser System
In order:
a) Turn off laser components.
b) Turn off wall circuit breakers for laser PS.
c) Turn off cooler.
d) Turn off generators.
LIDAR OPERATION
During all lidar laser shots, one system operator must be responsible
for aiming the lidar and monitoring the target area through the aiming
riflescope. This "safety/aiming" operator can fire the laser with the hand-
held remote control switch attached to the FIRE remote connector, or can
prevent laser firing with the remote control switch attached to the INHIBIT
remote connector.
a) Establish laser operating conditions as described above.
b) For initial lidar operation, pre-set all non-laser electronics front
panels as shown in Table 4. The scope display resulting from this set of
control settings is 1 microsec/cm horizontal (150 meters of lidar range/cm of
scope sweep).
c) Turn on all remaining items, except leave the pulse generator turned
off.
Initial Lidar Shots
a) Remove lens covers from both transmitter and receiver.
b) Open van roof cover, loosen lidar from travel brace, and elevate/aim
lidar at clear sky near plume of interest.
c) Set laser for desired operating condition (see above).
14
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TABLE 4. INITIAL FRONT PANEL SETTINGS FOR ELECTRONICS
Biomation 8100 Transient Recorder (TR)
Set all push switches out except where noted otherwise:
Channel
coupling
+_ input range
input offset
input/off
Arm
Delay =0.00
Level = +00
Mode = AUTO (in)
chan A
+ input DC (in)
0.2V
-0.99
OFF (in)
Trigger
Delay =0.00
Level = +0.20
chan B
- input AC (in)
1.0V
-0.99
INPUT (in)
Time Base: Sample interval = 0.01 ysec
Output; AUTO (in)
Display: XI (in)
Tektronix R7704 Oscilloscope (scope)
Set all push switches out (and light off) except where noted
otherwise:
Vert. Mode = LEFT (in)
Horiz. Mode = A (in)
7A15A Amplifiers: Vert, (left) ampl. Horiz. (right) ampl.
polarity = + UP
mag = XI
coupling = DC
volts/div. = 0.1 volt
7B50 Time Base:
+ UP
XI
DC
50 mV
display mode = TIME BASE (in)
time/div =0.5 ysec/div.
level/slope knob = ^10:30
SRI Lidar Data Processor (LDP)
Processor controls = AUTO, ALL, INHIBIT
Cursor Width: A = 050, B = 100
Hewlett Packard HP-5055A Printer
Operate/Standby = OPERATE
mode = NORM (in)
coupling = AC (in)
source = EXT (in)
(continued)
15
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TABLE 4. (continued)
GE Lidar Signal Processor (LSP)
Range corrector: gain = 5X, flatness =5.0, switch = DIRECT
Power Designs 3K10 Power Supply
Set voltage to 1500 volts
HP 8013B Pulse Generator
pulse period switch = extreme left
pulse delay switch = extreme left, vernier = full ccw
pulse width switch = extreme left, vernier = full cw
Output Controls;
-output +output
amplitude switch max up max down
amplitude vernier full cw full ccw
offset OFF OFF
mode - NORM
internal load - IN -
16
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d) Fire laser, either from console or remotely by safety/aiming
operator. (Target area must be monitored by safety/aiming operator.)
Resulting oscilloscope display should be like Figure 6a except without the
off-gated segment.
e) Adjust laser output and/or PMT voltage (see PMT gain curve in Figure
3.2 of reference 3) and/or partially mask receiver objective lens so the
DIRECT lidar signal scope display falls below 1 volt (1/2 scale for + 1 volt
sensitivity setting on TR) at or before the nearest range of interest. If it
is necessary to use PMT voltages below 1500V, then further limit PMT output
at that range to values not exceeding 0.8V for 1400V or 0.7V for 1300V. See
Section 4 for additional information on signal and linearity limits.
Target Ranging and Off-Gate Adjustment
a) With the LSP still in DIRECT mode, aim lidar at target (plume) and
fire lidar shot.
b) Note (on scope) where lidar signal abruptly starts to rise off-
scale.
c) Turn on pulse generator, and depress the +INPUT AC coupling switch
of TR chan B.
d) Press LDP TEST button and note location of positive pulse from pulse
generator.
e) Adjust pulse gen. pulse delay so as to position the start of the
pulse slightly before the scope location previously observed (b above) for
the start of the plume signal. To do this, repeatedly use trial pulse gen.
delay adjustments and check with LDP TEST as in d above.
f) Lightly press the TR Chan B +INPUT DC switch so that it stays out
and the + INPUT AC switch pops out.
g) Again fire lidar at plume target, and confirm that off-gating starts
before the target signal. Make further pulse gen. delay adjustments if
necessary.
h) Adjust pulse gen. pulse width to that smallest width which blocks
the entire target "direct" signal as confirmed by more lidar shots at the
target.
Range-Corrected Lidar Operation
a) With the above off-gated lidar signal still displayed on the scope,
set signal average-indicating cursors A and B (intensified on scope) to
desired locations, as well as to desired width (LDP). A should precede plume
and B should follow plume.
b) Based on the cursor locations, reconsider or confirm the nearest
range of interest as in "Initial Lidar Shots" instruction e.
17
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(a)
(b)
Figure 6. Oscillograms'showing form of typical off-gated lidar signals.
Both oscillograms have sweeps of 1 microsec/division. (a) has
LSP range corrector set for DIRECT display, and TR input range
= +1V. (b) has LSP set for CORR display, gain = 5X, and
flatness = 5.0, while TR input range = +0.2V. Range compensa-
tion starts at N and ends at F, while semi-transparent target
is at t. Note the separate zero trace at the bottom of b.
18
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c) Switch LSP correction mode from DIRECT to CORK, and switch TR chan B
+ INPUT RANGE to + 0.2 volt.
d) Press LDP TEST for scope display of LDP zero (see bottom of Figure
6b).
e) Readjust LSP ZERO ADJ. if desired, and re-check with LDP TEST.
f) Fire lidar at target (plume) to confirm proper off-gating, signal
levels, and operating ranges. See Figure 6b for example of correct result.
g) Check range-correcting ramp length:
o If range compensation does not extend beyond cursor B, increase
length of LSP ramp input.
o If range compensation extends unnecessarily beyond cursor B,
decreasing the length of the LSP ramp input will improve
signal/noise ratio.
o LSP input ramp length is controlled by the scope time base
TIME/DIV. control.
h) Aim and fire lidar at clear air alongside target to further confirm
selection of all parameters.
i) Also note flatness of the total clear air range-corrected signal,
and optimize flatness by adjusting the LSP FLATNESS control. Refire lidar to
obtain result of the adjustment.
Measurements
a) If desired, re-set the LDP ID code number, and press LDP RESET
button.
b) Flip LDP processor switch from INHIBIT to PRINTER OUTPUT.
c) Press PDP TEST 2 or 3 times to record the range-corrected zero.
d) Aim lidar alongside the plume and obtain as many clear air range-
corrected shots as desired.
e) Aim lidar at the plume and obtain as many range-corrected target
shots as desired.
f) Repeat clear air shots if desired.
g) Re-record zero levels by pressing LDP TEST.
19
-------
Lidar System Shut-Down
a) Turn off laser components.
b) Turn off wall circuit breakers for laser PS.
c) Turn off laser cooler (two switches).
d) Turn off all remaining electronic components.
e) Turn off both MG sets.
f) Replace objective lens covers on both transmitter and receiver.
g) Lower lidar and re-position it on lidar travel brace. Bolt lidar
base plate to the travel brace using supplied wing nuts and lock washers.
h) Close and bolt van roof cover.
PLUME DATA ANALYSIS
The LDP-displayed and printed transmittance (Tp) and opacity (Op) are
automatically calculated from the cursor-identified near and far LDP signal
averages A and B, respectively as follows:
Tp = (B/A)1/2 3-1
Op = 1 - Tp 3-2
These "raw" Tp and Op values contain the following errors and uncertainties.
a) Tp is almost always rounded upwards (only) to the next largest
hundredth (thus 0.7307 becomes 0.74).
b) The lowest level signals available from the TR are
A(min)=B(min)=007, and scope(min)=0.20 cm.
c) The range-corrected zero signal levels have A and B usually 008 to
010.
d) Thus the displayed and printed Tp values do not account for the non-
zero zero signal levels.
e) The Tp values also do not include correction for cases where the
clear air reference shots have A^B due to a wrong "flatness" setting or
unusual atmospheric conditions.
All these deficiencies of data reduction are eliminated if transmittance
is fully zero- and air-corrected (Tca) from the LDP-determined A and B
averages as follows:
20
-------
°ca = 1 - Tea 3-3
Tca = Tc(plume)/Tc(air) 3-4
Tc = (Be/Ac)1/2 = [(B - B0)/(A -Ao)]1/2 3-5
Ac = A - A0 3-6
Bc = B - B0 3-7
where AQ and Bo are range-corrected (LSP) zero signal level averages obtained
by pressing LDP TEST as previously instructed.
21
-------
SECTION 4
SPECIAL INSTRUCTIONS AND PRECAUTIONS
MOTOR GENERATOR USAGE
The van contains two motor generators (MG) and two power distribution
systems, with the capability of connecting either MG to either wiring system.
This way, the more sensitive items can be powered separately from those items
with large variations in power consumption.
Even though the lase.r used for this lidar system has been modified by
the manufacturer to significantly reduce peak power consumption compared to
an unmodified version, the laser power supply (PS) still draws heavy current
during capacitor charge-up (see Table 1). Thus the laser MG output undergoes
large voltage variations and should not be used to power the other
electronics or even the laser Pockels cell PS. However, the laser water
cooler may be powered off the laser MG provided that the cooler's water
circulation pump and its thermal control system are powered by opposite sides
of the laser MG power line. In any case, the laser manufacturer emphatically
states that the laser power line voltage must not continuously exceed 230
volts.
Therefore the following MG usage is recommended:
a) Power the laser and water cooler off one MG. The cooler should be
operated in split mode (mode switch is on back of cooler), with the cooler's
water pump and thermal control being powered from opposite sides of the MG
power line.
b "S Power all other items (including the laser Pockels cell power
supply) off the other MG.
c) Since the laser power line must not continuously exceed 230 VAC (115
VAC each side), the line voltage applied to the laser PS should be checked,
and if necessary adjusted, before power is applied to the laser and also
during "idle" operation of the laser.
LASER PRECAUTIONS
Laser Line Voltage Limits
Successful laser operation depends on the laser power supply line
voltage being within the relatively narrow range of 210-230 VAC. In fact, the
laser manufacturer states that line voltage continuously above 230 VAC will
cause failure of certain laser PS components. Thus the laser PS line voltage
22
-------
must be carefully controlled and monitored as more fully discussed above.
Laser Output vs. Input
For lasers of this type, the laser output is a very sensitive function
of flashlamp voltage increment (AV) above the lamp voltage for lasing
threshold (Vt). During laser and lidar tests, Vt was found to be 4.2-4.5 kV
(usually 4.3-4.4 kV) depending on coolant temperature, state of laser
alignment, and Pockels cell adjustment. During the same tests, laser output
has been found to typically be about 0.5, 1, and 1.5 joules/pulse for AV
about 0.2, 0.5, and 0.8 kV above threshold, respectively. At this rate, AV =
2 kV above Vt could yield over 3 joules/pulse. Outputs significantly over 2
joules/pulse endanger laser optics due to very high optical power densities.
Since the laser PS can be pre-set as high as 10 kV (5.6 kV over Vt), the
laser could be accidently pre-set so the optical power density from even a
single laser shot could severely damage the laser optics or its ruby rod.
Note that the above-listed Vt and output vs AV values indicate a lower
threshold and an output more sensitive to lamp voltage than shown on the
manufacturer-supplied data sheets. Thus it is suggested that the laser user
not rely solely on the manufacturer data sheets to pre-set the laser
flashlamp voltage.
Laser Coolant Precautions
During laser operation, cooling water temperature preferably should not
be less than 20°C, as laser output will increase with decreasing ruby rod
temperature. In addition, the water-cooled laser cavity must always be
operated at a temperature greater than the local dew point in order to
prevent condensation on the laser and its optical surfaces.
Do not subject the laser system to temperatures such that the cooling
water could freeze. If storage in sub-freezing temperatures is unavoidable,
thoroughly drain all water from the laser head and remove the water from the
laser cooler.
In general, the Neslab cooling system will require only periodic
inspection to verify that the distilled water is clean and clear, free of any
trace of cloudiness or color. If water contamination becomes too severe, it
can necessitate the replacement of the laser's helical lamp and reflector. It
is a good practice to replace both water and deionization filter (Barnstead
mixed Resin No. D0809) every year, regardless of usage of system. Also,
during periods of non-use, circulate the water for at least an hour a month.
If the clear flexible water tubing between cooler and laser ever develops an
inner coating (such as green algae), replace it with clear Tygon S-50-HL
tubing, 3/8 inch bore, 3/32 inch wall.
23
-------
LASER SPECIAL PURPOSE INSTRUCTIONS
Laser Interlock Locations
After the laser PS wall plug is powered and the laser turned on, if the
laser remote station interlock light (next to shutter switch) remains on, the
laser interlock line is open and the laser will not operate. Interlock
switches are located at the main PS door, the main PS side panels (top
center), the laser cooler (water pressure sensor), the lidar laser cover (top
front), and the lidar transmitter objective lens tube where it attaches to
the support plate. Interlock external (white) line plugs are located inside
the main PS, on the laser cooler side, and at the lidar base plate bottom.
Auxiliary Laser Connectors
The laser contains BNC connectors with sometimes useful special purpose
inputs/outputs as follows.
Back of Remote Station Control Unit—
a) J2 fires laser (if already charged) when apply +15V.
b) J3 supplies +15V when laser fully charged (normally and as
delivered, J2 is jumpered directly to J3).
c) J4 is a +15V safety interlock. Ground J4 to remotely prevent
charging or to discharge capacitors.
d) J5 is normally +15V. Ground J5 to remotely charge and fire laser.
Back of Q-Switch Remote Control Unit—
a) J2 receives +20V pulse from J12 of the laser power supply when the
flashlamp is triggered.
b) J3 supplies +30V pulse about 250 nsec before the laser lases.
Inside Laser Main Power Supply—
J12 supplies +20V 10 microsecond pulse when the flashlamp is triggered.
Use of Laser Monitor Integrating Load
When it is desired to measure laser output without use of the LDP or
more accurately and reproducibly than is possible via the LDP, or if it is
desired to check for the quality or timing of the laser output, then the
laser monitor integrating load from the original lidar system can still be
used in the same manner as in the past[5]. To make this type of laser output
measurement, the oscilloscope is used in real time as follows:
24
-------
a) Move the RG 62/U coaxial cable from LDP monitor IN to original
monitor load box set for ENERGY, which is to be connected to scope "left
vert, input".
b) Set the scope vertical amplifier to 0.1 V/div. or 50 mV/div.
c) Convert the scope to normal operation by depressing "horizontal mode
B". This brings the scope time base unit into play.
d) Set the time base unit to mode = NORM, coupling = AC, source = LINE,
level/slope = 10:00, display mode = TIME BASE, and sweep = "50 ys/div.".
e) Turn on both the scope and the LSP.
f) Adjust scope zero and "B intensity".
g) Switch the scope time base source to INT.
h) Operate the laser (see Section 3) and observe the real-time wave
form on the scope.
The wave form should show a single step rise. For laser output energy,
refer to the separately supplied "Laser Energy Monitor Calibration" dated
3/9/79. Occasionally during weak lasing, there is a second weaker pulse about
10 microseconds after the first, causing a two step rise in the waveform.
LIDAR SIGNAL AND LINEARITY LIMITS
The lidar PMT detector is still the same as described in reference 3,
and the LSP range correction circuit still has the same basic design as in
reference 3. However, there are now differences in operation.
Range Corrector Operation
The LSP range corrector operational requirements are the same as
described in reference 3, except that (a) the far range limit (F) for
correction is now selected differently due to a different ramp source, and
(b) the criteria for judging the near range limit (N) for correction are
somewhat modified as described below.
As indicated in Section 3, the limit F is determined by LSP input ramp
length which is controlled by the oscilloscope 7B50 time base unit "time/div"
switch. If continuous control is desired,the 7B50 can be switched to
continuously variable operation by snapping the "time/div" central button to
its out position. It should be remembered that the LSP range-correcting
circuit yields highest signal/noise results when it is used such that range F
does not greatly exceed the maximum far range needed.
The near range limit (N) for linear range compensation is never closer
than the nearest range at which the receiver "sees" the entire laser beam
(discussed later). As before, if the PMT output and range corrector gain are
both such that the output of the A2 linear amplifier (93 ohm input) reaches
25
-------
10 volts and is held there by its overvoltage-protecting feedback diode, the
near range limit N for range compensation is delayed until the linear
amplifier output again drops below 10 volts due to increasing signal range.
However when this situation is now being set up as described (for 5X gain) in
Section 3 for initial lidar shots, the PMT output is first observed with the
LSP set for DIRECT. Thus the direct signal voltage [V(dir)] is observed
across the transient recorder's 50-ohm (not 93-ohm) input load, causing
V(dir) to be (50/93) as large as input voltage to the range corrector.
Consequently, for LSP-limited range, N is that range at which the following
product drops to 10 volts:
V(dir) x gain x (93/50) = 5.6 V(dir) for 3X gain
=9.3 V(dir) for 5X gain
= 18.6 V(dir) for 10X gain
As reviewed below, for best results do not allow the PMT to be operated
with non-linear output beyond the near range point N.
Detector Linearity
As detailed in reference 3, for the intended type of lidar use the PMT
linearity is space-charge limited. Table 5 summarizes some results from
reference 3. The Table 5 values listed under "LSP direct" are for a 50-ohm
load, while the "LSP corr" values are for a 93-ohm load.
TABLE 5. DETECTOR SPACE CHARGE-LIMITED LINEARITY
Deviation )
from linearity j
PMT
Volts
1300
1400
1500
1600
1700
1800
1900
2000
Max
Current
(ma)
14
17
19
23
26
29
32
37
$2%
Max
LSP
Direct
0.70
0.83
1.0
1.1
1.3
1.4
1.6
1.8
Volts
LSP
Corr .
1.3
1.5
1.8*
2.1
2.4
2.7*
3.0
3.4
Current
(ma)
17
20
23
26
29
32
36
40
5%
Volts
LSP
Direct
0.86
1.0
1.1
1.3
1.4
1.6
1.8
2.0
LSP
Corr
1.6
1.8
2.1*
2.4
2.7
3.0*
3.3
3.7
*Note: The actual measured values are starred. All other values are obtained
from interpolation, extrapolation, and calculation.
The optimum applied voltage is that which yields a nearest range signal
maximum equal to or somewhat larger than the PMT space charge linearity limit
26
-------
(see Table 5) since this will allow maximum system range. This applied high
voltage is determined empirically by observing the lidar signal at range N
and adjusting the PMT voltage until the desired linearity condition is met.
The voltage required may vary from day to day depending on ambient aerosol
scattering and on the laser output energy. Another means for reducing PMT
output is by masking down the receiver telescope or by reducing laser output.
LIDAR RECEIVER-TRANSMITTER ALIGNMENT
The lidar system is aligned by moving the receiving system optical axis
with respect to the transmitting system axis by means of bolt-lockable
adjustments under the receiving telescope[5]. Alignment adjustments should
not be generally necessary because of the rigidity of the design coupled with
the relatively wide field-of-view of the receiver (4 mrad full angle)
compared with the <0.5 mrad full angle lidar transmitter output divergence.
In order for the lidar system to have complete overlap between the
transmitted laser beam and the receiver field-of-view (fov) for ranges over
150 meters, a geometric analysis shows that for this lidar system the
receiver and transmitter optical axes must intersect at a finite distance
rather than at infinity (parallel optical axes). This analysis yields the
following results, where Rc is convergence distance of the receiver and
transmitter optical axes, while Rn and Rf are the corresponding near range
and far range, respectively, for complete overlap between the transmitted
laser beam and the receiver fov.
Rc Rn Rf Units
160 91 infinity meters
200 101 >infinity meters
300 118 >infinity meters
400 130 >infinity meters
762 150 >infinity meters
infinity 181 >infinity meters
The lidar system was delivered with Rc = 300 m and receiver telescope focused
for 300 m, yielding full receiver-transmitter overlap for ranges >120 m. The
aiming riflescope is aligned parallel to the receiving telescope axis.
To check system alignment, the lidar system should be aimed at a
diffusely reflecting light-colored target surface about 300 meters away. At
that range, the lidar receiver and laser transmitter axes should be
coincident, while the riflescope should be aimed about 12 cm to the left of
that common point. This can be confirmed by firing the laser and noting the
location of the red spot on the diffuse target through both the riflescope
and also through the receiver[5] collimating lens (L4 of Figure 3). Also
confirm the receiver telescope focus for the target distance.
If the system alignment should need adjusting or if a different
convergence (target) distance is desired (200-500 m recommended), the lidar
27
-------
receiver-riflescope combination may be moved with respect to the laser and
re-secured via the lockable pivots and bolts below the receiver telescope [5].
The riflescope cross-hair may be moved with respect to the receiver telescope
via its internal screw adjustments.
If it is ever desired to align the system axes at infinity, it is useful
to have a gridded diffusely reflecting target with 4 cm squares marked off
(white painted plywood for example). This target is then placed at a range of
at least 60 meters and viewed through the receiving system. The riflescope
should then be adjusted until its cross-hair is on the receiving system axis
vertically, and approximately 12 cm (3 spaces) displaced horizontally to the
left. The riflescope and receiving system axes are now parallel and will move
together during any further receiving system adjustments. Next the laser
should be fired and its position on the diffuse target noted through the
receiving system. The receiving system should then be adjusted until the
laser pulse is on the receiving .system axis vertically and is 20 cm (5
spaces) to the right horizontally. (Note that since the receiving telescope
provides a reversed view, a feature on the right will appear to be on the
left.) Now all three optical axes are aligned at infinity.
28
-------
SECTION 5
LASER MONITOR
This monitor detection system provides both the time zero (trigger)
information and laser output energy information for the entire lidar system.
As shown in Figure 7, the laser monitor consists of a PIN-3D silicon
photodiode which measures the laser light scattered from the laser output
window (OW). This photodiode is located in the laser output window support
structure together with a 100A wide narrow bandpass filter (NB) to
discriminate against laser flashlamp light, and a 0.2 optical density neutral
filter (NF) to adjust the monitor sensitivity. Still refering to Figure 7,
the photodiode is biased to -15 volts DC from the LSP box where it is
capacitively coupled to whichever supplied monitor load is used, or to any
93-ohm load.
29
-------
In LSP ("laser monitor")
200K
0.1
"laser in"
PIN-3D
RG 62/U
NF
VDC
"sig. out"
TO:
LDP "monitor in"
or
integrating load
or
93 ohm load
B
F
-
\ OW
^
1
On
Laser
at
scope
input
Figure 7. Laser monitor and monitor bias circuit,
30
-------
SECTION 6
LIDAR SIGNAL PROCESSOR
As indicated in Section 1, the previous version of this lidar system[l-
3] employed a range-compensating "time squared amplifier" (TSA)[3] to aid the
lidar measurement of smoke plume opacity. However, this lidar refurbishment
has resulted in so many system changes, that the original form of TSA is no
longer compatible with the other components of the lidar system. The old
lidar system used real time signal display on an oscilloscope which also
provided a high voltage ramp for the TSA, while the refurbished lidar employs
a non-real time scope display. Also, the old lidar system had the TSA output
go to a high impedance load (scope), while the refurbished lidar has the
range-correcting output go to the 50-ohm input of a transient recorder.
These lidar system changes have been accommodated by a redesigned "lidar
signal processor" (LSP) range-correcting circuit. This LSP package also
contains the laser monitor power source and coupling capacitor shown in
Figure 7. Figure 8 shows the LSP front and rear panels, while Figures 9, 10,
11, and 12 show the LSP circuit diagrams.
As indicated by Figure 4 and instructed in Section 4, the range-
correcting TSA ramp is still obtained (via RG 62/U cable) from the
oscilloscope time base unit, but that time base unit is now operated
independently of the scope X-Y display. The resulting ramp length ("far
limit" control) is adjustable at the scope time base unit, but amplifier Al
(Figure 10) had to be added to the TSA to increase the ramp amplitude and to
allow the inclusion of a ramp DC bias ("flatness") control. Since the final
multiplier M2 (Figure 11) has a somewhat limited maximum output current
capability plus a too severely reduced frequency response near its upper
limit of output current, a high output current high frequency amplifier A3
(Figure 12) has been added after multipler M2 to act as a booster amplifier.
The range-correcting signal output now must be terminated at any 50-ohm load,
such as the transient recorder supplies.
The resulting modified range-correcting circuit has been measured to
have 5-6 MHz frequency response for all signal output amplitudes to about 3
volts (max) across a 50-ohm load such as found at the transient recorder
input. The measured 10% to 90% rise and fall response times (Tr and Tf
respectively) are listed below for both medium and large amplitude outputs
into a 50-ohm load.
31
-------
t
UDAR SIGNAL PROCESSOR
r-PO'WER-i
I I
€L_
-LASER MONITOR]
RANGE COR8E<
»tN
3K 5X IOX
LASER SIG,
IN OUT
L' tnn
'*»**»
ZERO f'W
A0J. iN
105-i25 VAC
47-440 HZ
Figure 8. Lidar signal procsssor (LSP) front (top) and rear (bottom) panels.
32
-------
LASER MONITOR-
iASER IN 5/S-. OUT
i£. our
[—(7)
V rg
I DDK
I
T7
10
15
D/'RECT
CO
^
OAR
— >-
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i i
T3
i
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5
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i IS
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Lt J
Lw\k/-— 1
25 K
ZE^O ADJ.
T9
i
•^
CARD 2
^ r5+]SV*
i
.
G
/5
fl)RAMP
|N
30O
(TH-
3OO
GAIN 5X
300
300
10 x r
-Ho COM, -f5
Figure 9. Lidar signal processor (LSP) circuit diagram for card receptacles and end panels
-------
-15 V
f
+ I5V
13V IN
-------
OJ
Ln
(77)
(T6)
(73)
(TV)
:'3<-
14-
:<*<-
J'6K
<£-
\
'/of
?/
-vyyv
//V^/^
-40-
-15 V
M-
i—W— ^70K
?/
V
T3
IN \A2
A522^^OWT
T6
w
Y
V
COM
N2
M506^>^r
(+)
-T7
+/^:
IM
-15
|M
10:
10
V
-H5V-/5V
CARD
Figure 11. Lidar signal processor (LSP) circuit diagram for card 2 (center card).
-------
300
1-20
(T-
'(TOP
Figure 12. Lidar signal processor (LSP) circuit diagram for card 1 (top card)
-------
LSP Corrector "SIG. OUT"
LSP Amplitude Tr Tf
Gain (volts) (nsec) (nsec)
3X -0.5 60 59
5X -0.5 60 59
10X -0.5 76 77
3X -2.5 61 55
5X -2.5 61 55
10X -2.5 76 71
Since the LSP range correcting is based on the ISA design of reference 3, the
various ISA discussions of reference 3 still apply except as modified above
and in Section 4.
37
-------
SECTION 7
SCREEN TARGET TESTS
After the refurbished lidar system was made operational, opacity
measurements were made of six semi-transparent screen targets from ranges of
190-225 meters. The GFE screen targets used for these tests were supplied
mounted with clear apertures of 1.12 meters diameter, and numbered 12, 14,
24, 32, 43, and 52. They have wire spacings ranging from about 2.6 cm for
#12, to 1.7 cm for #14, to less than 0.2 cm for all the other screens.
Similar to the target tests of reference 3, the screens were supported
by a wood structure placed on the roof of a small building at the General
Electric Valley Forge Space Center. The van was located southwest of the
targets and about 220 meters away for all but the last tests (screen #12)
which were made from a distance of about 190 meters. Due to adjacent
interferences, measurements were restricted to those days with winds from the
southwest (through west and northwest) to from the north. Unfortunately the
entire month available for testing was a period of unusually bad weather,
with winds generally from the wrong directions and rain or fog almost daily.
There were a few weather "windows" during which measurements were made, but
even then, high velocity southwest winds apparently produced a turbulence-
induced dust plume "tail" which extended far enough behind the target
building to invalidate most shots made on two of the days.
Finally, all but the last set of runs had considerable electrical
interference from laser Pockels cell (PC) noise. While this pickup noise
degraded the lidar signal appearance (oscilloscope display), the LDP A and B
averages were not severely affected due to the large number of data points
(40 and 100) used for the averages. Before the last screen target runs, that
PC pickup had been significantly reduced (see Figure 6b) through selective
changes in PC cable routing and suitable changes in incidental grounds.
The general data acquisition method after establishing laser and lidar
operating conditions (see below) was to obtain and record (printer) the lidar
zero signal (via LDP TEST) and then run and record a series of screen shots
while observing the lidar signal displays on the oscilloscope screen. As each
lidar signal was displayed (for at least 4 seconds), a good or bad data
judgment was made based on general signal shape only, and the "bad" shot
numbers noted for later discard during data analysis. As stated above, on two
of the days most shots were bad. Similarly, a series of clear air lidar shots
were obtained and judged while aiming alongside the screen target holder.
Oscillograms were also made from some of the scope displays, as well as of
the related zero-signal displays.
38
-------
All of the screen target and associated clear air shots were made with
the following lidar system operating conditions.
laser output = 0.3-0.7 joules/shot
PMT volts = 1300-1500 volts
PMT off-gate width = 500 nsec
LSP gain = 5X
LSP ramp length = 4 and 5 microseconds
Sample interval = 10 nsec
LDP A avg. = 40 samples wide and located just before
the off-gate, period
LDP B avg. = 100 samples wide and centered 1.5-2.0
microseconds after the target
The results of these screen target tests are summarized in Tables 6 and
7. Table 6 shows the averaged results of raw (T_) and zero-corrected (Tc) LDP
transmittances for each set of screen target and associated clear air shots,
as well as clear air-corrected target transmittance (Tca) and opacity (Oca) .
See Section 3 for definitions and equations.
Table 7 provides a comparison of screen (and air) transmittance as
manually measured from lidar signal oscillograms (Ts), vs. LDP-assisted
screen (and air) transmittance for the exact same shots. The LDP values are
shown as separately calculated raw (B/A)!'2, as directly presented raw Tp,
and as zero-corrected Tc values (see Section 3). As shown by the (Tp-Ts) and
(TC-TS) columns of Table 7 and by the average (T-TS) values at the bottom of
the table, it is clear that the transmittance values manually measured and
calculated from oscillograms (Ts) agree best by far, with the LDP zero-
corrected (Tc) values. A comparison of Tp with (B/A)^-'2 also shows that the
LDP transmittance value presented is usually the next highest hundredth, not
the nearest hundredth.
In conclusion, it is recommended that the data analysis method of
Section 3 will give the most accurate result over the broadest range of
circumstances.
39
-------
TABLE 6. SCREEN TARGET AND AIR TRANSMITTANCES
FROM LIDAR DATA PROCESSOR(LDP) DATA*
Target
(air or scr. //)
#52
air
#43
air
#32
air
#32
air
#24
air
#24
air
#14
#12
air
# Shots
Tot.
9
9
40
14
40
12
27
18
30
17
42
11
26
13
8
OK
9
9
3
13
16
11
3
10
7
17
26
11
25
11
8
"OK" Averages
T (raw)
P
0.490
1.002
0.530
1.033
0.679
0.988
0.687
1.035
0.760
0.995
0.757
0.972
0.881
0.887
1.015
T
c
0.413
0.991
0.466
1.032
0.644
0.982
0.660
1.036
0.720
0.983
0.726
0.958
0.855
0.866
1.008
T
ca
(fully corr.)
0.417
0.452
0.655
0.637
0.733
\ 0.758
} 0.893
0,859
Opacity
0
ca
0.583
0.548
0.345
0.363
0.267
0.242
0.107
i
0.141
*From Section 3, we have the lidar results and definitions:
T = LDP "raw" (uncorrected) transmittance
P
T = zero signal level-corrected transmittance
T = zero level-corrected and clear air-corrected transmittance
ca
0 = opacity = 1 - T
ca ca
40
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TABLE 7- COMPARISON OF OSCILLOGRAM TRANSMITTANCE (Tg) WITH
SAME-SHOT LIDAR DATA PROCESSOR(LDP) TRANSMITTANCES
Target
(air or scr. //)
#52
air
#43
air
#32
air
#24
air
#14
#14
#14
air
#14
air
#12
air
T
s
(scope)
0.420
1.012
0.474
1.013
0.655
0.993
0.704
1.004
0.848
0.844
0.828
1.029
0.885
0.992
0.876
1.011
F
/B/A
0.482
1.013
0.542
0.694
0.991
0.728
1.007
0.864
0.860
0.844
1.030
0.890
0.992
0.885
1.031
rom LDP*
I~T "
P
0.49
1.02
0.55
0.70
1.00
0.73
1.01
0.87
0.86
0.85
1.03
0.90
1.00
0.89
1.03
T
c
0.417
1.009
0.476
0.664
0.986
0.700
1.000
0.847
0.837
0.831
1.028
0.883
0.987
0.869
1.030
average screen (T-T )
s
average air (T-T )
S
(T -T )
P s'
+0.070
+0.008
+0.076
+0.045
+0.007
+0.026
+0 . 006
+0.022
+0.016
+0.022
+0.001
+0.015
+0.008
(T -T )
c s
-0.003
-0.003
+0.002
+0.009
-0.007
-0.004
-0.004
-0.001
-0.007
+0.003
-0.001
-0.002 ;
-0.005 |
+0.014 -0.007
+0.019 +0.019
+0.034
+0.008
-0.001
0.000
*See Section 3 or Table 6 for definitions of transmittances T and T ,
P c
as well as of A and B.
41
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REFERENCES
1. C.S.Cook, G.W.Bethke, and W.D.Conner, "Remote Measurement of Smoke Plume
Transmittance Using Lidar," Applied Optics 11, 1742 (1972).
2. C.S.Cook and G.W.Bethke, "Design, Construction, and Evaluation of a
Mobile Lidar System for the Remote Measurement of Smoke Plume Opacity,"
EPA Contract No. 68-02-0093, Final Report, Report No. APTD-0968, December
1971.
3. G.W.Bethke, "Development of Range Squared and Off-Gating Modifications
for a Lidar System," EPA-650/2-73-040, December 1973.
4. "Lidar Data Processor Technical Manual," EPA Contract No. 68-02-1291,
December 1977.
5. "Mobile Lidar System Operating Manual," EPA Contract No. 68-02-0093,
January 1972.
42
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TECHNICAL REPORT DATA
(Please read Instructions on the i:f verse before compL
REPORT NO.
EPA-600/2-79-197
4. TITLE AND SUBTITLE
MOBILE LIDAR SYSTEM DEVELOPMENTS AND
OPERATING PROCEDURES
6. PERFORMING ORGANIZATION CODE
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
November 1979
7. AUTHOR(S)
G. W. Bethke
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
General Electric Company
Space Division, Space Sciences Laboratory
P. 0. Box 8555
Philadelphia, Pennsylvania 19101
10. PROGRAM ELEMENT NO.
1AB712 BC-09 FY-78
11. CONTRACT/GRANT NO.
68-02-2979
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory - RTP, NC
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N. C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final 9/78-5/79
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A smoke plume opacity-measuring mobile lidar system was refurbished, modified,
and tested on semi-transparent screen targets. This refurbishment has involved
retrofitting a new laser to a previously existing lidar transmitter/receiver,
designing and fitting a new laser monitor to the laser, modifying and rebuilding
the range correcting signal processor to be compatible with the other mostly
new lidar components, installing all the lidar components into a new and larger
van, and finally getting the entire system to function together and become
operational. The resultant lidar system automatically analyzes, presents, and
records smoke plume data, resulting in a much faster data rate and easier
analysis than was formerly possible with the earlier versions of this lidar
system. Complete operating procedures for the improved system are presented.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATl Field/Group
* Air pollution
* Plumes
* Opacity
* Remote sensing
* Optical radar
* Mobile equipment
13B
2 IB
14B
17H
15E
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
49
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
43
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