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

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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

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                                  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

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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

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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

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(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

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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

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                                  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

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     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

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                                  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

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                     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

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                     LASER    MONITOR-

                      iASER IN    5/S-. OUT
       i£. our

        [—(7)
       V   rg
                                  I DDK
                                  I
                                                  T7
                                       10
                                                    15
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-,5-yc-c - T2 T6
i i












T3
i


P
- i "I
                            5
                                         10
i  IS
       IN


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
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                                               i—W— ^70K
          ?/
                                                      V
                     T3
     IN    \A2

        A522^^OWT
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         w
            Y
                                       V
                                                                    COM
           N2

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                                                                                      -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)

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                            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

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                                  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

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              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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