EPA-600/4-76-028
June 1976
Environmental Monitoring Series
AIRBORNE LIDAR RAPS STUDIES, FEBRUARY 1974
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
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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 five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/4-76-028
June 1976
AIRBORNE LIDAR RAPS STUDIES, FEBRUARY 1974
by
John A. Eckert, James L. McElroy
Donald H. Bundy, John L. Guagliardo and S. H. Melfi
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
U.S. ENVIRONMENTAL PROTECTION AGENCY
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and
Support Laboratory-Las Vegas, U.S. Environmental Protection Agency, and
approved for publication. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
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CONTENTS
Page
Introduction 1
Objectives and Approach 1
Results and Discussion 2
References 17
LIST OF FIGURES
Number Page
1 Diagram of airborne LIDAR system 5
2 Map of LIDAR traverses, February 23, 1974 6
3 Helicopter profile over Spirit of St. Louis Airport,
February 23, 1974 7
4 Iso-scattering contour plot, east to west traverse,
February 23, 1974 8
5 LIDAR profile showing Labadie plume, February 23, 1974 ... 9
6 Iso-scattering contour plot, south to north traverse,
February 23, 1974 10
7 Map of LIDAR traverses, February 25, 1974 11
8 Iso-scattering contour plot, south to north traverse,
February 25, 1974 12
9 Iso-scattering contour plot, west to east traverse,
February 25, 1974 13
10 Helicopter profile over Gateway Arch compared with LIDAR
signal, February 25, 1974 14
LIST OF TABLES
Number Page
1 System parameters 15
2 Testing periods 16
i i i
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INTRODUCTION
Current techniques for measuring mixing layer height involve both
direct and remote sensing techniques.1 Direct measurements are typically
made by radiosondes, a technique which is rather expensive per temperature
profile obtained and, therefore, not generally used in situations requiring
high spatial or temporal resolution. The principal advantage of the tech-
nique is that radiosondes provide a direct reading of the temperature,
independent of humidity or particle loading. Direct measurements are also
made with temperature sensors mounted on various aircraft. Remote moni-
toring techniques include acoustical sounders which provide high temporal
resolution, but are seldom used in other than fixed locations. Acoustical
techniques, however, are dependent on humidity as well as temperature,
and are subject to false traces due to extraneous noise sources and, thus,
at least at present, skillful interpretation of the results is necessary.
Light Detection and Ranging (LIDAR) devices have been used for
measuring mixing height from fixed and mobile platforms.2 These devices
depend on scattering from aerosols trapped within the boundary layer.
This method of measuring the mixing height requires that the tracer
aerosol scatter the signal at the inversion interface. Other limitations
include the high capital cost of the device and a need for skillful
interpretation of the data. At the present time, however, the airborne
LIDAR appears to be the only feasible method of measuring the height of
the boundary layer over large geographical areas in relatively short
time periods.
During February 1974, an airborne downlooking LIDAR system was flown
in support of the Regional Air Pollution Study being conducted by the
U. S. Environmental Protection Agency (EPA) in St. Louis, Missouri.
The LIDAR system was used primarily to measure mixing layer height over
the metropolitan area during the morning and evening transition periods.
The flight plan consisted of south to north and west to east traverses
with horizontal data resolution of 1.5 kilometers and a vertical resolu-
tion of 30 meters. (One traverse over the greater St. Louis area could
be flown in about 10 minutes.) Final data are presented in computer-
generated, iso-scattering curves plotted in altitude versus ground-
distance along the particular traverse.
OBJECTIVES AND APPROACH
The purpose for participation in the St. Louis studies was twofold.
First, it was desirable to obtain data on the height of the boundary
layer during the morning and evening transition periods. Data have
1
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been reported in the literature with measurements made at a limited
number of fixed locations.3 It was hoped that airborne LIDAR data
would enable experimenters to extrapolate results from fixed sampling
locations with high temporal resolution to obtain modeling information
covering the entire St. Louis metropolitan area. The second objective
was to compare airborne LIDAR results with radiosonde measurements and
other in situ monitoring methods.
A system chart is shown in Figure 1. Basic design criteria included
a variety of constraints imposed by aircraft power and safety considerations.
The aircraft used was a C-45 (twin-engine Beechcraft) operated by
the EPA. The aircraft has an aerial camera port and the telescope/laser
assembly was designed specifically to the dimensions of the port, 45
centimeters (cm) by 50 cm. To reduce the weight of the system, the laser
power supply was repacked into two aluminum boxes conforming to aircraft
safety requirements. Weight reduction on the power supply alone amounted
to about 180 kilograms (400 pounds). The telescope was made using air-
craft construction techniques and utilized a plastic Fresnel lens as the
light collecting element. Data output from the system was through a fast
analog to digital converter. Final data output was on strip charts which
were subsequently hand digitized and analyzed using a large digital com-
puter at the Las Vegas Laboratory. Table 1 is a summary of the design
parameters.
Comparison data were obtained from in situ monitoring instrumentation
located in a mobile van and a helicopter. Instrumentation on both the
helicopter and the panel van was the same and consisted of a sulfur dioxide
monitor, temperature and humidity sensors, and an integrating nephelometer.
Meteorological data were also obtained with radiosondes released during
each of the test periods at several fixed locations including the Arch.
Wind profiles were obtained both at the Arch and at a rural site.
RESULTS AND DISCUSSION
A total of 10 flight profiles was obtained during three days of
operation. A log of the testing periods is shown in Table 2.
Discussion of the results of the LIDAR flights will concentrate on
the urban plume studies of February 23, 1974, and the late evening
traverses conducted on February 25, 1974. Extensive meteorological data
were obtained during these periods by helicopter, by a mobile van and by
ground-based observers at two fixed locations.
1. February 23, 1974
Three traverses were made late in the morning of February 23
to define the dimensions of the urban plume.
Clear skies and low wind velocities on the afternoon and evening
of February 22 permitted the formation of a surface-based inversion which
did not break up until the afternoon of February 23. Mid-morning warm
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air advection enhanced the intensity of the inversion layer resulting in
a decision to fly a series of traverses over the anticipated urban plume.
The winds during the plume study were east-southeast at the ground veering
to southeast near the top of the mixed layer. Wind speeds increased
slightly from 5-6 meters/second near the surface to 6-7 meters/second at
the top of the mixed layer.
Figure 2 shows the flight traverses,wind vectors at the ground
and top of the inversion layer, and the location of ground sites where
temperature profiles were obtained. The temperature profile taken at
site (4) which was located at the Spirit of St. Louis airport is probably
the most representative of the character of the mixed layer at the time
the LIDAR measurements were taken (Figure 3). Note the well-defined
inversion at 900 meters mean sea level (MSL) with a small'kink in the
profile at 300 meters MSL, probably representing a convective bubble.
Figure 4 is a computer-generated iso-scattering contour plot
of LIDAR data taken on the east to west traverse shown in Figure 2.
Aerosol scattering is evident throughout the mixed layer and the depth
is consistent with the inversion height of 900 meters in Figure 3. Small
areas of increased scattering are seen at either end of the plot and
represent emission plumes for power generating plants in the area. The
high scattering region over St. Louis was caused by the plume of a power
plant located near Baldwin, Illinois, some 60 kilometers southeast of
St. Louis. The plume was trapped by the 900-meter inversion and with
the principal scattering occurring in a region about 100 meters thick.
At the opposite end of the traverse, a region of increased scattering
is noted corresponding to the plume from the Labadie power plant (see
location of Figure 2). LIDAR profile number 33 is shown in Figure 5
which shows the Labadie plume to be some 100 meters thick with increased
and uniform scattering throughout the remainder of the mixed layer.
A north to south traverse was flown from Troy, Missouri, to
Washington, Missouri (see Figure 2). Figure 6 is the iso-scattering
contour plot of data obtained on this traverse. Boundary layer thickness
and scattering distribution are similar to the east to west traverse with
the Labadie plume appearing as a region of greatly increased scattering.
The large area of increased scattering shown to the left of the figure
probably represents the urban plume and is consistent with meteorological
data and the location of industrial sites to the east of St. Louis.
2. February 25, 1974
South to north and west to east traverses were made over the
St. Louis metropolitan area during late evening of February 25. Figure
7 is a map showing the location of the traverses, location of individual
laser firings, ground-based sampling locations, and the surface wind
vector.
Skies over St. Louis were clear for the entire day and snow
remained on the ground from a snowfall which occurred February 24.
Outgoing terrestrial radiation aided by the snow cover produced a strong,
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shallow, surface-based inversion in spite of the strong winds. At the
time of the flights, both the surface inversion and a slight inversion at
900 meters MSL were observed. The elevated inversion probably represents
the extent of the maximum mixing depth on that day. A shallow mixed
layer was observed over the urban areas capped by an isothermal layer
Surface winds coming from the west shifted to the southwest in the
evening and diminished in strength.
Figure 8 is an iso-scattering contour map of the south to north
traverse. The upper scattering contour represents remnants of the mixed
layer from that day which had risen to between 800 meters and 900 meters.
The area of increased scattering near the point of intersection of the
traverses represents the plume from the Labadie power plant located
southwest of the city. Increased scattering is also noted near the surface
and probably represents aerosols generated within the urban area.
4
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BIOMATION ADC
FILTER
STRIP
CHART
TELESCOPE
DIGITIZE
& PUNCH
CARDS
CONTOUR PLOT
CDC 6400
Figure 1. Diagram of airborne LIDAR system
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36«
37«
38
39*
40
41
42
^
43'
44
45'
46
47
48
49
50
51
_52
l3
54
55
564
ST. LOUIS
EXPERIMENT
FEB. 23, 1974 1200 HRS.
SURFACE
5-6 "-^
M/S ^
ALOFT
y6-7 M/S
-A WINDS
SCALE (KILOMETERS)
31 30 29 2F/ 27 26 25 24 23 2*2 2*"
DPOWER PLANT
SPIRIT
OF
'ST. LOUIS)
AIRPORT
FERGUSON
,- UNIVERSITY
-: CITY
LOUIS
16 15 14- M~3 f2
kKIRKWOOD
WEBSTER
GROVES
Figure 2. Map of LIDAR traverses, February 23, 1974
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co
Of.
1000-
900-
800-
700-
600-
O 500-
400-
300-
200- SFC-
100-
-4
i
0
-3 -2-101
TEMPERATURE, °C
Figure 3. Helicopter profile over Spirit of St. Louis Airport,
February 23, 1974
7
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00
60 MISSOURI 40
RIVER
30 20
AIRCRAFT GROUND POSITION, KM
10 MISSISSIPPI
RIVER
Figure 4. Iso-scattering contour plot, east to west traverse,
February 23, 1974
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ALTITUDE (METERS)
Figure 5. LIDAR profile showing Labadie plume, February 23, 1974
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45 40
35 30
25
20
15
10
5 MISSOURI
RIVER
AIRCRAFT GROUND POSITION, KM NORTH OF RIVER
Figure 6. Iso-scattering contour plot, south to north traverse,
February 23, 1974
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.,-' ST. 12
KIRKWOOD ,'' LOUIS
POWER
PLANT
Figure 7. Map of LIDAR traverses, February 25, 1974
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ro
30
25 20
15
POINT OF
INTERSECTION
SOUTH OF POINT
AIRCRAFT GROUND POSITION. KM
15 20
NORTH OF POINT
Figure 8. Iso-scattering contour plot, south to north traverse,
February 25, 1974
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25
20 15 10
WEST OF RIVER
5 I 5 10
MISSISSIPPI
RIVER EAST OF RIVER
AIRCRAFT GROUND POSITION, KM
Figure 9. Iso-scattering contour plot, west to east traverse,
February 25, 1974
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1.4
LU
X
O
UJ
X
900-
800-
700-
600-
500-
400-
300-
200-
SFC
25 30 35
(NEPHELOMETER)
100-
1.0
2.0
3.0
4.0
LIDAR SIGNAL, RELATIVE UNITS
-8
-7
-6
-2
-4 -3
TEMPERATURE,°C
Figure 10. Helicopter profile over Gateway Arch compared with LIDAR
signal, February 25, 1974
14
-1
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U.S EPA Headquarters Library
Mail code 3404T
1200 Pennsylvania Avenue NW
Washington, DC 20460
TABLE 1. SYSTEM PARAMETERS 202-566-0556
PHYSICAL:
Laser - Q-Switched Ruby
o
Frequency: 6943 A
Output Power: 1 joule
Pulse Length: 20 nsec
Firing Rate: ^0.1 HZ
Telescope - 38 cm Fresnel Lens, Aircraft Monoque Construction
Detector - RCA C3100A Photomultiplier
Size - 0.5 m3
Weight - <350 Kg
Power Requirements - 2KW Peak, 600 Watts Standby
OPERATIONAL:
Altitude - Minimum 3,000 m above ground level for Eye Safety
Horizontal Resolution - ^750 m
Vertical Resolution - ^15 m
Sensitivity - 2X Scattering from Clean Air
Signal Rate - 1 pulse every 10 seconds
Output - Strip Chart
Navigation - Visual by Co-Pilot through Window in Cockpit Floor
15
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TABLE 2. TESTING PERIODS
Date
Time/
Start
Location
# of
Laser
Firings
Notes
2/23/74 06:16 S-N Over St. Louis 14
06:41 W-E Over St. Louis 14
11:34 E-W Over St. Louis 34
12:00 N-S Troy, MO to 26
Washington, MO
12:37 S-N Pacifich, MO to 15
O'Fallen, MO
12:48 W-E Over St. Louis 18
2/25/74 21:58 S-N Over St. Louis 25
22:21 W-E Over St. Louis 15
2/26/74 09:19 S-N Over St. Louis 20
09:52 W-E Over St. Louis 23
Attempt to
find dimen-
sions of
the urban
plume
Night flight in
very clear air
Snow on ground
16
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REFERENCES
1. Derr, V. E., Remote Sensing of the Troposphere, U.S. Department of
Commerce, Boulder, CO, 1972.
2. McCormick, M. Patrick, S. Harvey Melfi, Lars E. Olsson, Wesley L. Tuft,
William P. Elliott, and Richard Egami, Mixing-Height Measurement by
LIDAR, Particle Counter, and Rawinsonde in the Willamette Valley,
Oregon, NASA Technical Note, NASA TN D-7103, National Aeronautics and
Space Administration, Washington, D.C., December 1972.
3. McElroy, J. L. and J. F. Clarke, Atmospheric Diffusion During Sunset-
Sunrise Transitional Periods. Paper presented at Symposium on Atmos-
pheric Diffusion and Air Pollution, American Meteorological Society,
Santa Barbara, CA, September 1974.
17
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
1. REPORT NO.
EPA-600/4-76-028
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
AIRBORNE LIDAR RAPS STUDIES, FEBRUARY 1974
5. REPORT DATE
June 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S) "
John A. Eckert, James L. McElroy, Donald H. Bundy,
John L. Guagliardo. and S. H. Melfi
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada .,89114
10. PROGRAM ELEMENT NO.
1AA603
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA-Office of Air, Land and
Water Use
15. SUPPLEMENTARY NOTES
16. ABSTRACT
During February 1974, an airborne downlooking LIDAR system was flown
in support of the Regional Air Pollution Study being conducted by the
U.S. Environmental Protection Agency (EPA) in St. Louis, Missouri. The
LIDAR system was used primarily to measure mixing layer height over the
metropolitan area during the morning and evening transition periods.
The flight plan consisted of south to north and west to east traverses
with horizontal data resolution of 1.5 kilometers and a vertical resolu-
tion of 30 meters. (One traverse over the greater St. Louis area could
be flown in about 10 minutes.) Final data are presented in computer-
generated, iso-scattering curves plotted for altitude versus ground-
distance along the particular traverse.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Lasers
Atmospheric physics
Air pollution
Environmental surveys
Aerosols
Boundary layer
LIDAR
Regional Air Pollution
Study
Mixing height
04A
07D
14D
20E
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)'
UNCLASSIFIED
21. NO. OF PAGES
24
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
•&GPO 691-429-1976
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