C. T. Field is with the Department of Electrical Engineering, U.S. Naval Academy, Annapolis, Maryland 21402. His e-mail address is field@nadn.navy.mil.
P. S. Millar is with the Laser Remote Sensing Branch, NASA Goddard Space Light Center, MS 924, Greenbelt, Maryland 20771.
We develop a general model of a laser remote-sensing system for
search and rescue using targets marked with fluorescent dye. The
dye fluoresces at a longer peak wavelength than the incident radiation,
enabling a dye-covered target to be distinguished from the unshifted
ground echo by the search system. The principal result is a simple
expression derived for the average laser power required to search at a
particular rate given a required ground energy density. A similar
expression is applicable to imaging lidar systems. The example
system shown indicates that active probing for lost planes may be
practical.
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Computed from flux values in Ref.
12. System parameters are from Table 1. The
lunar noise counts are all less than 0.2 and Poisson statistics must be
used.
Pump energy density that is needed to
generate the minimum required target emission of 4.2 ×
1012 photons within the receiver bandwidth versus target
fluorescence yield for four target areas. Pump and emission
wavelengths are 532 and 600 nm, respectively.
Table 5
Average Optical Energy Requirements versus Search
Conditions
Energy Density EG (µJ/cm2)
CF (%)
Search Rate Ss (km2/h)
Average Power Pav
10 Shots/s
1000 shots/s
Spot Area (m2)
Pulse Energy
Spot Area (m2)
Pulse Energy
3000
100
180
1.5 MW
5000
210 kJ
50
2.1 kJ
3000
25
10
21 kW
70
3.0 kJ
0.8
30 J
1
50
90
125 W
1200
1.8 J
12
18 mJ
0.1
50
90
13 W
1200
1.8 J
12
18 mJ
0.005
100
180
2.5 W
5000
360 mJ
50
3.6 mJ
0.0016
100
180
0.8 W
5000
115 mJ
50
1.2 mJ
Tables (5)
Table 1
Assumed System Parameters
Description
Symbol
Value
Search speed
Ss
180 km2/h
Ground coverage
CF
100%
Plane altitude
Rp
1 km
Scan angle
θmax
±30 deg
Plane speed
Vp
160 km/h
(100 mi/h)
Pump wavelength
λp
532 nm
Pulse rate
f
10 kHz
Atmospheric transmission (one way)
ηatm
70%
Ground albedo
ρ
50%
Target conversion
ηBW
10%
Receiver wavelength
λr
600 nm
Receiver bandwidth
Δλr
10 nm
Receiver radius
Rr
10 cm
Receiver efficiency
ηD
10%
Receiver field of view
θfov
3 mrad
Observation window
Δtr
100 ns
False-alarm probability
PF
10-9
Miss probability
PM
10-9
Table 2
Derived System Parameters using the Values in Table 1
Computed from flux values in Ref.
12. System parameters are from Table 1. The
lunar noise counts are all less than 0.2 and Poisson statistics must be
used.
Pump energy density that is needed to
generate the minimum required target emission of 4.2 ×
1012 photons within the receiver bandwidth versus target
fluorescence yield for four target areas. Pump and emission
wavelengths are 532 and 600 nm, respectively.
Table 5
Average Optical Energy Requirements versus Search
Conditions