Abstract

A parametric study of a 10.6-μ laser radar using heterodyne detection is presented. Returns from various noncooperative targets have been obtained at ranges of up to 8 km. The radar equipment uses an offset local oscillator frequency in order to avoid homodyne operation. Measurements of signal-to-noise ratio over a 1.06-km range show that the system is within a factor of 4 of quantum-limited operation. For visibility ranging from 305 m to 120 km the scattering coefficient is found to range from 1.05 × 10−8 m−1 to 4.21 × 10−7 m−1. The depolarization of returns from targets and from atmospheric aerosols is found to be less than ≈20% for targets and near zero for aerosols. Both atmospheric and target scintillation have been studied, with the conclusion that target-induced scintillation is generally larger. Atmospheric scintillation is found to be much less severe than for visible laser wavelengths. Finally, measurements of the frequency broadening introduced by the scanner are presented. Good agreement with a simple theoretical model involving Doppler shift from the scanning mirror is obtained.

© 1972 Optical Society of America

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References

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  1. J. H. McCoy, D. B. Rensch, R. K. Long, Appl. Opt. 8, 1471 (1969).
    [CrossRef] [PubMed]
  2. H. A. Bostick, IEEE J. Quantum Electron. QE-3, 232 (1967).
    [CrossRef]
  3. M. C. Teich, R. J. Keyes, R. H. Kingston, Appl. Phys. Lett. 9, 357 (1966).
    [CrossRef]
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    [CrossRef]
  5. A. M. Robinson, D. C. Johnson, IEEE J. Quantum Electron. QE-6, 590 (1970).
    [CrossRef]
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    [CrossRef]
  7. Max Bair, University of Michigan, Willow Run Laboratory, private communication.
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    [CrossRef] [PubMed]

1970

A. M. Robinson, D. C. Johnson, IEEE J. Quantum Electron. QE-6, 590 (1970).
[CrossRef]

W. T. Cathey, C. L. Hayes, W. C. Davis, V. F. Pizzurro, Appl. Opt. 9, 701 (1970).
[CrossRef] [PubMed]

1969

1967

H. A. Bostick, IEEE J. Quantum Electron. QE-3, 232 (1967).
[CrossRef]

C. J. Buszek, G. S. Picus, Appl. Phys. Lett. 11, 125 (1967).
[CrossRef]

1966

M. C. Teich, R. J. Keyes, R. H. Kingston, Appl. Phys. Lett. 9, 357 (1966).
[CrossRef]

Bair, Max

Max Bair, University of Michigan, Willow Run Laboratory, private communication.

Bostick, H. A.

H. A. Bostick, IEEE J. Quantum Electron. QE-3, 232 (1967).
[CrossRef]

Buszek, C. J.

C. J. Buszek, G. S. Picus, Appl. Phys. Lett. 11, 125 (1967).
[CrossRef]

Cathey, W. T.

Davis, W. C.

Hayes, C. L.

Johnson, D. C.

A. M. Robinson, D. C. Johnson, IEEE J. Quantum Electron. QE-6, 590 (1970).
[CrossRef]

Keyes, R. J.

M. C. Teich, R. J. Keyes, R. H. Kingston, Appl. Phys. Lett. 9, 357 (1966).
[CrossRef]

Kingston, R. H.

M. C. Teich, R. J. Keyes, R. H. Kingston, Appl. Phys. Lett. 9, 357 (1966).
[CrossRef]

Long, R. K.

McCoy, J. H.

Picus, G. S.

C. J. Buszek, G. S. Picus, Appl. Phys. Lett. 11, 125 (1967).
[CrossRef]

Pizzurro, V. F.

Rensch, D. B.

Robinson, A. M.

A. M. Robinson, D. C. Johnson, IEEE J. Quantum Electron. QE-6, 590 (1970).
[CrossRef]

Teich, M. C.

M. C. Teich, R. J. Keyes, R. H. Kingston, Appl. Phys. Lett. 9, 357 (1966).
[CrossRef]

M. C. Teich, in Semiconductors and SemimetalsR. K. Willardson, A. C. Beer, Eds. (Academic, New York, 1970), Vol. 5, p. 361.
[CrossRef]

Appl. Opt.

Appl. Phys. Lett.

M. C. Teich, R. J. Keyes, R. H. Kingston, Appl. Phys. Lett. 9, 357 (1966).
[CrossRef]

C. J. Buszek, G. S. Picus, Appl. Phys. Lett. 11, 125 (1967).
[CrossRef]

IEEE J. Quantum Electron.

A. M. Robinson, D. C. Johnson, IEEE J. Quantum Electron. QE-6, 590 (1970).
[CrossRef]

H. A. Bostick, IEEE J. Quantum Electron. QE-3, 232 (1967).
[CrossRef]

Other

M. C. Teich, in Semiconductors and SemimetalsR. K. Willardson, A. C. Beer, Eds. (Academic, New York, 1970), Vol. 5, p. 361.
[CrossRef]

Max Bair, University of Michigan, Willow Run Laboratory, private communication.

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Figures (12)

Fig. 1
Fig. 1

Schematic diagram of optical and electronic configuration.

Fig. 2
Fig. 2

Spectral analysis of servocontrolled beat between local oscillator and transmitter lasers. Horizontal scale, 2 kHz/cm; vertical scale, linear; sample time, ≈0.1 sec.

Fig. 3
Fig. 3

Measured current vs local oscillator power for Cu:Ge detector. Un coated Irtran IV window; power plotted is the power incident on the dewar. Parameter (V) is the voltage across the detector.

Fig. 4
Fig. 4

Scanning mirror configuration.

Fig. 5
Fig. 5

Frequency spectrum resulting from scanner broadening. Parameters = 2θ B 0 = 55 mrad, scan rate = 40 Hz. Analyzer scan rate = 3 sweeps/sec, 10 scans per photograph. Vertical scale, linear; horizontal scale, 10 kHz/cm.

Fig. 6
Fig. 6

Scanner broadening vs full-scan angle.

Fig. 7
Fig. 7

Configuration for analysis of backscatter signal.

Fig. 8
Fig. 8

Plot of (16π/D2P0s)dp/dr vs range. The following parameters were used: α = 0.33 × 10−3 rad, D = 5.8 cm, Δ = 8.3 cm.

Fig. 9
Fig. 9

Frequency spectrum of backscatter return for two cases. Upper: clear air, visibility greater than 120 km; Lower: fog and smog, visibility 305–610 m. Pointing direction was just above the horizon. Vertical scale: linear; upper, 0.17 mV (rms)/cm; lower, 0.453 mV (rms)/cm. Horizontal scale: 100 kHz per cm, centered at 4.5 MHz.

Fig. 10
Fig. 10

Target scintillation. For each picture the horizontal scale is 0.5 sec/cm and the vertical scale is 0.5 V/cm. Range, 1.06 km. Carrier frequency is the 4.5-MHz laser offset frequency. Upper: beam centered on stable diffuse target. Middle: beam at edge of stable diffuse target. Lower: beam centered on 60-cm × 60-cm wind-blown aluminum plate.

Fig. 11
Fig. 11

Return from diffuse target illustrating atmospheric scintillation. Range, 1.06 km; sample time, 0.1 sec. Upper: 2:20 p.m. Lower: 9:30 p.m.

Fig. 12
Fig. 12

Diurnal variation of atmospheric scintillation.

Tables (2)

Tables Icon

Table I Measured Scattering Coefficients

Tables Icon

Table II Depolarization for Various Targets Relative to Horizontal Transmitter and Receiver Polarization

Equations (16)

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( S / N ) p = η P a / 2 h ν B .
P a = ( R P t T a 2 d r 2 T r / 4 r 2 ) ( E H / E T ) 2 ,
P t = transmitted power = 21.5 W ,
( S / N ) p = 4.98 × 10 3 .
( S / N ) p = 1.23 × 10 3 .
θ m = θ 0 + θ m 0 sin ω t .
υ = r ( d θ m / d t ) = r θ m 0 ω cos ω t
υ = r cos θ m θ m 0 ω cos ω t = d θ m 0 ω cos ω t .
ν r = 2 υ / λ = 2 d θ m 0 ω cos ω t / λ ,
( ν r 2 ) 1 2 = 2 d θ m 0 ω / λ .
Δ ν B = 4 ( ν r 2 ) 1 2 = 4 2 d θ m 0 ω / λ .
Δ ν B = 4 ( ν d 2 ) 1 2 = 2 ( D / λ ) ω θ B 0 .
Δ ν L 10 kHz ( FWB ) , 7 kHz ( FWHM ) ,
P s = D 2 P 0 s 16 π ( Δ D ) / α θ sin θ r 2 e 2 ( s + a ) r d r ,
I = ( Δ D ) / α ( θ sin θ r 2 ) d r .
s = 16 π P s / D 2 P 0 I .

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