Abstract

A lidar system that can measure multiple scattering and depolarization in the atmosphere is being used to study the climatic effects of cirrus clouds and to perform other investigations. The lidar system and its novel aspects are described in this paper. The influence of multiple scattering on noise, signal, and SNR is considered. Special receiver field stops incorporated for multiple scattering measurements, use of low voltage to control the photomultiplier tube gain, and a precision power/energy monitor are described. A technique for aligning transmitter and receiver axes and measuring transmitter beamwidth is presented. The multiple-scattered components of backscattered light are determined by inserting a center-blocked field stop to restrict the receiver field of view to the region outside of the diverging transmitted beam. Typical returns with and without the opaque field stop indicate the amplitude of multiple scattering from cirrus clouds and prove the feasibility of this technique. The depolarization ratio δ and backscatter coefficients from an altostratus cloud illustrate the potential of these quantities for the study of cloud structure and phase.

© 1977 Optical Society of America

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References

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  1. C. M. R. Platt, J. Atmos. Sci. 30, 1191 (1973).
    [Crossref]
  2. S. R. Pal, A. I. Carswell, Appl. Opt. 12, 1530 (1973).
    [Crossref] [PubMed]
  3. E. E. Uthe, R. J. Allen, P. B. Russell, Light detection and ranging (Lidar) support for STM-8W and PVM5 reentry operations. Final report contract F04701-74-C-0016, USAF SAMSO/MNNT Norton AFB, San Bernardino, Calif., Stanford Research Institute project 2859 (1974).
  4. C. A. Northend, R. C. Honey, W. E. Evans, Rev. Sci. Instrum. 37, 393 (1966).
    [Crossref]
  5. R. J. Allen, W. E. Evans, Rev. Sci. Instrum. 43, 1422 (1972).
    [Crossref]
  6. E. E. Uthe, R. J. Allen, Opt. and Quantum Electron. 7, 121 (1975).
    [Crossref]
  7. RCA Photomultiplier Manual, PT-61 (RCA, Harrison, N.J., September1970).
  8. C. M. R. Platt, J. Appl. Meterol. 16, 339 (April1977).
    [Crossref]

1977 (1)

C. M. R. Platt, J. Appl. Meterol. 16, 339 (April1977).
[Crossref]

1975 (1)

E. E. Uthe, R. J. Allen, Opt. and Quantum Electron. 7, 121 (1975).
[Crossref]

1973 (2)

1972 (1)

R. J. Allen, W. E. Evans, Rev. Sci. Instrum. 43, 1422 (1972).
[Crossref]

1966 (1)

C. A. Northend, R. C. Honey, W. E. Evans, Rev. Sci. Instrum. 37, 393 (1966).
[Crossref]

Allen, R. J.

E. E. Uthe, R. J. Allen, Opt. and Quantum Electron. 7, 121 (1975).
[Crossref]

R. J. Allen, W. E. Evans, Rev. Sci. Instrum. 43, 1422 (1972).
[Crossref]

E. E. Uthe, R. J. Allen, P. B. Russell, Light detection and ranging (Lidar) support for STM-8W and PVM5 reentry operations. Final report contract F04701-74-C-0016, USAF SAMSO/MNNT Norton AFB, San Bernardino, Calif., Stanford Research Institute project 2859 (1974).

Carswell, A. I.

Evans, W. E.

R. J. Allen, W. E. Evans, Rev. Sci. Instrum. 43, 1422 (1972).
[Crossref]

C. A. Northend, R. C. Honey, W. E. Evans, Rev. Sci. Instrum. 37, 393 (1966).
[Crossref]

Honey, R. C.

C. A. Northend, R. C. Honey, W. E. Evans, Rev. Sci. Instrum. 37, 393 (1966).
[Crossref]

Northend, C. A.

C. A. Northend, R. C. Honey, W. E. Evans, Rev. Sci. Instrum. 37, 393 (1966).
[Crossref]

Pal, S. R.

Platt, C. M. R.

C. M. R. Platt, J. Appl. Meterol. 16, 339 (April1977).
[Crossref]

C. M. R. Platt, J. Atmos. Sci. 30, 1191 (1973).
[Crossref]

Russell, P. B.

E. E. Uthe, R. J. Allen, P. B. Russell, Light detection and ranging (Lidar) support for STM-8W and PVM5 reentry operations. Final report contract F04701-74-C-0016, USAF SAMSO/MNNT Norton AFB, San Bernardino, Calif., Stanford Research Institute project 2859 (1974).

Uthe, E. E.

E. E. Uthe, R. J. Allen, Opt. and Quantum Electron. 7, 121 (1975).
[Crossref]

E. E. Uthe, R. J. Allen, P. B. Russell, Light detection and ranging (Lidar) support for STM-8W and PVM5 reentry operations. Final report contract F04701-74-C-0016, USAF SAMSO/MNNT Norton AFB, San Bernardino, Calif., Stanford Research Institute project 2859 (1974).

Appl. Opt. (1)

J. Appl. Meterol. (1)

C. M. R. Platt, J. Appl. Meterol. 16, 339 (April1977).
[Crossref]

J. Atmos. Sci. (1)

C. M. R. Platt, J. Atmos. Sci. 30, 1191 (1973).
[Crossref]

Opt. and Quantum Electron. (1)

E. E. Uthe, R. J. Allen, Opt. and Quantum Electron. 7, 121 (1975).
[Crossref]

Rev. Sci. Instrum. (2)

C. A. Northend, R. C. Honey, W. E. Evans, Rev. Sci. Instrum. 37, 393 (1966).
[Crossref]

R. J. Allen, W. E. Evans, Rev. Sci. Instrum. 43, 1422 (1972).
[Crossref]

Other (2)

E. E. Uthe, R. J. Allen, P. B. Russell, Light detection and ranging (Lidar) support for STM-8W and PVM5 reentry operations. Final report contract F04701-74-C-0016, USAF SAMSO/MNNT Norton AFB, San Bernardino, Calif., Stanford Research Institute project 2859 (1974).

RCA Photomultiplier Manual, PT-61 (RCA, Harrison, N.J., September1970).

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Figures (7)

Fig. 1
Fig. 1

Shot noise component of PMT anode current resulting from background radiation plotted for various clear-aperture disks (for mean clear sky background = 10−2 w · m−2 sr−1 nm−1, RCA 7265 PMT, 1-nm bandwidth filter, and polarizing filter removed).

Fig. 2
Fig. 2

Examples of specially designed blocked-aperture field stops: (a) blocked-aperture field stop etched on Mylar rubylith sheet and reduced four times (example shown is 1.2 mrad); (b) clear-aperture field-stop metal disk (example shown is 6 mrad); (c) blocking aperture overlaid with clear-aperture disk.

Fig. 3
Fig. 3

The signal return (in arbitrary units) measured using a 1-mrad clear-aperture field stop as the laser pulse image is moved laterally across the telescope focal plane.

Fig. 4
Fig. 4

The relative signal return with blocked-aperture field stops of various sizes interposed in the center of the telescope focal plane (10-mrad clear aperture field stop).

Fig. 5
Fig. 5

Multiple-scattered return from a cirrus cloud when using a 2-mrad blocked-aperture field stop (2-MHz electronic filter and 10-mrad clear aperture field stop).

Fig. 6
Fig. 6

Return from a cirrus cloud without using a blocked-aperture field stop (2-MHz electronic filter and 10-mrad clear-aperture field stop).

Fig. 7
Fig. 7

Backscatter coefficient from mixed-phase (ice and water) altostratus clouds together with the depolarization ratio (after Platt8 (data collected on 9 August 1975; 1518 local apparent time; Aspendale, Australia).

Equations (15)

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Ω B = A b / R 2 = π ( θ T / 2 ) 2
Ω R Ω B ,
N r = Ω R B λ A R [ t N ( D ) t p ( ϕ ) t o ] Δ λ             ( blocking field stop removed )
N i = ( Ω R - Ω B ) B λ A R [ t N ( D ) t p ( ϕ ) t o ] Δ λ             ( blocking field stop inserted ) ,
I b = μ q N
i b = μ ( 2 e q N Δ f ) 1 / 2 ,
I s = μ q S
i s = μ ( 2 e q S Δ f ) 1 / 2 .
i dc = μ ( 2 e I d c Δ f ) 1 / 2 .
S m = S T - S s
S m = t T P o τ c A R 8 π R 2 [ t N ( D ) t p ( ϕ ) t o ] B ( π , R ) { exp [ - 0 R 2 η ( Ω R , Ω B , R ) σ v ( R ) d R ] - exp [ - 0 R 2 σ v ( R ) d R ] } ,
η 1             ( below the cloud )
σ v = σ a + σ R             ( below the cloud ) ,
η < 1             ( within the cloud )
σ v = σ c             ( within the cloud ) ,

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