Abstract

Spatial variations in the polarization properties of multiple scattering have been observed in the lidar backscattering from atmospheric water droplet clouds. To detect these effects, the lidar receivers have been modified to incorporate spatial filters in the focal plane which block singly scattered radiation and transmit muliply backscattered radiation through sectors oriented at five azimuthal angles between 0 and 90° to the direction of the transmitted linear polarization. The parallel and perpendicular polarized components of the lidar multiple scattering have been measured as a function of pulse penetration depth for different cloud formations. The anisotropic distributions observed are found to resemble those previously recorded in our laboratory measurements on clouds of spherical scatterers. In this paper also, results of Mie scattering calculations are summarized which show that the observed polarization anisotropy originates directly from the polarization properties of the single scattering from spherical particles.

© 1985 Optical Society of America

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References

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  1. A. I. Carswell, in Clouds, Their Formation, Optical Properties and Effects, P. V. Hobbs, A. Deepak, Eds. (Academic, New York, 1981), p. 363.
    [CrossRef]
  2. S. R. Pal, A. I. Carswell, “Multiple Scattering in Atmospheric Clouds: Lidar Observations,” Appl. Opt. 15, 1990 (1976).
    [CrossRef] [PubMed]
  3. J. D. Houston, A. I. Carswell, “Four-Component Polarization Measurement of Lidar Atmospheric Scattering,” Appl. Opt. 17, 614 (1978).
    [CrossRef] [PubMed]
  4. K. Sassen, “Air-Truth Lidar Polarization Studies of Orographic Clouds,” J. Appl. Meteorol. 17, 73 (1978).
    [CrossRef]
  5. C. M. R. Platt, N. L. Abshire, G. I. McNice, “Some Micro-physical Properties of Ice Clouds from Lidar Observation of Horizontally Oriented Crystals,” J. Appl. Meteorol. 17, 1220 (1978).
    [CrossRef]
  6. J. S. Ryan, S. R. Pal, A. I. Carswell, “Laser Backscattering from Dense Water-Droplet Clouds,” J. Opt. Soc. Am. 69, 60 (1979).
    [CrossRef]
  7. A. I. Carswell, S. R. Pal, “Polarization Anisotropy in Lidar Multiple Scattering from Clouds,” Appl. Opt. 19, 4123 (1980).
    [CrossRef] [PubMed]
  8. R. L. Cheung, A. Ishimaru, “Transmission, Backscattering, and Depolarization of Waves in Randomly Distributed Spherical Particles,” Appl. Opt. 21, 3792 (1982).
    [CrossRef] [PubMed]

1982 (1)

1980 (1)

1979 (1)

1978 (3)

J. D. Houston, A. I. Carswell, “Four-Component Polarization Measurement of Lidar Atmospheric Scattering,” Appl. Opt. 17, 614 (1978).
[CrossRef] [PubMed]

K. Sassen, “Air-Truth Lidar Polarization Studies of Orographic Clouds,” J. Appl. Meteorol. 17, 73 (1978).
[CrossRef]

C. M. R. Platt, N. L. Abshire, G. I. McNice, “Some Micro-physical Properties of Ice Clouds from Lidar Observation of Horizontally Oriented Crystals,” J. Appl. Meteorol. 17, 1220 (1978).
[CrossRef]

1976 (1)

Abshire, N. L.

C. M. R. Platt, N. L. Abshire, G. I. McNice, “Some Micro-physical Properties of Ice Clouds from Lidar Observation of Horizontally Oriented Crystals,” J. Appl. Meteorol. 17, 1220 (1978).
[CrossRef]

Carswell, A. I.

Cheung, R. L.

Houston, J. D.

Ishimaru, A.

McNice, G. I.

C. M. R. Platt, N. L. Abshire, G. I. McNice, “Some Micro-physical Properties of Ice Clouds from Lidar Observation of Horizontally Oriented Crystals,” J. Appl. Meteorol. 17, 1220 (1978).
[CrossRef]

Pal, S. R.

Platt, C. M. R.

C. M. R. Platt, N. L. Abshire, G. I. McNice, “Some Micro-physical Properties of Ice Clouds from Lidar Observation of Horizontally Oriented Crystals,” J. Appl. Meteorol. 17, 1220 (1978).
[CrossRef]

Ryan, J. S.

Sassen, K.

K. Sassen, “Air-Truth Lidar Polarization Studies of Orographic Clouds,” J. Appl. Meteorol. 17, 73 (1978).
[CrossRef]

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Figures (12)

Fig. 1
Fig. 1

Backscattered radiation from water suspensions of monodisperse polystyrene spheres ranging in diameter from 0.085 to 6.8 μm showing the spatial anisotropy of multiple scattering. The left column was photographed through a crossed polarizer, the right through a parallel polarizer. The photographic exposures are arbitrary; the black dot in the top left photo indicates the size of the single-scattering region (i.e., the laser beam spot) in all cases.

Fig. 2
Fig. 2

Three different spatial filters.

Fig. 3
Fig. 3

Lidar measurements of the multiply scattered signal Pϕ for a cumulus cloud: (a) values obtained with a parallel polarizer; (b) measurements for a crossed polarizer. In each figure Pϕ is shown for each of the five sectors as a function of lidar pulse penetration depth in the cloud.

Fig. 4
Fig. 4

Polar plots of the lidar Pϕ signal from a cumulus cloud: (a) parallel polarized component; (b) perpendicular component. The Pϕ signal shown here is the integrated return from the full cloud depth to provide a signal equivalent to that obtained in the laboratory with a continuous source as shown in Fig. 1.

Fig. 5
Fig. 5

Polar plots of the integrated Pϕ return from a shower cloud. The parallel and perpendicular polarized components are shown in (a) and (b), respectively. The spatially anisotropic nature of the polarized signal is seen, but the features differ substantially from the previous example.

Fig. 6
Fig. 6

Scattering geometry.

Fig. 7
Fig. 7

Calculated variation of I values with azimuth angle ϕ for the 6.8-μm diam spherical scatterer for (a) forward scattering angles and (b) backward scattering angles.

Fig. 8
Fig. 8

As in Fig. 7 but for the 0.5-μm diam scatterer.

Fig. 9
Fig. 9

As in Fig. 7 but for the 0.085-μm diam scatterer.

Fig. 10
Fig. 10

Calculated variation of I values with azimuth angle ϕ for the 6.8-μm diam spherical scatterer for (a) forward scattering angles and (b) backward scattering angles.

Fig. 11
Fig. 11

As in Fig. 10 but for the 0.5-μm diam scatterer.

Fig. 12
Fig. 12

As in Fig. 10 but for the 0.085-μm diam scatterer.

Equations (5)

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E r = S 1 ( θ ) exp ( i k R + i k z ) E o r / i k R ,
E l = S 2 ( θ ) exp ( i k R + i k z ) E o l / i k R ,
S 1 , 2 ( θ ) = i 1 , 2 ( θ ) exp ( i δ 1 , 2 ) .
I = E s x E * s x = [ P 2 ( θ ) 4 π cos θ cos 2 ϕ + P 1 ( θ ) 4 π sin 2 ϕ ] 2 I ° π r 2 Q R 2 ,
I = E s y E * s y = [ P 2 ( θ ) 4 π cos θ cos ϕ sin ϕ P 1 ( θ ) 4 π sin ϕ cos ϕ ] 2 I ° π r 2 Q R 2 ,

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