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J. W. Hovenier

Abstract

In this paper we discuss symmetry properties of the matrices describing the reflection and transmission of polarized radiation by a slab of randomly oriented particles. A complete set of such symmetry relations valid in the common case in which there is no birefringence or dichroism is given. The derivation proceeds via 1) the symmetry properties of the phase matrix describing the scattering in a volume element and 2) the symmetry properties of the reflection and transmission matrices based on single scattering only. Birefringence and dichroism may occur if the particles do not have a plane of symmetry. The study of symmetry relations for this case is not carried beyond the stage of the phase matrix.

Possible applications and some errors in the literature are pointed out.

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James E. Hansen and J. W. Hovenier

Abstract

The linear polarization of sunlight reflected by Venus is analyzed by comparing observations with extensive multiple scattering computations. The analysis establishes that Venus is veiled by a cloud or haze layer of spherical particles. The refractive index of the particles is 1.44±0.015 at λ=0.55 μm with a normal dispersion, the refractive index decreasing from 1.46±0.015 at λ=0.365 μm to 1.43±0.015 at λ=0.99 μm. The cloud particles have a narrow size distribution with a mean radius of ∼1 μm; specifically, the effective radius of the size distribution is 1.05±0.10 μm and the effective variance is 0.07±0.02. The particles exist at a high level in the atmosphere, with the optical thickness unity occurring where the pressure is about 50 mb.

The particle properties deduced from the polarization eliminate all but one of the cloud compositions which have been proposed for Venue. A concentrated solution of sulfuric acid (H2SO4-H2O) provides good agreement with the polarization data.

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