Abstract

The scattering of waves by particles of moderate size is nonisotropic. In this paper, the backscattering enhancement of scattering of waves by nonisotropic scatterers is studied. Multiple-scattering effects are included by examining the summation of all the ladder terms and all the cyclical terms. It is shown that if the observation angle is in the neighborhood of the backscattering direction, then both summations can be related to the unidirectional point-source Green’s function of the transport equation. For the case of small albedo or small optical thickness, the second-order theory is applied to calculate the Green’s function. The angular width of backscattering enhancement in this case is of the order of the coherent wave attenuation rate divided by the wave number. For the case of a large albedo and a large optical thickness, the diffusion approximation is used to calculate the Green’s function. For this case, the angular width is of the order of the transport rate divided by the wave number. The transport rate is equal to the product of the coherent wave-attenuation rate and 1 minus the mean cosine of the scattering angle. Hence the predicted angular width is substantially smaller for particles with dominant forward scattering and is shown to be in good agreement with experimental observations.

© 1988 Optical Society of America

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