MULTIPLE-SCATTERING FROM CHEBYSHEV PARTICLES - MONTE-CARLO SIMULATIONS FOR BACKSCATTERING IN LIDAR GEOMETRY

Lidar measurements are often interpreted on the basis of two fundament al assumptions: absence of multiple scattering and sphericity of the p articles that make up the diffusing medium. There are situations in wh ich neither holds true. We focus our interest on multiply-scattered re turns from homogeneous layers of monodisperse, randomly oriented, axis ymmetric nonspherical particles. T-2 Chebyshev particles have been cho sen and their single-scattering properties have been reviewed. A Monte Carlo procedure has been employed to calculate the backscattered sign al for several fields of view. Comparisons with the case of scattering from equivalent (equal-volume) spheres have been carried out (narrow polydispersions have been used to smooth the phase functions' oscillat ions). Our numerical effort highlights a considerable variability in t he intensity of the multiply-scattered signal, which is a consequence of the strong dependence of the backscattering cross section on deform ation of the particles. Even more striking effects have been noted for depolarization; peculiar behavior was observed at moderate optical de pths when particles characterized by a large backscattering depolariza tion ratio were employed in our simulations. The sensitivity of depola rization to even small departures from sphericity, in spite of random orientation of the particles, has been confirmed. The results obtained with the Monte Carlo codes have been successfully checked with an ana lytical formula for double scattering. (C) 1996 Optical Society of Ame rica.