INTENSITY OF DIFFUSE-RADIATION IN PARTICULATE MEDIA

A method for calculating the angular and optical depth dependencies of diffuse radiation in light scattering and absorbing particulate media is established. From the Lorenz-Mie theory, the coefficients involved in the expansion of the single particle phase function in terms of Le gendre polynomials are obtained. Then the angular dependence of diffus e radiation is described by means of generalized phase functions, corr esponding to the different scattering orders. The optical depth depend ence is given in terms of weighting factors, which depend on average p ath-length parameters and forward-scattering ratios of the different s cattering orders. Intensity patterns are obtained for different partic le sizes, concentrations, and relative refractive indices, and the beh avior of the forward and backward diffuse intensities in terms of opti cal depth is displayed. Comparisons with the forward-multiple-scatteri ng theory of Hartel are carried out. A generalization of the Beer-Lamb ert law in the case of light-scattering materials is obtained from the present approach, which is derived from the radiative transfer equati on. (C) 1997 Optical Society of America.