Radiative transfer in random inhomogeneous media

Abstract

Radiative transfer in random inhomogeneous media has been considered by a number of authors. The most detailed treatments pertain to radiative transfer in the small-angle scattering approximation. I use a local-perturbation method1 to obtain an equation for the transfer of the mean specific intensity in media in which the small-angle scattering approximation is not valid. My method assumes that the fraction of radiation is scattered or absorbed over a correlation length of the random medium is small compared with the fraction that propagates undisturbed through the same distance. With this assumption my equation for the transfer of the mean specific intensity takes the same form as that of the usual radiative transfer theory, with extinction and scattering coefficients that are determined by both the first- and the second-order statistics of the fluctuating medium. For particular problems the mean specific intensity can be calculated by using the standard numerical techniques that are employed in radiative transfer theory. The local perturbation method that I use can also be applied to the derivation of equations for the propagation of higher-order moments of the specific intensity in random media that do not satisfy the small-angle scattering approximation.