Modified radiative transfer theory in second‐order backscattering coefficients of a two‐layer random medium

The modified radiative transfer theory is used to obtain the backscattering coefficients of a two‐layer random medium. Since exact solutions to the MRT equations are not available certain approximations are used. First, a first‐order approximation is made to obtain the backscattering coefficients. In an attempt to investigate the appropriateness of the first‐order approximation, higher‐order solutions are obtained. It is observed that the second‐order solution is important because it is the primary source of depolarization (cross‐polarized backscatter); besides it also helps one to estimate the error involved in settling for a first‐order approximation. Hence the second‐order backscattering coefficients are calculated and cast in a form suitable for physical interpretation. It is noticed that certain “phase” terms are absent. After exploring the reasons for this, it is suggested that the present MRT theory be further modified to accommodate these terms. Finally, with the help of numerical examples, characteristics of the second‐order solutions are studied by comparing them with the corresponding Born results and also with the first‐order solutions.