Coherence equations governing propagation through random media

In this paper we consider the equations governing the second‐ and fourth‐order coherence functions in random media. We first treat radiation propagating in a homogeneous and isotropic random medium in the limit of small wavelengths. We summarize the solutions that are available and report on some recent unpublished work. We next show how these equations may be generalized to include a nonhomogeneous background and the effects of anisotropy under acoustic conditions. The utility of the equations for considering free‐space propagation is also discussed.