The Twersky procedure is used to derive the vector Foldy-LaxTwersky integral equation (Dyson equation) for the coherent field in a random distribution of particles. The above equation is applied to ice depolarization and rain attenuation and depolarization. Twersky's procedure is then extended in order to derive a vector-valued Dyson equation and a tensor-valued two-frequency BetheSaltpeter equation for waves propagating in a distribution of spatially pair correlated absorptive scatterers. From these equations a systematic transition is made to a two-frequency radiative transfer equation suitable forpusled scalar waves in the presence of a tenuous distribution of absorptive isotropic discrete scatterers with pair correlations. / Ph. D.