Radar as a coherent imager is physically based on the wave equations that govern the behavior of wave-targets interactions through the process of radiation, transmission, propagation, and reflection/refraction. This chapter briefly introduces the stochastic wave equations at a minimum but sufficient level to serve as fundamentals of radar imaging. Major advances have been made in numerical solutions of Maxwell equations in three-dimensional simulations for rough surface scattering. The chapter describes the governing equations and the calculation of incident fields and scattered fields of a dielectric rough surface with a finite extent. It shows that how the reflected part of the dyadic Green’s function is cast into formulation such that the modification of the numerical coding can be minimized within the framework of the physics-based two-grid method. The chapter examines the imaging performance of space-frequency time-reversal multiple signal classification under the influence of a random medium.