Extension of the geometric optics approximation to the scattering from rough layers

The geometric optics approximation is based on the Kirchhoff-tangent plane approximation (KA), which assumes that each point of the rough surface can be considered as locally flat. Here, the extension of the KA to the case of rough layers for calculating the scattered field is presented, for either flat or rough lower surfaces. Then, for fast computation of the normalized radar cross section (NRCS), KA is reduced in the high-frequency limit to the geometric optics (GO) approximation, by using the method of stationary phase. Last, numerical results are presented by comparison with a reference numerical method to validate the asymptotic GO model.