The purpose of this interim report is to give an account of the progress in the development of models for the interaction between a target object and the surrounding terrain. The radar cross section at 10 GHz has been studied for the simple type case of a rectangular plate leaning with variable inclination on a rough ground surface. The interaction has been modelled in two different ways. The first method estimates the mean interaction. The second approach is to do coherent calculations for a model generated with a stochastically faceted ground surface. The two methods are compared for three different inclinations. These methods, as well as the intermediate level incoherent modelling with stochastic variations are discussed. Requirements on software for coherent calculations on stochastic models are suggested, and conclusions on limitations in the applicable angular range are given. Further conclusions can only be drawn after measurements in a later stage of this project.