A critical issue for designers of communication systems is the characterization of the communication channel. The free-space propagation model does not adequately predict the mean path loss in space-to-ground communication systems. Traditional methods for predicting the effect of terrain impacting the path of propagating signals focus on statistical or empirical models, which can not always be extrapolated to model prevailing physical conditions. This study focuses instead on the development and application of knife-edge and rounded obstacle terrain models. The models are based on the geometric theory of diffraction and predict the attenuation affects due to diffraction caused by signal propagation over terrain.