Fast prediction of scattering in mountainous terrain using commonly visible surfaces

This paper discusses a computer program for deterministic prediction of radio wave scattering in hilly and mountainous terrain using a DTED terrain database. A fast and accurate visibility algorithm with a linear computational complexity and little RAM requirement is invented to find the terrain elements that are commonly visible to both ends of the communication links. Comparing with the vertical plane contribution predicted by the TIREM model, we find that in about 1/3 of the cases the terrain scattering contribution is more significant than the vertical plane contribution in a typical mountainous terrain. We also find milliseconds computation times per link can be achieved on a personal computer for large maps by pre-computing macro-visibility. Computation that finds visibility on-the-fly takes 6 times longer.