As land-mobile satellite systems and radio-determination systems get more importance in the global telecommunications scenario, it becomes even more necessary to understand the radio-propagation environment: its behavior and the inter-relationship between its several aspects and physical parameters. Due to the communications devices characteristics used in these systems, such as low-power transmitters and low/medium gain antennas, such systems operate with relatively low fade margins. The technical literature describes a simulation technique to estimate fade margins in various types of environments, based on the processing of photographs acquired by digital cameras utilizing fisheye lenses. In this dissertation, an alternate methodology is presented. It is proposed that the original database of photographs be substituted by digital elevation models combined with building databases and a vegetation model. The computer simulation structure used to process and analyzes these databases, the input simulation data, and an orbital dynamics model used to update the satellite positions are also described. Finally, the obtained simulation results are presented and analyzed. It also discusses the influence of several factors which characterize different urban regions and non geostationary orbit satellite networks in the obtained results.