Abstract: A radio frequency emitter transmits pulses in a regular swept beam pattern. As a result of this regular pattern, the angles of transmission of the pulses can be inferred. Intervisibility data of terrain points in a region around an observation point are stored in computer memory. At the observation point, measurements are made of the times of arrival of a plurality of terrain point reflections of a single pulse transmitted by the emitter. These measurements are repeated for a plurality of pulses transmitted by the emitter. In a computer, a comparison is made of the terrain points of reflection calculated from the measured times of arrival for assumed emitter locations with the stored intervisibility data of terrain points.