Position determination and message transfer system employing satellites and stored terrain map

摘要

A radio position determation and message transfer system is implemented using a pair of satellites in geostationary orbit for replaying interrogation and replay signals between a ground station and a user-carried transceiver. The user portion is calculated based on the arrival times of replay signals received at the ground station via the two satellites, the known transmission time of the interrogation signal from the ground station, and the user's elevation on the surface of the earth. The elevation is derived from a stored terrain map providing local terrain elevations at a plurality of points of the earth's surface. The stored terrain map allows accurate position fixed to be obtained for surface users regardless of the deviation of the local terrain from the spherical or ellipsoidal model of the earth's surface.