A passive navigation system for an airborne platform includes an on-board computer
having a database that contains preprogrammed information regarding pre-existing
ground-based signal emitters (e.g. cell-phone, television and radio broadcast transmitters).
For each emitter, the database includes the geolocation of the emitter and identifying
signal characteristic(s) of each emitter's signal such as frequency, bandwidth
and strength. An antenna array and digital receiver cooperate with the computer
on the platform to passively receive signals from the emitters and determine a
direction of arrival (DOA) for selected signals. The computer also extracts identifying
signal characteristic(s) from selected received signals and matches them against
the database information to ascertain the geolocation of the emitter that corresponds
to the received signal. The platform location is then calculated from the DOA(s)
and emitter geolocations using a triangulation-type algorithm. Also, preprogrammed
site-specific terrain scattering information can be compared to observed scattered
signals to enhance system accuracy.
