terrainreferenced

Terrain-referenced navigation is a method of determining a vehicle's position by matching observations of the surrounding landscape to a stored digital terrain model. The system uses sensors such as radar mapping equipment, radar altimeters, or LIDAR to measure terrain features and elevation, and a processor to correlate these observations with a terrain database, usually in combination with an inertial navigation system.

Operation involves measuring the terrain profile along the vehicle’s path, converting it into a feature representation, and performing a correlation with the terrain model to derive a position fix. This approach is valuable in GNSS-denied environments because it provides a position reference independent of satellite signals and can enhance mission robustness and safety.

Typical components include a digital terrain database, terrain observation sensors, a correlator or matching processor, and an inertial navigation system integrated through a navigation filter.

Applications have been broad in aviation, including military aircraft and helicopters operating in contested airspace, with TERPROM-type systems historically used to improve navigation accuracy and situational awareness. The concept has also appeared in missile guidance as a variant known as terrain contour matching, though that is a related but distinct approach.

Advantages include resistance to jamming and spoofing, wide-area coverage, and the ability to operate where GNSS is degraded. Limitations include dependence on terrain variability, reduced performance in flat or repetitive terrain, the need for up-to-date terrain data, and the potential for errors due to inaccuracies in the terrain database or sensor calibration.

Development began in the mid-20th century and has evolved with digital terrain models and enhanced correlators; it remains a complementary or alternative navigation solution in modern avionics.