Heli/SITAN: a terrain referenced navigation algorithm for helicopters

Heli/SITAN is a terrain referenced navigation algorithm that utilizes radar altimeter ground clearance measurements in combination with a conventional navigation system and a stored digital terrain elevation map to estimate a helicopter´s position accurately. Multiple model adaptive estimation techniques are used, and a bank of single-state Kalman filters is used to ensure that reliable position estimates are obtained even in the face of large initial position errors. A real-time implementation of the algorithm was tested aboard a US Army UH-1 helicopter equipped with a Singer-Kearfott Doppler velocity sensor and a Litton LR-80 strapdown attitude and heading reference system (AHRS). The median radial error of the position fixes provided in real time by this implementation was less than 50 m for a variety of mission profiles. Although Heli/SITAN was demonstrated on a helicopter equipped with a Doppler aided AHRS, the extension to other types of aircraft and navigation systems is straightforward