Flight test evaluation of various terrain referenced navigation techniques for aircraft approach guidance

This paper discusses the evaluation of two sets of terrain referenced navigators (TRN). The first set of TRN systems use radar altimeter measurements, baro-altimeter measurements, and inertial navigation system (INS) measurements, whereas, the second set uses an INS integrated with terrain observations from an Airborne Laser Scanner (ALS). The former set includes techniques such as Terrain Contour Matching (TERCOM), Sandia Inertial Terrain-Aided Navigation (SITAN), and Parallel SITAN. The latter set includes the Terrain Aided Inertial Navigator (TERRAIN), a TRN system that has recently been designed and implemented at Ohio University. The performance of all the aforementioned TRN schemes are evaluated for precision approach and landing using sets of data from two actual flight tests: (a) with NASA Langley's B757 in Eagle-Vail, CO, (b) and with Ohio University's DC-3 in Braxton, WV. The flight test data is unique in the sense that several types of radar altimeter and ALS systems were flown and that terrain databases from various sources are available for these areas. Furthermore, the flight test data include both enroute and approach path segments. The paper addresses various aspects of the TRN systems when used with conventional civil commercial aircraft sensors. These aspects include the sensitivity to the systems to sensor accuracy and operational performance, database resolution.