Improved downward-looking terrain database integrity monitor and terrain navigation

Terrain database integrity monitors and terrain referenced navigation systems are both based on performing a comparison between stored terrain elevation data and data obtained from airborne sensors such as radar altimeters, inertial measurement units (IMUs), Global Positioning System (GPS) receivers etc. The concept of consistency checking as used for the integrity monitor function originated from terrain referenced navigation systems. This paper discusses the extension to a previously proposed method of improving the performance of a spatial integrity monitor for terrain elevation databases. Furthermore, this paper discusses an improvement of the terrain-referenced aircraft position estimation for aircraft navigation using only the information from downward-looking sensors, GPS and the terrain databases, and not the information from the IMU. Horizontal failures have been characterized based on the sensed terrain information. Kalman filter methods have been designed to achieve the integrity monitor and terrain navigation performance improvements. The performance of the proposed position estimator and integrity monitor is evaluated using flight test data from NASA's flight trials at Eagle/Vail (EGE), CO and Ohio University's flight trials at Albany (KUNI), OH, Asheville (AVL), NC, and Juneau (JNU), AK.