A 3D spatial integrity monitor for terrain databases

Advanced cockpit display systems are the topic of active research to overcome the problems caused by limited visibility and to improve aircraft safety and airport operations, in general. The National Aeronautics and Space Administration's (NASA) Aviation Safety and Security Program (AvSSP) is developing Synthetic Vision Systems (SVS) to improve a pilot's situational awareness. SVS provide a pilot with either a Heads-Up Display (HUD) or a Heads-Down Display (HDD) containing information about aircraft state, guidance, obstacles and the terrain features over which the aircraft is flying. Out of these, the terrain feature information is extracted on-board from terrain databases. For applications that improve flight safety, it is imperative that the terrain database conforms to a high level of integrity. Otherwise, instead of preventing accidents, the terrain database would be the cause of more. To ensure that the terrain elevation data used for the SVS display imagery conforms to a required reliability, it may be necessary to include an integrity monitor function to the terrain database server. This paper builds upon previously proposed concepts and discusses the concept of a three-dimensional spatial integrity monitor (in the vertical and the two-dimensional horizontal domains) for detecting bias errors. The lower the magnitude of the integrity monitor's minimum detectable bias, the better the integrity monitor. A Kalman filter is designed to make the integrity monitor sensitive to lower magnitudes of bias. The concepts developed for the spatial integrity monitor are extended to a terrain referenced navigation scheme called the spatial position estimator. The performance of the proposed integrity monitor and position estimator 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.