Application of Spectral Estimation Techniques in Terrain Database Integrity Monitors and Terrain Navigation Systems

A. Vadlamani, M. Uijt de Haag

Abstract:	The principle behind the operation of both terrain database integrity monitors and terrain navigation systems is based on performing a comparison between stored terrain data and data obtained from sensors such as radar altimeters, inertial measurement units (IMUs), Global Positioning System receivers, weather radars, laser range scanners, etc. Spectral estimation techniques could be used to improve the performance of both applications. Terrain elevation database integrity monitors are part of Synthetic Vision Systems (SVS). SVS is an advanced display technology that gives a virtual depiction of the terrain as viewed "from the cockpit". The primary source of these displays is a Digital Elevation Model (DEM) of the terrain. When using the displays for functions other than advisory, it may be necessary to include a DEM integrity monitor that would alert the pilot when the display does not conform to the real world. DEM integrity monitors using forward-looking or downward-looking sensor information like a radar altimeter and GPS inputs have been proposed in the past. The function of the terrain database's integrity monitor is to generate an alarm when it finds inconsistencies between the sensed terrain profile and the DEM terrain profile in real-time. In terrain navigation, external sensors are integrated with terrain databases to obtain position and/or velocity estimates that will enable navigation of the user. Examples are Terrain Contour Matching (TERCOM) and the Sandia Inertial Terrain-Aided Navigation (SITAN). Although terrain navigation systems and integrity monitors have two different functions, both are based on a similar principle: evaluate the consistency between synthesized and stored terrain data. This paper introduces the application of spectral estimation techniques as one of the methods to improve the sensitivity of the downward-looking integrity monitor to horizontal failures. The consistency metrics are transformed to domains such as the frequency and correlation domains and evaluated. In terrain navigation, spectral estimation techniques and frequency domain estimators can augment or replace the traditional Kalman filtering techniques. One method that is being proposed is an autocorrelation function (ACF) estimator; another method is the application of the Maximum Entropy Spectral Estimator (MESE). Both methods are compared to classical statistical integrity monitors. The performance of the proposed position estimators and integrity monitors is evaluated using flight test data from NASA's flight trials at Eagle/Vail (EGE), Colorado with application to autonomous navigation.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	2389 - 2398
Cite this article:	Vadlamani, A., de Haag, M. Uijt, "Application of Spectral Estimation Techniques in Terrain Database Integrity Monitors and Terrain Navigation Systems," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 2389-2398.
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