Design of a Hybrid and Flexible Height Reference System for Flight Inspection

David Gondy and Jörg F. Wagner

Abstract:	The calibration of aeronautical navigation facilities has high demands with respect to accuracy, update rate, and availability of the reference position of the flight inspection aircraft. These requirements cannot be fulfilled by a stand-alone GPS solution. Thus, complementary sensors have to be added: For example, existing equipment use INS, laser trackers, barometers, radio altimeters or laser altimeters for an accurate positioning. Additionally and in order to reach a better accuracy, the position reference is usually calculated in post-processing immediately at the end of the calibration based on the recorded sensor data. The object of the system described here is to provide in post-processing a height reference that complies with the following requirements: 1. Integrating inertial as well as ADC (Air Data Computer) data and alternatively GPS, differential (DGPS) or phase-differential (P-DGPS) data. 2. Flexible integration/removal of laser tracker, radio and laser altimeter sensors in the system. 3. Determination of the accuracy level of the height reference. 4. High availability and integrity of the height reference. 5. Capability of reaching an accuracy compatible with the calibration of different aeronautical navigation facilities (ILS Cat III, Precision Approach Radar, enroute nav-aid) by using predefined combinations of sensors. Inertial, pressure and laser tracker measurements are used to improve the data rate and the dynamic behavior of a stand-alone GPS solution. Moreover, radio and laser altimeters can be used to enhance the accuracy. Of course, both devices are only useful during segments of flights above well-known terrain profiles (such as near runway thresholds). The challenge of using the very accurate radio and laser altimeter measurements is in the fact that they are typically available only at the end of a calibration approach and that they should nevertheless improve the accuracy of the height for the complete calibration procedure. The issue is solved by the use of a data smoother that provides the data fusion and the height estimate. First results show that the accuracy requirements are reached for ILS Cat III as well as for Precision Approach Radar (PAR) and en-route calibration.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2388 - 2395
Cite this article:	Gondy, David, Wagner, Jörg F., "Design of a Hybrid and Flexible Height Reference System for Flight Inspection," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2388-2395.
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