GPS Range Updates in an Automatic Flight Inspection System: Simulation, Static and Flight Test Results

Cecelia M. Feit

Abstract:	This paper presents the design, implementation, simlation, static test and flight test results of a position estimation technique which uses Global Positioning System (GPS) range up dates in a Flight Inspection application. A square root Ealnm filter estimates the navigation errors in real time, and a modified Bryson- Frazier smother improves these estimates immediately post profile to provide the most accurate in-flight aircraft position for calibration and inspection of en route and final approach navigation aids. The proprietary GPS range update algorithm was designed and developed by Sierra Besearch. Its first application will be for an Automatic Flight Inspection System (AFIS) developed under contract to British Aerospace for the U-125 Flight Inspection Aircraft for the Japanese Defense Agency. The GPS update technique is based on ranges rather than GPS-derived position for several reasons. The most important reason is that this is best way to blend GPS with other update sources, such as DMEs, landmarks, sod precision rummy Barks. Delta range measurements are derived from the satellite and aircraft positions and pseudorange measurements. A set of GPS range updates that can use from one to the maximum number of visible satellites are performed every ten seconds. The Kalman Filter used in the USAF/FAA C-29A and Spanish Air Force Autanatic Flight Inspection Systems designed and built by Sierra Research, was modified to include states for the user clock phase and clock frequency. Error signals, mapping matrices and measurement covariance matrices were derived, along with techniques to account for correlated measurement noise due to Selective Availability (SA). The actual embedded Kalman Filter was tested using a computer simulation which accurately modeled Inertial and GPS errors, including SA. The operational system was tested in a static condition, using real inertial and GPS signals, during a time when SA was enabled. Simulation and static test results show the performance improvenmts which can be expected using GPS range updates in the flight inspection application.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	75 - 86
Cite this article:	Feit, Cecelia M., "GPS Range Updates in an Automatic Flight Inspection System: Simulation, Static and Flight Test Results," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 75-86.
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