Precise aircraft positioning by fast ambiguity resolution using improved troposphere modeling

F.J.G. Boon, P.J. de Jonge, C.C.J.M. Tiberius

Abstract:	Landing aircraft at night or under poor weather conditions requires highly accurate and precise information on the position of the aircraft with respect to the runway. The Microwave Landing System (MLS) was the intended successor to the Instrument Landing System (ILS) until GPS reached full operational capability. GPS has considerable advantages over MLS both in installation cost and maintenance aspects. The FAA has already approved GPS as a Landing System for the least stringent landing conditions: Category I. Real time high-accuracy GPS based positioning seems within reach due to recently developed methods, e.g. LAMBDA, which allow fast and efficient recovery of the GPS carrier phase ambiguities. Results from preliminary field tests with a vehicle on the road and a small aircraft, performed by Delft University of Technology and the Dutch National Aerospace Laboratory, indicated the feasibility of such a system. These tests were performed with geodetic dual frequency receivers in a typical single baseline setup with a solution based on an epoch by epoch basis. The resulting position of these vehicles had an accuracy of 10 centimeters or better in real time. The correct integer ambiguity vector was estimated in 80% of all epochs or even more. However, recent tests with airliner-type aircraft during landing approaches at the national airport Schiphol failed to duplicate this success. The tropospheric delay can play an important role in the aircraft type application [Brown, 1994]. Due to the rapid pressure fall with increasing altitude, the GPS measurements recorded at the aircraft experience a smaller tropospheric delay than those recorded at ground level. An altitude difference of 500 meters between the aircraft and the reference station at ground level can result in a relative tropospheric delay of a few decimeters. To gain insight into the importance of troposphere modeling for this application, various troposphere models were applied. This paper quantifies the effect of the tropospheric delay in precise aircraft navigation. Results are given for three cases: without troposphere modeling, for a classic troposphere model and for new mapping functions as described by Niell [1996]. These show that the use of a troposphere model has a distinct benefit on the ambiguity resolution success rate.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	1877 - 1884
Cite this article:	Boon, F.J.G., de Jonge, P.J., Tiberius, C.C.J.M., "Precise aircraft positioning by fast ambiguity resolution using improved troposphere modeling," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 1877-1884.
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