Ambiguity Resolution Over Long Baselines for Airborne Differential GPS Positioning

W. B. Krabill, J. G. Sonntag and C. F. Martin

Abstract:	A technique has been developed for reliably resolving GPS carrier phase ambiguities over long baselines in an airborne kinematic application. The technique has been used to compute aircraft trajectories accurate to the sub-decimeter level in support of NASA’s Arctic Ice Mapping (AIM) Program. A total of 25 missions from the 1993 and 1994 field seasons, as well as several missions from the 1995 field season, have been successfully processed using this method. During these missions, the aircraft routinely flew 1000 km or more from the fixed reference receiver, although it began and ended the missions within 2-3 km of it. The long baselines and prolonged duration of the missions, often seven hours or more of flying time, complicated the ambiguity resolution problem in two key ways. First, Ll and L2 ambiguities had to be resolved for satellites tracked solely in-flight using ionosphere-free dual frequency data. Second, since no single satellite could be tracked for the entire duration of the long missions, it was necessary to reconcile the otherwise independent pre- and post-flight ambiguity solutions using the overlap provided by the in-flight data. To deal with these complications, the technique utilizes a combination of information t?om pre-flight static solutions, in-flight ambiguity and trajectory estimation, and post-flight static solutions in order to determine a consistent set of integer ambiguities for the entire mission. Dual-frequency carrier phase measurements are supplemented with dual-frequency pseudoranges in order to resolve the ambiguities of the satellites tracked only in flight, as well as to reconcile and merge the pre- and post-flight solutions with each other and with the in-flight solution.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	1117 - 1126
Cite this article:	Krabill, W. B., Sonntag, J. G., Martin, C. F., "Ambiguity Resolution Over Long Baselines for Airborne Differential GPS Positioning," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 1117-1126.
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