Weighting Ionospheric Corrections to Improve Fast GPS Positioning Over Medium Distances

Dennis Odijk

Abstract:	The success of precise GPS positioning over long baselines depends on the ability of resolving the integer phase ambiguities when short observation time spans are required. The ionosphere is the major error source for these kind of positioning problems and due to the current maximum of solar activity the ionospheric delay errors in GPS signals can be much larger than in periods of minimum activity. When measurements are carried out in the vicinity of a permanent GPS network, then from the long-time data of these permanent stations precise ionospheric delays can be estimated. Next, these ionospheric estimates at the permanent stations can be interpolated to the location of a user operating within the area to correct the user’s measurements. In this article the performance of these ionospheric corrections is tested in terms of improvement of ambiguity resolution at the user’s site. For permanent networks with a large inter-station spacing (100-200 km), the difference between the interpolated ionospheric corrections and the real ionospheric delay in the user’s data can be too large and may hamper a fast estimation of the integer ambiguities. A way to improve this performance is to weight the ionospheric corrections in the adjustment of the observations, instead of treating them in a deterministic way. These ionospheric weights can be implemented by an extension of the stochastic model of the GPS observations. Results of this technique show that for baselines for which the distance to the nearest permanent station can be up to 75 km, the needed observation time could be reduced to only 5 minutes when a-priori ionospheric weights were set up as function of the baseline length.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	1113 - 1123
Cite this article:	Odijk, Dennis, "Weighting Ionospheric Corrections to Improve Fast GPS Positioning Over Medium Distances," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 1113-1123.
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