Variations in Ionospheric Range Error With GPS Look Direction

Gregory J. Bishop, David S. Coca and Clayton Coker

Abstract:	ionospheric total electron content (TEC) causes range errors In single-frequency GPS measurements and in other trans-Ionospheric RF systems. The GPS ionospheric correction model, broadcast in the downiink message, has been shown to provide an approximate 50% correction for these errors, on a statistical basis, in the middle-latitude regions such as CONUS. There are several geographic regions outside the mid-latitudes where the geophysical behavior of the ionosphere is markedly different, and the GPS correction model will be less accurate. In fact, the geographic area of the Ionosphere that can be observed from a single GPS site, tracking satellites to very low elevation angles, is large enough that a site nominally in the mid-latitudes will often view many GPS satellites through ionospheric effects from a less stable region, impacting range error correction accuracy. Only limited quantities of data are available to examine the effects of look direction on ionospheric range errors. This paper will examine some of this data, from sites that are outside or at the edge of the mid-latitudes. Measures of TEC variability will be discussed in the context of observed mid-latitude variability and the GPS correction model.
Published in:	Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991) September 11 - 13, 1991 Albuquerque, NM
Pages:	1045 - 1054
Cite this article:	Bishop, Gregory J., Coca, David S., Coker, Clayton, "Variations in Ionospheric Range Error With GPS Look Direction," Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991), Albuquerque, NM, September 1991, pp. 1045-1054.
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