Observed Ionospheric Dependence on Solar Activity: Implications for a New Single Frequency GPS User Algorithm

Patricia H. Doherty, Dwight T. Decker, John A. Klobuchar, David N. Anderson, Brian D. Wilson

Abstract:	Radio waves propagating through the ionosphere suffer an additional time delay as a result of their encounter with the Total Electron Content (TEC) along the path from the satellite to a ground station. TEC is a highly variable and complex region that is a function of geographic location, local time, season, geomagnetic activity and solar activity. For the dual frequency GPS user, the range error caused by the ionosphere is corrected for by using the signals of both the GPS Ll and L2 frequencies. For the single frequency GPS user, the Ionospheric Correction Algorithm (ICA) was developed to correct for approximately 50% rms of the error (Klobuchar, 1975, 1987). The ICA was developed in 1975 using the Bent Model (Llewellan and Bent? 1973), a state of the art empirical ionospheric model that was based on topside shape measurements recorded during an average solar cycle. Solar cycle maximum values since that period have been much higher. As a result, the ICA does not adequately represent periods of extremely high solar maximum activity. The aim of this paper is to aide in the development of an improved GPS single frequency user algorithm by defining an improved fit between TEC and long term solar activity and to determine if that fit changes for different seasons and geographic locations. This study is accomplished by correlating ionospheric measurements recorded at several widely spaced geographic locations over the last four solar cycles with various functions of the 10.7 cm solar flux (FlO.,). The results of this study will be immportant in the development of new coefficients to describe worldwide ionspheric behavior for an improved single frequency GPS user algorithm.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	565 - 574
Cite this article:	Doherty, Patricia H., Decker, Dwight T., Klobuchar, John A., Anderson, David N., Wilson, Brian D., "Observed Ionospheric Dependence on Solar Activity: Implications for a New Single Frequency GPS User Algorithm," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 565-574.
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