Upcoming Ionospheric Impacts on GPS at Solar Max: What do we know / What do we need?

Gregory Bishop, Santimay Basu, Keith Groves, Matthew Smitham, Kirk Lehneis, Denice Jacobs, Paul Gehred, Dana Howell, Gregory Bainum and Derrill Goldizen

Abstract:	Can the ionosphere have important impacts on GPS, even at solar maximum? The answer appears to be a qualified yes, in particular applications and circumstances. However, the real answer is worse, namely, experts cannot yet truly answer the question in a general way due to its complexity. Analysis of each application is complicated, and the existence of any mission impact depends on a number of factors. These factors include the system’s mission requirements, the characteristics of the GPS receiver, the time in the solar cycle, the season of the year, your location on earth, as well as what is occurring in the ionosphere. Ionospheric scintillation, caused by small-scale irregularities in the ionospheric electron density that can disturb (or “scintillate”) the amplitude and phase of radio signals that traverse it, can at times cause severe fades or rapid phase gradients that exceed receivers’ capability to hold “lock* on the signal. Several cases of such “loss-of-lockV conditions have been reported. Such impacts, then, are not a question of accuracy so much as availability, and are an issue for integrity monitoring, at least. However, for DGPS an accuracy issue can, in fact, arise from high decorrelation of ionospheric range errors due to large-scale ionospheric structures in certain regions and times. In this paper we will review what is known of nature of ionospheric scintillation and spatial decorrelation, and how these phenomena affect GPS signals. We then address in detail the factors that must be evaluated in assessing potential mission impact for a specific GPS application. A status review is given for ongoing efforts showing current progress/shortfalls in determining ionospheric impacts on GPS navigation and providing warning/forecasting of ionospheric “weather” threat conditions.
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:	595 - 604
Cite this article:	Bishop, Gregory, Basu, Santimay, Groves, Keith, Smitham, Matthew, Lehneis, Kirk, Jacobs, Denice, Gehred, Paul, Howell, Dana, Bainum, Gregory, Goldizen, Derrill, "Upcoming Ionospheric Impacts on GPS at Solar Max: What do we know / What do we need?," 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. 595-604.
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