Ionospheric Effects on GPS Navigation

K. M. Groves, S. Basu, G. J. Bishop, E. J. Weber and J. M. Quinn

Abstract:	Ionospheric effects on radio wave propagation, including amplitude and phase scintillation and group delay, have been recognized and studied for many years. The magnitude of these effects is known to vary dramatically as a function of solar output and magnetic activity. Because the use of GPS for navigation purposes was not widespread during the last maximum in the solar activity cycle, particularly in high-latitude and equatorial regions where the effects of ionospheric disturbances are most severe, the maximum impact of the ionosphere on current GPS applications remains unknown. UHF and L-band scintillation measurements have been acquired routinely over the last solar cycle to characterize the global scintillation environment under varying geophysical conditions. Over an appreciable fraction of the earth’s surface, approximately f 20” magnetic latitude, L-band fades in excess of 20 dB are not uncommon during the solar maximum period. Amplitude changes of this magnitude are likely to cause disruptions to one or more individual GPS satellite links, but the net effect on GPS performance is yet to be determined. A measurement campaign was conducted near Antofagasta, Chile in September 1994 to characterize equatorial ionospheric disturbances and assess their effects on selected satellite- based communication and navigation systems. Although the data were collected during benign solar conditions, substantial fluctuations (6-8 dB) of GPS L-band (Ll) signals were observed. An example of L-band scintillation during solar maximum conditions is presented from which it may be possible to estimate the impacts on GPS navigation systems expected during the next solar maximum period around the year 2000. Efforts to quantify scintillation-induced errors and simulate GPS performance in severe scintillation environments are in progress.
Published in:	Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996) June 19 - 21, 1996 Royal Sonesta Hotel Cambridge, MA
Pages:	583 - 591
Cite this article:	Groves, K. M., Basu, S., Bishop, G. J., Weber, E. J., Quinn, J. M., "Ionospheric Effects on GPS Navigation," Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996), Cambridge, MA, June 1996, pp. 583-591.
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