Wide Area Ionospheric Delay Corrections Under Ionospheric Storm Conditions

A. J. Mannucci, B. A. Iijima, B. D. Wilson, S. Peck, R. Ahmadi, M. Hagen

Abstract:	The Federal Aviation Administration’s Wide-m augmentation system (WAAS) for GPS positioning requires near real-time calibration of ionospheric’ vertical delays at a set of Earth-fixed grid points. These delays, which can exceed 15 meters under solar maximum conditions, are transmitted to users every 5 minutes to improve single-frequency user positioning. The grid delays will be estimated using the WAAS Ionospheric Software (WIS) developed jointly by JPL and Hughes, based on ionospheric delay measurements from 24 dual- frequency GPS reference receivers distributed throughout the WAAS coverage volume. We have investigated the performance of these algorithms under ionospheric storm conditions, when meeting accuracy goals is expected to be most challenging. Testing of ionospheric correction algorithms is complicated by the extreme variability of the ionosphere, arising from the 11 year solar cycle and the intermittent occurrence of ionospheric storms. Recently completed tests of the WIS using data from a real-time network of eight reference receivers in the continental United Stated indicate accuracies in the range of 15-20 cm (RMS). However, these tests were conducted using current GPS data sets (g/96), near the minimum of the solar cycle when ionospheric conditions are favorable. We present the results of additional tests under more challenging conditions nearer to solar maximum, focusing on geomagnetically disturbed periods, using archived GPS data (processed in a real-time mode) obtained from a global network of dual-frequency receivers. The intent is to characterize the accuracy of WIS under a wide variety of geomagnetic and solar activity conditions. In the storm cases examined here, the maximum accuracy degradation was at most a factor of 2-3 relative to recent quiet time tests. These results suggest that accuracy requirements for precision approach may still be met during significant storms.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	871 - 882
Cite this article:	Mannucci, A. J., Iijima, B. A., Wilson, B. D., Peck, S., Ahmadi, R., Hagen, M., "Wide Area Ionospheric Delay Corrections Under Ionospheric Storm Conditions," Proceedings of the 1997 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1997, pp. 871-882.
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