Ionospheric Warning System for Marine DGPS Users

S. Skone

Abstract:	Under normal operating conditions marine DGPS horizontal positioning accuracies on the order of several meters are achieved in North America. Degradations in positioning accuracy can occur during enhanced ionospheric activity. An ionospheric phenomenon known as storm enhanced density (SED) is observed to develop in the mid- to high-latitudes during ionospheric storm events. Very large gradients are observed in the vicinity of this feature with DGPS positioning errors increased by a factor of 10-30 versus quiet conditions. While the SED phenomenon typically develops in the eastern United States over a period of hours, extending northwest into Canada, the specific evolution of a given event and the magnitude of expected impact are not generally predictable. The only method to monitor the development of SED, and associated severe gradients of interest for DGPS users, is to compute ionospheric maps in real-time. Local gradients can then be computed for various geographic regions from North American maps of ionosphere delay. Sources of real-time ionospheric information include the Wide Area Augmentation System (WAAS) and the Canadian GPS•C service. These are wide area differential GPS systems in which ionosphere maps and associated error bounds are derived for North America. Both the WAAS and GPS•C ionosphere maps are available via geostationary downlink in RTCA format. By using WAAS and/or GPS•C-capable receivers at fixed sites in North America, the full North American ionosphere maps can be decoded and manipulated. Raw observations from the GPS•C sites can also be obtained for derivation of ionospheric information. In this paper, a real-time ionosphere warning system is investigated for North American DGPS users based on available real-time data. It is determined that the WAAS and GPS•C ionosphere maps do not provide adequate spatial resolution to identify local ionosphere gradients. The raw data from GPS•C reference sites, however, can be used to determine the location and magnitude of large ionosphere gradients and infer the expected impact on DGPS users. Potential exists to issue marine user warnings based on this method. Results of this work can readily be extended to land DGPS applications, such as the NDGPS service in the United States.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	1992 - 2005
Cite this article:	Skone, S., "Ionospheric Warning System for Marine DGPS Users," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 1992-2005.
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