Wide Area Navigation Algorithm for Marine DGPS Users under Disturbed Ionospheric Conditions

S. Skone, R. Yousuf and A. Coster

Abstract:	Under normal operating conditions marine DGPS horizontal positioning accuracies on the order of several meters are achieved in North America. Such accuracies are well within the tolerance of 10 m (95%) specified by the Canadian and United States Coast Guard. Under high levels of ionospheric activity, however, significant degradations in DGPS positioning accuracies can occur. Marine DGPS operations in North America are particularly susceptible to such effects, where a feature known as storm enhanced density is observed during ionospheric storm events. This feature is a localized enhancement of total electron content (TEC) extending northwest through the mid-latitudes. Extremely large gradients are associated with this feature, leading to large differential positioning errors for the single reference station DGPS approach. Wide area ionosphere models have been developed to model and mitigate local ionospheric effects. Such models are based on dual frequency observations from a sparse network of GPS reference stations. In the most simple wide area DGPS algorithms (WADGPS), a measurement domain approach is employed – in which DGPS range corrections are computed for each reference station within the network and a weighted mean of these corrections is estimated to derive optimal range corrections at a user’s location. The scalar range corrections represent all sources of ranging error (e.g. clock, orbital and ionospheric errors). Depending on the number of stations, and the station spacing, such models may improve positioning accuracies by a factor of three or more. Networks of DGPS reference stations operated by marine DGPS service providers may be used in such an approach, with significant benefit for marine users. In this paper we assess the benefit of employing a WADGPS technique for marine users in North America. We quantify the impact of severe ionospheric storm events on marine DGPS users by processing baselines of varying lengths using existing North American GPS reference stations. Wide area techniques are then evaluated using sub-networks of reference stations in North America, and these results are compared with the standard single-baseline DGPS approach. Results indicate significant improvement in positioning accuracies using a wide area approach, with potential for increased availability and continuity of marine DGPS services.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1256 - 1265
Cite this article:	Skone, S., Yousuf, R., Coster, A., "Wide Area Navigation Algorithm for Marine DGPS Users under Disturbed Ionospheric Conditions," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1256-1265.
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