Performance Evaluation of DGPS versus SBAS/WADGPS for Marine Users

S. Skone and A. Coster

Abstract:	Marine DGPS services are provided by many government agencies worldwide. Horizontal positioning accuracies on the order of several metres are typically achieved for these systems – well within the specified tolerance of 10 m (95%). Under high levels of ionospheric activity, however, significant degradations in DGPS positioning accuracies can occur. In previous studies for the North American sector, marine DGPS positioning errors were observed to increase by factors of 10-30 under increased ionospheric activity. In particular, gradients of up to 50 ppm are associated with a feature known as storm enhanced density (SED). This feature is a localized enhancement of total electron content (TEC) extending northwest through the mid-latitudes. DGPS positioning errors of 20 m or more have persisted for hours during such events. Satellite-Based Augmentation Systems (SBAS) such as the WAAS also experience degraded positioning accuracies during such events, with horizontal positioning errors of 20-25 m. In this paper we conduct a comparison of horizontal positioning accuracies achieved for SBAS versus marine DGPS networks. In particular, we evaluate WAAS capabilities for marine positioning applications in North America. We also quantify the horizontal DGPS positioning accuracies in North America and Europe during severe geomagnetic storm events. Performance evaluations are conducted using available data from existing GPS networks (IGS, CORS and EUREF). Positioning accuracies are computed for DGPS baselines of lengths in the range 100-200 km within these networks. WAAS positioning accuracies are also computed at selected reference stations within the IGS and CORS networks in North America. WAAS and DGPS horizontal positioning accuracies are then compared during enhanced ionospheric activity in North America. DGPS positioning accuracies are evaluated in Europe under similar disturbed ionospheric conditions. Limitations and error bounds are established under challenging ionospheric conditions.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	1904 - 1913
Cite this article:	Skone, S., Coster, A., "Performance Evaluation of DGPS versus SBAS/WADGPS for Marine Users," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 1904-1913.
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