WAAS Availability and Performance at High Latitudes

S. Skone, A. Coster, V. Hoyle, C. Laurin

Abstract:	Auroral activity is a concern for reliable operation of the WAAS (Wide Area Augmentation System) at high latitudes. Auroral substorms are characterized by increased spatial and temporal decorrelations of ionospheric range delay, which may be difficult to model using a wide area ionosphere grid approach. Auroral activity is also characterized by the presence of smallscale irregularities in electron density associated with scintillations. Tracking of the WAAS geostationary downlink may be disrupted during scintillation events. Of particular interest is the relationship of an effect known as storm enhanced density (SED) to the observed scintillation levels and the WAAS ionosphere model. SED is a geomagnetic storm phenomenon, frequently characterized by a plume of enhanced total electron content (TEC) moving northward and westward out of the larger region of enhanced TEC initiating in the southeast corner of the U.S. Sharp gradients in the TEC are associated along the borders of these SED plumes and at the boundaries of the larger TEC region extending across the southern U.S. A typical SED plume is observed forming in the New England region and extending across the Great Lakes into central Canada. In order to study the effects of the high latitude ionospheric activity on GPS applications, the University of Calgary currently operates a Canadian GPS Network for Ionosphere Monitoring (CANGIM). Three reference sites currently cover approximately 1500 km in the North- South direction, allowing observation of both the auroral and sub-auroral regions. These reference sites are equipped with specialized WAAS-capable dual-frequency GPS receivers which provide estimates of scintillation parameters in addition to raw GPS observations. In this paper, the impact of a severe geomagnetic storm event is investigated, with a focus on WAAS geostationary downlink availability in the auroral region, and WAAS ionosphere model accuracies in the mid- through high-latitudes. The WAAS signal availability is assessed using the CANGIM data, and outages of more than 20 minutes are observed in the signal tracking for a NovAtel MPC receiver at Calgary. The WAAS ionosphere corrections are compared with a highresolution TEC model derived from 200 GPS reference stations in North America. Discrepancies of up to 4 m are observed between the two North American TEC maps. These errors are observed to approach WAAS grid ionospheric vertical error (GIVE) bounds near the region of SED.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1279 - 1287
Cite this article:	Skone, S., Coster, A., Hoyle, V., Laurin, C., "WAAS Availability and Performance at High Latitudes," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1279-1287.
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