Wide Area Ionosphere Modeling at Low Latitudes - Specifications and Limitations

S. Skone

Abstract:	Dual frequency GPS receivers enable the estimation of absolute ionospheric delay and total electron content (TEC) along a given satellite signal path. By using a number of reference stations, each equipped with a dual frequency receiver, it is possible to derive a grid of vertical TEC values, in latitude and longitude. This type of ionosphere delay modeling is employed in wide area differential GPS (WADGPS) networks. Such models can suffer degraded performance in regions where large spatial gradients, and irregularities, in TEC exist. Model accuracies may also be limited through the presence of scintillation effects – with compromised data availability. Such issues are a concern in the equatorial region, where electrons are lifted away from the magnetic equator, under the influence of strong electric fields associated with a latitudinally localised electrojet current. Large TEC gradients are present near the resulting equatorial anomaly, with electrodynamic lifting of the equatorial plasma to F region heights of 800 km and beyond. In periods of solar maximum, the anomaly may peak at ¡Ö2100 local time, and gradients in TEC can be considerably larger than dayside values at this secondary diurnal maximum. In this paper, ionosphere modeling (using a wide area approach) is investigated in the equatorial region. Data from ten equatorial stations in the Brazilian geodetic network are considered during recent periods of enhanced ionospheric activity – representative of solar maximum. Limitations in model accuracies are assessed, and the spatial resolution (i.e. grid spacing) necessary to resolve TEC features, and satisfy WADGPS error bounds, is investigated. Issues concerning data availability in the presence of intense scintillations are also discussed. Recommendations for ionosphere modeling specifications are made, for application to future implementation of Satellite-Based Augmentation Systems (SBAS) in the equatorial region.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	643 - 652
Cite this article:	Skone, S., "Wide Area Ionosphere Modeling at Low Latitudes - Specifications and Limitations," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 643-652.
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