Ionospheric Modeling for WADGPS at Northern Latitudes

Peter J. Stewart and Richard B. Langley

Abstract:	Much work has been undertaken and published on ionospheric modeling for Wide Area DGPS (WADGPS) systems such as the FAA-sponsored Wide Area Augmentation System (WAAS). In mid-latitude regions, typical spatial and temporal variations in ionospheric delay tend to be minimal, and proposed ionospheric models can be broadcast as a set of grid node values along with associated error bounds. Outside of these nominally “quiet” regions however, specifically in the equatorial and auroral zones, the ionosphere is considerably more active, with greater variability both in time and space. Scintillation effects caused by rapid fluctuations in ionization are more prevalent in these zones, and as such, the mitigation of ionospheric delay effects in any WADGPS system which seeks to cover the low or high latitudes may require a more sophisticated modeling process than that for mid-latitude regions. As part of research being carried out at the University of New Brunswick on propagation media effects on WAAS, we are examining the requirements for extending and augmenting the WAAS ionospheric modelling approach to cover Canadian airspace. This work involves identifying and evaluating particular algorithms for the creation of ionospheric delay values and associated error bounds in geographical areas in, and close to, the active auroral zone. In this paper we will identify the specific problems that are associated with ionospheric modelling at high latitudes and over the range of solar activity intensities. Proposed augmentations to be considered include dynamic shell height modelling to enable better performance during auroral storms, and denser grid spacing to take account of larger spatial gradients in the auroral zone. An analysis of grid point availability is presented, showing the limited coverage afforded in northern Canada by the current reference receiver networks.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	757 - 765
Cite this article:	Stewart, Peter J., Langley, Richard B., "Ionospheric Modeling for WADGPS at Northern Latitudes," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 757-765.
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