An Adaptive WADGPS Ionospheric Grid Model for the Auroral Region

S. Skone

Abstract:	By using a number of reference stations, each equipped with a dual frequency receiver, it is possible to estimate values of vertical ionospheric delay (or, equivalently, total electron content) at a set of designated grid points. This type of ionosphere delay modeling is employed in Wide Area Differential GPS (WADGPS) Networks, where delay values at grid points are determined in an adjustment incorporating all receiver-satellite line-of-sight observations. These models can suffer degraded performance in regions, such as the auroral zone, where temporal processes may vary significantly from model assumptions. The auroral zone is characterized by magnetospheric substorms and similar phenomena, in which localised enhancments and depletions of electron density occur. Such events are often associated with small-scale variations in total electron content (TEC), which are difficult to model. The auroral oval is located at high latitudes, and can extend several degrees southward under significantly disturbed levels of ionospheric activity. TEC variations in the auroral zone are therefore significant concerns for WADGPS systems operating in Canada, Europe, and Alaska. In order to achieve optimal ionospheric grid accuracies in the auroral zone, model parameters must be consistent with local ionospheric activity. Existing grid models are generally based on parameters derived for average ionospheric conditions, and thus may not be valid for enhanced levels of ionospheric activity. It is possible, however, to derive information about ionospheric processes in real time, using available TEC observations from stations in the network. In this paper, a revised grid algorithm is proposed, in which the ionosphere grid model is adapted over time. In particular, system model parameters are estimated from observed trends in local TEC observations. System models for each grid point are allowed to vary independently, such that each grid point estimate of TEC is consistent with local ionospheric conditions. The revised model is tested using data from the Natural Resources Canada (NRCan) wide area network, during the period April - October 1996. Grid delay accuracies were improved using the adaptive model, with rms values of .24m, as compared with .33m for a standard grid model.
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:	185 - 194
Cite this article:	Skone, S., "An Adaptive WADGPS Ionospheric Grid Model for the Auroral Region," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 185-194.
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