Ionospheric Correction Using Tomography

Andrew J. Hansen, Todd Walter, Per Enge

Abstract:	The most demanding application of wide area differential corrections to GPS is vertical positioning of aircraft on precision approach. Here the Wide Area Augmentation System (WAAS) combines accuracy requirements on the order of ones of meters with safety life integrity requirements which specify that any vertical position errors greater than the Vertical Protection Limit be enunciated to the flight crew within six seconds. The ionosphere is the foremost impediment to satisfying these requirements. Stanford, as a member of the National Satellite Test Bed (NSTB), is developing techniques for estimating the ionosphere in real-time. Previous research has established a connection between ionospheric error and vertical positioning error within the framework modal decomposition. Ionospheric tomography is a natural extension of modal decomposition to the estimation of the ionosphere’s three-dimensional electron density. We present a tomographic estimation algorithm and its implementation over the NSTB network. This estimator supplies not only corrections to the user but also appropriate confidence information for predicting the accuracy of those corrections in the aircraft. The tomographic approach to ionospheric correction obviates the troublesome obliquity factor associated with typical gridded vertical delay algorithms. The capability of ionospheric tomography is demonstrated by a time series of 3D electron density reconstructions over the Coterminous United States (CONUS). The accuracy, integrity, and availability afforded the user by this approach is quantified through application on live NSTB observations.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	249 - 257
Cite this article:	Hansen, Andrew J., Walter, Todd, Enge, Per, "Ionospheric Correction Using Tomography," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 249-257.
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