Ionospheric Correlation Analysis for WAAS: Quiet and Stormy

Andrew Hansen, Juan Blanch, Todd Walter and Per Enge

Abstract: Dual-f~equency measurements made with wide area GPS reference networks provide extremely precise and geographically diverse observations of the ionosphere. While these measurements amount to integrals along a line of sight, coordinated measurements can be brought into a single observation framework for modelling the ionosphere. In WAAS, one this is accomplished with one simplifying assumption, namely the thin-shell approximation. While this approximation has some limitations it is suitable for many applications, one of which is the ionospheric differential correction in the Federal Aviation Administration's Wide Area Augmentation System (WAAS) for GPS. The WAAS application was in fact the motivation for this correlation analysis. The correlation model directly supports the ionospheric irregularity detection process as part of the WAAS integrity algorithms. Beyond WAAS, we feel that both the procedures and the results would be useful to the general ionospheric community who have a great deal of GPS data readily available or would like to fuse disparate data sources together. We give here a description of the measurement processing for noise and multipath removal via a triple threaded reference network, the extended additive model, and its utility in the irregularity detector. We present correlation analyses of measurements made during both nominal (quiet) and disturbed (stormy) ionospheric conditions. In particular, we address the ionospheric activity that occurred 6-8 April 2000 and 15-16 July 2000. This data represents the most extreme conditions yet experienced in the current solar cycle.
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: 634 - 642
Cite this article: Hansen, Andrew, Blanch, Juan, Walter, Todd, Enge, Per, "Ionospheric Correlation Analysis for WAAS: Quiet and Stormy," 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. 634-642.
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