Determining The Uncertainty Of Ionospheric Corrections For Users In Wide Area Augmentation Systems

A. J. Mannucci, C. M. Ho, B. A. Iijima, U. J. Lindqwister, X. Pi, B. D. Wilson

Abstract:	Broadcast messages of the FAA’s Wide Area Augmentation System (WAAS) include the grid ionosphere vertical error (GIVE). The GPS signal delay due to the ionosphere is estimated in real-time at each of the WAAS grid points; GIVE values bound the estimation error. In the overall WAAS architecture, GIVE is not used directly but as an intermediate step in computations of slant range error bounds for users. Therefore, WAAS performance should improve if the GIVE algorithm takes the user computation into account. We have developed a heuristic model of the systematic errors incurred when user slant delays are inferred from vertical ionosphere delays at fixed grid points. These systematic errors depend on real-time ionospheric conditions that vary widely over time-scales of hours to years (i.e. quiet/storm, day/night, winter/summer, solar-maximum/ solar-minimum). Our heuristic error model uses real-time WAAS reference station data as input to monitor ionospheric conditions and adjust the computed GIVE values accordingly. For example, it is well known that errors converting vertical delays to slant depend at least partially on horizontal gradients of ionosphere delay. Therefore, spatial gradients in the ionosphere are continuously estimated in real-time, and used to vary the GIVE in a regionally specific manner. We will discuss critical features of the algorithm that improve performance at the borders of the continental US and during major ionospheric storms.
Published in:	Proceedings of the 1999 National Technical Meeting of The Institute of Navigation January 25 - 27, 1999 Catamaran Resort Hotel San Diego, CA
Pages:	761 - 768
Cite this article:	Mannucci, A. J., Ho, C. M., Iijima, B. A., Lindqwister, U. J., Pi, X., Wilson, B. D., "Determining The Uncertainty Of Ionospheric Corrections For Users In Wide Area Augmentation Systems," Proceedings of the 1999 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1999, pp. 761-768.
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