Robust Detection of Ionospheric Irregularities

Todd Walter, Andrew Hansen, Juan Blanch, Per Enge, Tony Mannucci, Xiaoqing Pi, Larry Sparks, Byron Iijima, Bakry El-Arini, Roland Lejeune, Mine Hagen, Eric Altshuler, Rob Fries and Aleck Chu

Abstract:	The Wide Area Augmentation System (WAAS) will provide real-time differential GPS corrections and integrity information for aircraft navigation use. The most stringent application of this system will be precision approach, where the system guides the aircraft to within a few hundred feet of the ground. Precision approach operations require the use of differential ionospheric corrections. WAAS must incorporate information from reference stations to create a correction map of the ionosphere. More importantly, this map must contain confidence bounds describing the integrity of the corrections. The confidence bounds must be large enough to describe the error in the correction, but tight enough to allow the operation to proceed. The difficulty in generating these corrections is that the reference station measurements are not co-located with the aviation user measurements. For an undisturbed ionosphere over the Conterminous United States (CONUS), this is not a problem as the ionosphere is nominally well behaved. However, a concern is that irregularities in the ionosphere will decrease the correlation between the ionosphere observed by the reference stations and that seen by the user. Therefore, it is essential to detect when such irregularities may be present and adjust the confidence bounds accordingly. The approach outlined in this paper conservatively bounds the ionospheric errors even for the worst observed ionospheric conditions to date, using data sets taken from the operational receivers in the WAAS reference station network. As we progress through the current solar cycle and gather more data on the behavior of the ionosphere, many of our pessimistic assumptions will be relaxed. This will result in higher availability while maintaining full integrity.
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:	209 - 218
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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