The Dependence of WAAS Ionospheric Error Bounds upon the Spatial Distribution of GPS Measurements

L. Sparks, A. Komjathy, A.J. Mannucci

Abstract: To attain a higher level of service, the Wide Area Augmentation System (WAAS) for airline navigation must estimate ionospheric delays of Global Positioning System (GPS) signals more accurately and bound their errors more tightly. Undetected ionospheric irregularities that arise under disturbed conditions can become a major source of user delay error. To protect the user from such errors, the error bounds to be broadcast are augmented by an amount derived from an ionospheric threat model. This paper examines the dependence of the threat model upon the spatial distribution of GPS measurements. Spatial configurations of GPS measurements can be characterized in terms of spread metrics. A spread metric gauges the degree to which a given set of measurements covers a given region densely and uniformly. A new metric is introduced here to distinguish more reliably measurement configurations that might fail to sample a significant ionospheric irregularity. Using the new metric to parameterize the spatial threat model, we show that the magnitude of the broadcast error bounds can be reduced. In our initial study the augmentation of the broadcast error bounds that protect the user from undersampled irregularities is reduced, on average, by 32%.
Published in: Proceedings of the 2003 National Technical Meeting of The Institute of Navigation
January 22 - 24, 2003
Disneyland Paradise Pier Hotel
Anaheim, CA
Pages: 719 - 727
Cite this article: Sparks, L., Komjathy, A., Mannucci, A.J., "The Dependence of WAAS Ionospheric Error Bounds upon the Spatial Distribution of GPS Measurements," Proceedings of the 2003 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2003, pp. 719-727.
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