WAAS Performance Improvement with a New Undersampled Ionospheric Gradient Threat Model Metric

Nitin Pandya, Michael Gran, and Ephrem Paredes

Abstract:	The magnitudes of the Vertical Protection Levels (VPLs) of the Wide-Area Augmentation System (WAAS) are primarily driven by the magnitudes of the Grid Ionospheric Vertical Errors (GIVEs), which are error bounds for the WAAS estimates of vertical ionospheric delays. The GIVEs must be large enough to protect against two categories of ionospheric gradients: sampled and undersampled. The sampled gradients are those that are measured by the available Ionospheric Pierce Points (IPPs). Undersampled gradients are between or beyond the available station IPPs. The GIVEs must be inflated when the system has few or no IPPs in a region of the local ionosphere to bound undersampled gradient threats. An undersampled ionospheric gradient threat model, a function of metrics that characterize these regions, was developed to bound these possible undersampled gradients. The efficiency of the threat model metrics in identifying threatening undersampled geometries is critical in determining the performance of WAAS. WAAS will be updated with a more efficient threat model metric, decreasing the magnitudes of the GIVEs and substantially improving system performance.
Published in:	Proceedings of the 2007 National Technical Meeting of The Institute of Navigation January 22 - 24, 2007 The Catamaran Resort Hotel San Diego, CA
Pages:	291 - 304
Cite this article:	Pandya, Nitin, Gran, Michael, Paredes, Ephrem, "WAAS Performance Improvement with a New Undersampled Ionospheric Gradient Threat Model Metric," Proceedings of the 2007 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2007, pp. 291-304.
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