WAAS Performance Investigation for Disturbed Ionospheric Conditions over Canadian Latitudes

O. Haddad, S. Skone, and L. Sparks

Abstract:	The Wide Area Augmentation System (WAAS) now includes four Reference Stations (WRS) in Canada for improved coverage at high latitudes particularly in eastern Canada. Since the number of the stations in the Canadian region is limited, it is possible that some ionospheric irregularities will be undetected and WAAS performance will be degraded. In order to expand the operation of WAAS over Canadian latitudes, WAAS algorithm performance must be evaluated for challenging ionospheric conditions at the Canadian latitudes to ensure that system requirements are met. For this purpose, different scenarios of challenging ionospheric conditions are simulated over the latitudes of interest based on ionospheric features which have been identified as a major challenge for WAAS called Storm Enhanced Density (SED). Archived data from hundreds of Global Positioning System (GPS) stations across Canada and United States are used to study the spatial characteristics of ionospheric Total Electron Content (TEC) variation during many SED events observed at Canadian latitudes. Two-dimensional TEC maps for such events are produced on 2.5o x 2.5o grids using more than 500 GPS stations over North America, and various characteristics are determined: size of the irregularities, magnitude of TEC values inside the plume, and gradients at the edge of the plume. From these simulated conditions, ionospheric delays are estimated for 24 GPS satellites observed from 29 WRSs in Canada and United States. These observations are provided as input to the WAAS algorithm to obtain WAAS estimated ionospheric corrections and associated integrity bounds at ionospheric grid points. Both the current planar fit and future kriging methods are evaluated. Preliminary results indicate that WAAS bounds all ionospheric errors sufficiently; however, as the ionosphere becomes more active, errors in the estimated ionospheric delays become much larger. Also, within the same simulated scenarios, WAAS availability is degraded in regions of undersampling and high gradients, and integrity bounds are increased in these regions. However, WAAS consistently bounds the errors for high ionospheric delay, regions with undersampled threats, and regions of sharp gradients. Due to the lack of stations in the northern and western regions, the ionosphere cannot be monitored over these regions.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2462 - 2473
Cite this article:	Haddad, O., Skone, S., Sparks, L., "WAAS Performance Investigation for Disturbed Ionospheric Conditions over Canadian Latitudes," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 2462-2473.
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