The Ionospheric Impact of the October 2003 Storm Event on WAAS

Attila Komjathy, Lawrence Sparks, Anthony J. Mannucci, Anthea Coster

Abstract:	The United States Federal Aviation Administration’s (FAA) Wide Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite- Based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Multi-transport Satellite-based Augmentation System (MSAS). Navigation using WAAS requires accurate calibration of ionospheric delays. To provide delay corrections for single frequency GPS users, the wide area differential GPS systems depend upon accurate determination of ionospheric total electron content (TEC) along radio links. Dual-frequency transmissions from GPS satellites have been used for many years to measure and map ionospheric TEC on regional and global scales. The 2003 October solar-terrestrial events are significant not only for their dramatic scale, but also for their unique phasing of solar irradiance and geomagnetic events. During October 28, the solar X-ray and EUV irradiances were exceptionally high while the geomagnetic activity was relatively normal. Conversely, October 29-31 was geomagnetically active while solar irradiances were relatively low. These events had the most severe impact in recent history on the CONUS region and therefore had a significant effect on the WAAS performance. To help better understand the event and its impact on WAAS, we examine in detail the WAAS reference site (WRS) data consisting of triple redundant dual-frequency GPS receivers at 25 different locations within the US. To provide ground-truth, we take advantage of the three colocated GPS receivers at each WAAS reference site. To generate ground-truth and calibrate GPS receiver and transmitter inter-frequency biases, we process the GPS data using the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This software allows us to compute calibrated high resolution observations of TEC. We found ionospheric range delays up to 35 meters for the day-time CONUS during quiet and up to 100 meters during storm time conditions. For quiet day, we obtained WAAS planar fit slant residuals less than 2 meters (0.4 meter RMS) and less than 25 meters (3.4 meter RMS) for the storm day. We also investigated ionospheric gradients, averaged over distances of a few hundred km. The gradients were no larger than 0.5 meter over 100 km for a quiet day. For the storm day, we found gradients at the 4 meter level over 100 km. Similar level gradients are typically observed in the low latitude region for quiet or storm conditions.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1298 - 1307
Cite this article:	Komjathy, Attila, Sparks, Lawrence, Mannucci, Anthony J., Coster, Anthea, "The Ionospheric Impact of the October 2003 Storm Event on WAAS," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1298-1307.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In