Abstract: | Triggered by several severe ionosphere storms that have occurred in recent years, research has been done to studying those anomalies, the physics behind them, and their potential impact on augmented GNSS users. In previous work [1-5], it was found that such ionosphere anomalies can threaten LAAS users under extreme conditions. To determine this, a spatial-gradient “threat model” was established based on ionosphere storm data observed from WAAS and IGS since 2000. Maximum differential user vertical errors were estimated based on this threat model. Although LGF monitors can detect “moving fronts”, so-called “stationary fronts” remain threatening since the LGF may never be able to observe it (e.g., if the ionosphere front stops moving at the worst possible location prior to reaching the LGF). In order to validate the threat model, a comprehensive methodology was developed to analyze WAAS “supertruth” data as well as both raw and JPLprocessed data from the IGS/CORS receiver network to search for anomalous gradients [15]. Anomalous gradients that result from this method were used to populate and validate the LAAS ionosphere spatial gradient "threat model". These data studies show that most of the ionosphere anomalies seem to move reasonably fast relative to the speed of an approaching aircraft. The few data points thought to be stationary were impossible to validate after a thorough investigation. Additional data analysis has been performed to better determine the credibility of the slow-moving segment of the ionosphere spatial anomaly threat space. In this paper, data from the Ohio/Michigan cluster of CORS stations on November 20, 2003 and from the Florida region on October 31, 2003 (UTC) are searched for slow-moving ionosphere events. One data point that stood out was verified by observation at various locations using both the dual-frequency JPL data as well as L1 code-minus-carrier estimation. A threat analysis follows to show the potential impact of this observed threat under various GPS constellation states. A sensitivity study is conducted to show how the impact relies on the upper bound of the slow-moving threat model. A “data replay” analysis is also performed to show the actual LAAS errors that would have occurred at one pair of stations in Florida. Finally, a recommendation is made in for revising the upper bound of the slow-moving threat space. |
Published in: |
Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA |
Pages: | 2337 - 2349 |
Cite this article: | Luo, Ming, Pullen, Sam, Datta-Barua, Seebany, Zhang, Godwin, Walter, Todd, Enge, Per, "LAAS Study of Slow-Moving Ionosphere Anomalies and Their Potential Impacts," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2337-2349. |
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