Analysis of Ionosphere Gradient Using Japan GEONET Data

Hiroyuki Konno, Sam Pullen, Ming Luo and Per Enge

Abstract:	Large spatial gradients in ionosphere delay are a potentially threatening error source for the Local Area Augmentation System (LAAS). Therefore a better understanding of the ionosphere behavior during strong magnetic storms is crucial for LAAS so that it can more accurately evaluate its integrity and availability during these events. In order to obtain spatially-dense information on severe ionosphere delays, we use data from the Japan GPS Earth Observation Network (GEONET). GEONET is a very dense network of dual-frequency GPS receivers with more than 1200 receivers distributed across Japan. This density provides a significant advantage to the investigation of local ionosphere behavior. There are two major difficulties with the analysis of the GEONET data. The first issue is calculating accurate ionosphere delay measurements from the raw data provided by GEONET. We use the carrier-phase measurements of L1 and L2 while applying a calibration method for the interfrequency bias (IFB) that always appears in the processing of the dual-frequency data. The second issue is to screen out “artificial anomalies” that are due to GEONET receiver errors. Since the GEONET database is very large, partial data loss or erroneous measurements are occasionally included in the raw data. This poor-quality data can result in large errors in ionosphere delay calculations, and as a consequence, the estimated delays may appear to be ionosphere anomalies in the analysis. Based on identifying the geometrical differences between real and artificial gradients, we developed an error-screening technique that automatically excludes artificial gradients and output only actual large gradients from the huge GEONET database. We investigated five strong magnetic storms using the GEONET data. We found several instances of ionosphere spatial gradients much lager than normal during these storms. However, we found no gradients extreme enough to lead to unacceptable user errors for LAAS. Through these analyses, we have demonstrated the effectiveness of our method as a tool to analyze ionosphere behavior based upon GEONET data.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	1118 - 1129
Cite this article:	Konno, Hiroyuki, Pullen, Sam, Luo, Ming, Enge, Per, "Analysis of Ionosphere Gradient Using Japan GEONET Data," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 1118-1129.
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