日本におけるGPS衛星電波の局所的な電離圏遅延勾配の背景場の評価

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This paper presents evaluations of ionospheric delay spatial gradients with a horizontal scale of several tens kilometers using a TEC (total electron content) data base of Kyoto University based on GEONET (GPS earth observation network) observations. GBAS (ground-based augmentation system) is a system based on the differential GPS technique for aircraft precision approach in the vicinity of an airport with a single frequency of GPS L1-C/A code signal. To support the final phase of precision approach, high reliability is required for a GBAS. However, it is recognized that a large ionospheric gradient could result in significant positioning error. In safety design of a GBAS algorithm to generate messages broadcast to aircraft, it is necessary to distinguish an anomalous ionospheric condition from a nominal. We analyzed ionospheric delay data to evaluate the nominal ionospheric gradient in Japan for the period from 1998 to 2009. We found that the ionospheric gradient to overbound the occurrence probability density function was 8.77mm/km. This result is useful not only to GBAS but also single frequency GPS users.
2010-09-25