A Study of the Ionospheric Effect on GBAS (Ground-Based Augmentation System) Using the Nation-Wide GPS Network Data in Japan

摘要

This paper presents an investigation of spatial gradient of ionospheric delay that has a possibility of affecting GBAS (Ground-Based Augmentation System) using the nationwide and dense GPS network in Japan (GEONET; GPS earth observation network). GBAS is a system based on a differential GPS technique for aircraft precision approach near an airport using C/A pseudorange. In general, ionospheric delay will be removable using correction data set that is generating and transmitting from a ground segment of GBAS. However, a large spatial gradient of ionospheric delay between ground GPS monitoring station and aircraft will be a risk to integrity of GBAS. Therefore, our purpose is to exactly estimate local-scale variation of ionospheric delay. Because Japan is located in lower geomagnetic latitude than geographic latitude, 'Equatorial anomaly' phenomenon is especially remarkable for generating a variation of ionospheric delay gradient in the North-South direction. GEONET is consists of about 1,000 GPS stations using dual-frequency receiver and a typical distance between neighbor stations is about 20 km. We used Total Electron Content (TEC) data of GEONET with a correction of inter-frequency bias that provided from TEC database of Kyoto University, Japan. Firstly, we investigated general characteristic of spatial gradient of ionospheric delay over Japan using TEC data with rough grid and time resolutions. In distribution analysis of the number of times for each magnitude of gradient in the S-N direction, the results were consistent with the matter that growth of equatorial anomaly produced large TEC gradient toward south. Secondly, in order to detect smaller perturbation of spatial gradients, we used 'grid TEC' of TEC database, which sorted from each pierce point into each grid with a spatial resolution of 0.15 degree in longitude and latitude. We calculated and investigated spatial gradient after averaging TEC with a spatial resolution of 1-degree-grid and a time resolution of 15 minutes at the point with the maximum slant path density. The results were consistent with our expectation that small-scale perturbations were correctly represented.