Development of a data processing and distribution system for total electron content data of a GPS receiver network

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A system to derive and distribute Total Electron Content (TEC) data over Japan was developed using the observational data of GEONET, a GPS receiver network operated by Geographical Survey Institute. GEONET obtains positioning data from GPS satellites in every 30 seconds at about 1000 receivers. The observed positioning data were converted to vertical TEC considering the geometry between the line-of-sight and the ionosphere. To reduce errors caused by this conversion, the data with low elevation angles were omitted in this process. Using this GEONET TEC data, two-dimensional distribution of TEC over Japan was derived with 30 seconds of temporal resolution and 0.15 degrees of spatial resolution in latitude and longitude. The accuracy of the derived TEC was estimated to be 2-4x10^<16> electron/m^2. Electrical biases inside of the transmitters and receivers were estimated and subtracted from the observed TEC data with the least-square fitting method. All of GEONET data since April in 1999 … More were processed with this method and newly obtained data are also processed every day. The derived TEC data are stored in a data base and can be accessed through WWW at http://stegps.kugi.kyoto-u.ac.jp/. Four types of data are provided in this data base : ATEC (absolute value of TEC for each receiver), TEC (TEC data for each receiver containing biases), AGRJD (two-dimensional distribution of absolute TEC over Japan) and GRID (two-dimensional distribution of perturbation TEC). Two-dimensional maps of TEC are also stored in the data base. The data base has interactive plot pages to make plots of TEC at any given dates and positions. Using this data base, several studies on the mid-latitude ionosphere were carried out. The medium-scale traveling ionospheric disturbances were detected by the GEONET TEC data and compared with the data by the other measurements, such as air-glow imagers and the MU radar. Ionospheric disturbances during the geomagnetic storm periods were studied in detail with GEONET TEC data. Less