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

利用地理调查所运营的全球定位系统（GPS）接收器网络GEONET的观测数据，开发了一个在日本派生和分发总电子含量（TEC）数据的系统。GEONET每30秒从大约1000个接收器上获得GPS卫星的定位数据。考虑视距与电离层之间的几何关系，将观测到的定位数据转换为垂直TEC。为了减少这种转换带来的误差，在此过程中省略了低仰角的数据。利用GEONET TEC数据，以30秒的时间分辨率和0.15度的经纬度空间分辨率，导出了日本上空TEC的二维分布。所得TEC的精度估计为2-4 × 10^<16>电子/m^2。用最小二乘拟合方法估计了发射机和接收机内部的电偏，并从观测到的TEC数据中减去了电偏。对1999年4月以来的所有GEONET数据进行了处理，并对每天的新数据进行了处理。派生的TEC数据存储在一个数据库中，并可通过WWW访问http://stegps.kugi.kyoto-u.ac.jp/。该数据库提供了四种类型的数据：ATEC（每个接收地的TEC绝对值）、TEC（每个接收地包含偏差的TEC数据）、AGRJD（日本地区绝对TEC的二维分布）和GRID（扰动TEC的二维分布）。TEC的二维地图也储存在数据库中。该数据库具有交互式绘图页面，可在任何给定日期和位置绘制TEC绘图。利用该数据库，对中纬度电离层进行了若干研究。利用GEONET TEC数据探测到中尺度的移动电离层扰动，并与其他测量数据（如空气辉光成像仪和MU雷达）进行了比较。利用GEONET TEC资料对地磁风暴期间的电离层扰动进行了详细研究。少

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