A regional ionospheric TEC mapping technique over China and adjacent areas: GNSS data processing and DINEOF analysis

A technique is developed to derive two-dimensional maps of total electron content (TEC) over China and adjacent areas using Global Navigation Satellite System (GNSS) data from the Crustal Movement Observation Network of China (CMONOC) and the International Global Navigation Satellite System Service (IGS). A revised self-calibration of pseudo-range errors (SCORE) algorithm is used to derive the TEC and to determine the Differential Code Biases (DCBs) simultaneously. The accuracy and validity of this technique is verified in two ways. Firstly, the estimated TEC is compared with the results derived using DCBs from Center for Orbit Determination of Europe (CODE) under different solar activity conditions and seasons; secondly, sample TEC along the receiver-to-satellite ray paths are simulated by NeQuick model and are reprocessed by this TEC derivation technique to make the accuracy test. Two-dimensional maps of vertical TEC of ionospheric pierce points (IPPs) are obtained accordingly with a time resolution of 30 s. The data interpolating empirical orthogonal functions (DINEOF) technique is then used to make the extrapolation for the unknown or missing data points. The optimal EOF modes for data reconstruction are specified via cross-validation method. The regional TEC distribution over China and adjacent areas is scaled into grid size of 1 degrees x 1 degrees for each 5 mm, which can well reflect the characteristic of large-scale regional variations and temporal evolution as well as the small-scale local features of ionosphere.