Accuracy assessment of regional ionospheric tomography TEC in China based on GNSS data

To obtain high-precision Total Electron Content (TEC) data for a more in-depth understanding and research of the ionosphere's true characteristics and small-scale variations, this study leveraged ionospheric tomography techniques based on multi-constellation Global Navigation Satellite System (GNSS) data to reconstruct and extract ionospheric TEC from September 5 to 15, 2017, in the Chinese region. The study encompasses both quiet and disturbed ionospheric conditions, providing ample geomagnetic context for evaluating tomographic TEC accuracy. Initially, real Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) system slant TEC (STEC) data were compared with dual-frequency GPS STEC, tomographic STEC, International Reference Ionosphere (IRI) model STEC and Global Ionospheric Map (GIM) STEC data for validation. For extended and large-scale statistical analysis of ionospheric TEC, the study compared tomographic VTEC with dual-frequency GPS VTEC, IRI model VTEC, and GIM VTEC, using dual-frequency GPS VTEC as a reference. Results from the comparison of four different datasets with DORIS data showed that, during gradual changes in ionospheric TEC, DORIS relative STEC data had mean root mean squared errors (RMSE) of around 1.3 TECU when compared to dual-frequency GPS relative STEC and tomographic relative STEC data. In contrast, the RMSE values with respect to IRI relative STEC and GIM relative STEC data were around 2 TECU and 2.3 TECU, respectively. Therefore, dual-frequency GPS STEC and tomographic STEC data were closer to DORIS STEC data compared to IRI model STEC data and GIM STEC data. The comparison results of three different datasets with dual-frequency GPS data showed that the maximum correlation coefficient between tomographic VTEC and dual-frequency GPS VTEC was 0.99, with a minimum RMSE of 1.39 TECU. In comparison, the maximum correlation coefficients for IRI model and GIM data were 0.87 and 0.97, with corresponding minimum RMSE values of 1.95 TECU and 3.50 TECU, respectively. Therefore, tomographic TEC accuracy in the Chinese region surpassed that of the IRI model and GIM data.