An Improved Ionospheric Tomography Method Based on Adaptive Estimation of the Plasmaspheric Electron Content

The slant total electron content (STEC) values of signal paths from global navigation satellite system satellites to observation stations are an important data source for voxel-based computerized ionosphere tomography (CIT). However, the height range of the satellite signal rays is much larger than that of the ionospheric-tomography region. Therefore, it is commonly using an empirical model to obtain a fixed proportional coefficient of the STEC of each ray that is outside the tomography region, and then eliminating the influence of the plasmasphere electron content (PEC) to CIT fixed proportional factor for the PEC (CIT-FPPEC); however, it has been found that this is unreasonable and can negatively affect the accuracy of CIT. Herein, we propose an improved CIT method based on adaptive estimation of the PEC (CIT-AEPEC). Numerical experiments were conducted using global positioning system observation data over Europe from May 8 to May 15, 2019, and the inversion results were compared with the electron density profiles from ionosonde data and in situ measurements of Swarm satellites. In contrast to the CIT method without removal of the PEC (CIT-STEC) and CIT-FPPEC, statistical analysis showed that the root-mean-square error (RMSE) values between the CIT-AEPEC and ionosonde observations were improved by 34.54% and 26.78%, and the RMSE values between the CIT-AEPEC and Swarm measurements were improved by 39.77% and 36.97%, respectively. Finally, CIT-AEPEC inversion results were used to detect ionospheric perturbations during two magnetic storms from May 8 May 15, 2019. The effects of negative ionospheric storms and daily variations were clearly visible in peak value maps of the ionospheric electron density (IED). These results reveal that the proposed method is a useful tool for research examining space weather.