The three-dimensional ionospheric tomography in Japan by using the adaptive Kalman Filter algorithm

  The three-dimensional (3-D) tomographic inversion is a crucial technique for imaging the ionospheric electron distributions (IEDs) on both the horizontal and vertical directions based on the total electron content (TEC) data. In this study, a regional 3-D tomography was realized in Japan using the Kalman Filter (KF) algorithm. In addition, to deduce the divergences, the adaptive Sage-Husa KF (SHKF) was proposed to determine the unknown priori information of the noise covariance encountered in the conventional KF (CKF). From this base, slant TEC (STEC) data observed by 55 GPS (Global Positioning System) receivers in the years of 2013 and 2018 was selected for IED reconstructions with the resolution 1º×1º×30 km in latitude, longitude and altitude, respectively. As for the ionospheric diurnal and annual variations, by comparing the F2 layer peak electron density (NmF2) simulated by SHKF, CKF, and the International Reference Ionosphere (IRI) model with the observed values detected by 4 Japanese ionosondes (Okinawa, Yamagawa, Kokubunji, and Wakkanai) during April 3-9, 2018 and 2013, the Root-Mean-Square-Error (RMSE) and co-releation index (ρ) were adopted to evaluate the simulated effciency. Results showed that the least RMSE (0.3084 in 2018, 0.5397 in 2013) and the best ρ values (0.9517 in 2018, 0.9896 in 2013) were both given by the SHKF-CIT method. Then, seasonal characteristics were implemented on January 02, March 20, June 14 and September 24, 2018, where the variations of northern EIA, winter and semiannual anomalies were accurately captured by the SHFK method. Meanwhile, the recalculated TEC values as well as the inverted vertical profiles manifested that SHKF-based tomography was outperformed the other methods. In the end, taking a strong geomagnetic storm happened on 26 August, 2018 as an example, both the meridional and latitudinal (along 135°E and 35°N, respectively) IEDs displayed more significant promotions than IRI model, and the results indicates that the IED around Japan developed by SHKF-based tomography is promising for the ionospheric studies and practical applications.