Multiantenna-Based Data Filling Method for Retrieving Electron Density Profiles From GNSS Radio Occultation Data

Retrieval of ionospheric electron density below low Earth orbit (LEO) altitude using global navigation satellite system radio occultation (RO) sounding requires total electron content (TEC) calibration by subtracting TEC on the non-occultation side from that on the occultation side. However, this calibration is not applicable to RO missions, where the occultation antennas cannot observe non-occultation side TEC. This article proposes a methodology for retrieving ionospheric electron density through multiantenna-based data filling. The non-occultation side TEC observed by using a precise orbit determination (POD) antenna data is connected to the occultation side TEC observed by an occultation antenna, enabling the application of the calibration technique. The methodology involves modeling TEC in the remaining gap between the data from POD and occultation antennas by utilizing the Epstein function with a varying scale height. The interior-point method is used to determine the optimal parameters for the function that best fits the observations. The proposed method is validated by applying it to Korean multipurpose satellite-5 (KOMPSAT-5) data and comparing the electron densities retrieved from KOMPSAT-5 data with collocated ionosonde observations. The results demonstrate that the electron density values retrieved by the proposed algorithm are in good agreement with those obtained from ionosonde measurements.