Extraction of electron density profiles with geostationary satellite-based GPS side lobe occultation signals

Electron density profiles (EDP) obtained by GNSS radio occultation (RO) technique can improve the primary ionospheric parameters. However, current studies mainly focused on GNSS RO measurements observed by low Earth orbit satellites, which can only estimate EDP at low altitudes typically below 1000 km. We investigated the GPS RO measurements recorded on the geostationary earth orbit (GEO) satellite TJS-2 (telecommunication technology test satellite II). To improve EDP derivation precision, the total electron content derived from TJS-2 single-frequency excess phase is refined by a moving average filter, which can smooth high-frequency errors and indicate higher precision over the single-difference technique. By comparison with the ground-based digisonde, the IRI 2016 model and the Constellation Observing System for Meteorology, Ionosphere, and Climate satellite (COSMIC) EDPs, the TJS-2 ionospheric EDPs show good agreement with correlation coefficients exceeding 0.8. The TJS-2 average NmF2 differences compared to digisondes and COSMIC results are 12.9% and 1.4%, respectively, while the hmF2 differences are 1.65 km and 1.76 km, respectively. With a GEO satellite such as TJS-2, the side lobe GPS RO signals can also be received, and they are employed to estimate electron densities up to several thousand kilometers in height for the first time in this contribution. Our results also reveal that GEO-based RO signals can estimate EDPs at specific locations with daily repeatability, which makes it a very suitable technique for routinely monitoring EDP variations