The Accuracy Assessment and Scientific Research Progress of Ionospheric Radio Occultation Products Observed by Fengyun-3 GNOS

Global navigation satellite system (GNSS) radio occultation (RO) is a novel detection technique that can provide global ionospheric products with high vertical resolution, high precision, and low cost. In recent years, China has launched the Fengyun-3(FY3) series of meteorological satellites carrying the first RO payload to simultaneously receive global positioning system (GPS) and BeiDou navigation system (BDS) signals. In the accuracy assessment of RO products observed by GNSS occultation sounder (GNOS), the maximum F2-layer electron density (NmF2) of GPS occultation and BDS occultation has a standard deviation (std) of less than 20% in comparison with that of ionosondes. The std of F-layer worst case ionospheric scintillation index (
$S4_{\text{max}}^F$
) between Constellation Observing System for Meteorology, Ionosphere, and Climate and FY3/GNOS is less than 0.1. The above results prove the high precision of FY3 ionospheric RO products. The RO products have been applied to preliminary scientific research and applications, e.g., the process of main phase and recovery phase of magnetic storms revealed by the NmF2 observed by FY3C/GNOS, the premidnight dynamics of F-layer strong scintillation during magnetic storms revealed by GNOS scintillation data, the ionospheric perturbation driven by Tonga volcano eruption revealed by FY3/GNOS, applications of the RO data for the research of sporadic E layers, evaluation of International Reference Ionosphere model in statistics and ionospheric climatological characteristics, etc. With the successive network observation and continuous deployment of FY3 meteorological satellites, the continuous improvement of GNOS payload and the BDS system, massive high-precision ionospheric RO products will be developed and show more significant value.