Evaluation of excess phase and bending angle data from FengYun-3 radio occultation based on two independent processing chains

Abstract With long-term mission planning extending well into the next decade, the Chinese FengYun-3 (FY-3) meteorological satellite series acts as an important backbone for the provision of radio occultation (RO) data for climate science and numerical weather prediction (NWP). Independent evaluation is an essential part for considerate application of the data. Here we present results of the first cross-evaluation of RO low-level data, obtained by the GNSS occultation sounder (GNOS) onboard of FY-3 satellites, from two independent processing chains (Wegener Center, Graz; National Space Science Center–National Satellite Meteorological Center, Beijing). We analyzed and compared the orbit solutions, atmospheric excess phase, and bending angle profiles, for 3-month evaluation periods of FY-3C and FY-3D data in 2014 (FY-3C only) and 2019. We found the orbit data to be within requirements for high-quality RO data processing. Cross-comparison at excess phase level as well showed high-quality consistency overall, while some differences were revealed in the closed-loop to open-loop transition of FY-3D data. The cross-evaluation of bending angle profiles against European Centre for Medium-Range Weather Forecasts (ECMWF) forecast data also showed good agreement and adequate quality in general, while some distinct deviations occurred below 26 km altitude in the early FY-3C rising event data in 2014. The results underscore the high basic quality of the GNOS data for applications in climate research and NWP. At the same time they valuably inform subsequent work to resolve remaining biases, improve current processing algorithms, and include data from FY-3E, FY-3F, and FY-3G satellites.