Performance Validation of Sea Surface Wind Speed Retrieval Algorithms and Products From the Chinese Tianmu-1 Constellation GNSS-R: First Results on Comparison With Other Wind Speed Products

The Tianmu-1 constellation is mainly based on BeiDou/Global Navigation Satellite System radio occultation (GNSS-RO) and BeiDou/GNSS reflectometry (GNSS-R) remote sensing technology, which can simultaneously achieve integrated stereo detection of GNSS-RO and GNSS-R. It is the first commercial GNSS remote sensing detection constellation in the world to achieve integrated business detection of "land surface, ocean, three-dimensional atmosphere, and ionized environment." Furthermore, it is the first GNSS remote sensing detection constellation in China that is compatible with receiving the five major GNSS systems (i.e., global positioning system, BeiDou, Galileo, GLONASS, and Quasi-Zenith Satellite System). This study used Tianmu-1 GPS-R/BDS-R/GAL-R/GLO-R global wind speed data from July 2023 to December 2023, and used five datasets as evaluation data, including the ERA5 reanalysis, CYGNSS L2, SMOS, CCMP, and NDBC buoy wind speed products, to present the results of the mission's first evaluation of sea surface wind speed estimates. The results show that the Tianmu-1 retrieval wind speed has good consistency with the CYGNSS verification wind speed. When the wind speed range is 0-35 m/s, its minimum RMSE can reach 1.74 m/s. The RMSE of the Tianmu-1 retrieval wind speed and the other four verification wind speeds (ERA5, CCMP, SMOS_SCA, and SMOS_SCD) are 2.25, 2.33, 2.74, and 3.17 m/s, respectively. For the wind speed products of the four systems in the Tianmu-1 constellation, GAL showed the best accuracy results. In addition, a comparative verification was conducted with buoy wind speeds, the BDS system demonstrated the best accuracy results, with the RMSE of 1.97 m/s.