Quasi-global soil moisture and freeze-thaw retrieval using Fengyun-3G GNSS-R observations

Fengyun-3G (FY-3G) is one of the satellites in the Fengyun series, equipped with a Global Navigation Satellite System-Reflectometry (GNSS-R) payload. FY-3G has been operating successfully for several months and has accumulated sufficient observations. To explore the land remote sensing potential of FY-3G GNSS-R observations, this study conducted surface soil moisture (SM) and freeze-thaw (F/T) state retrievals using FY-3G GNSS-R observations. The results show that the overall root mean square error (RMSE) and correlation (R) of the FY-3G SM retrievals compared to the contemporaneous Soil Moisture Active Passive (SMAP) SM are 0.056 cm3/cm3 and 0.91, respectively. The accuracy of the FY-3G F/T retrievals is 84.3%. In addition, independent stations similarly demonstrated the good performance of FY-3G observations for SM and F/T retrievals and showed that FY-3G and SMAP have comparable monitoring capabilities. This study successfully demonstrates the capability of FY-3G in SM and F/T monitoring. This will enlarge the range of the application of the Fengyun satellite for monitoring land parameters in the future.风云三号G星（Fengyun-3G, FY-3G）是风云系列卫星之一，搭载有全球导航卫星系统反射测量（Global Navigation Satellite System-Reflectometry, GNSS-R）载荷。FY-3G已成功在轨运行数月，积累了充足的观测数据。为探究FY-3G GNSS-R观测数据的陆地遥感应用潜力，本研究利用FY-3G GNSS-R观测数据开展了地表土壤湿度（surface soil moisture, SM）与冻融（freeze-thaw, F/T）状态反演工作。研究结果显示，FY-3G反演得到的土壤湿度与同期土壤湿度主动被动卫星（Soil Moisture Active Passive, SMAP）的土壤湿度数据相比，整体均方根误差（root mean square error, RMSE）与相关系数（correlation, R）分别为0.056 cm³/cm³与0.91。FY-3G冻融状态反演的准确率达84.3%。此外，独立站点验证结果同样证实，FY-3G观测数据在土壤湿度与冻融状态反演中表现优异，且FY-3G与SMAP的监测能力相当。本研究成功验证了FY-3G在土壤湿度与冻融状态监测领域的应用能力，未来将进一步拓展风云卫星在陆地参数监测方面的应用范畴。