Typhoon Maximum Sustained Wind Estimation Using Combined GNSS-Reflectometry and Scatterometer (CoGREAT): Initial Results From GNOS-R and WindRAD on FengYun-3E

Global navigation satellite system-reflectometry (GNSS-R) is capable of typhoon wind speed (WS) detection, benefiting from its unique feature of L-band forward-scattered signal with frequent temporal revisits. However, the fluctuation and deviation in observations limit the performance. Conversely, the C-band scatterometer can provide stable observations with a larger width, while the backscattered signal tends to be saturated when WSs exceed 25 m/s, accompanying rain attenuation. The complementary advantages of GNSS-R and scatterometer offer a novel strategy for typhoon maximum sustained wind (MSW) estimation. This study first explores the potential of typhoon MSW estimation using data provided by the GNSS occultation sounder-reflectometry (GNOS-R) and Wind Radar (WindRAD) codeployed on China's polar-orbiting meteorological satellite FengYun-3E (FY-3E). A typhoon MSW estimation method using combined GNSS-reflectometry and scatterometer (CoGREAT) was proposed, considering the distance from the typhoon center, the WS, and the rain attenuation. The experimental results of five typhoon cases in the Western Pacific show that CoGREAT outperforms GNOS-R-only and WindRAD-only methods for various grades of typhoons, achieving an overall absolute bias of 2.77 m/s taking the typhoon best-track (BST) dataset as the reference. Removing GNOS-R or WindRAD observations in CoGREAT reduces accuracy by 0.86 or 3.39 m/s, respectively, but still outperforms single-source methods without weight factors. In addition, using the typhoon center information provided by FengYun-4B (FY-4B) further proves that the method can be extended to near-real-time MSW estimation. This study provides a valuable reference for similar observation modes.