Evaluation and deep learning-based calibration of nearshore sea surface wind speeds from FY-3E GNOS-Ⅱ and Tianmu-1 missions

This study evaluates and calibrates wind products derived from Global Navigation Satellite System Reflectometry (GNSS-R) using data from the FengYun-3E (FY-3E) global navigation satellite system occultation sounder Ⅱ (GNOS-Ⅱ) and Tianmu-1 missions. The research highlights the significance of remote sensing for the accurate measurement of sea surface wind speeds in nearshore areas, which are crucial for environmental monitoring and climate studies. Initial comparisons with National Data Buoy Center (NDBC) measurements revealed root – mean – square errors (RMSE) of 2.49 m/s for FY-3E GNOS-Ⅱ Beidou navigation satellite system (BDS) signals and 2.13 m/s for global positioning system (GPS) signals. For the Tianmu-1 mission, the RMSE values were 3.21 m/s for BDS, 3.13 m/s for GPS, 2.91 m/s for GLONASS (GLO), and 2.91 m/s for Galileo (GAL) signals. To improve accuracy, especially in the complex nearshore environments, a deep learning calibration model incorporating residual blocks was employed. This model significantly enhanced the performance compared to a basic neural network. An ablation study confirmed that including residual blocks reduced RMSE by over 20% across all signal types. The calibrated model achieved substantial accuracy improvements in the test set, reducing RMSE to 1.03 m/s for FY BDS (improvement of 60%), 0.99 m/s for FY GPS (improvement of 54%), 1.57 m/s (improvement of 51%), 1.36 m/s for Tianmu-1 GPS (57% improvement), 1.26 m/s for Tianmu-1 GLO (improvement of 56%), and 1.50 m/s for Tianmu-1 GAL (improvement 47%).