First View of Synchronous Wave and Wind Retrieval from 1mC-SAR TOPW Image during Typhoons

Since 2024, China's 1mC synthetic aperture radar (1mC-SAR) constellation, operating in terrain observation by progressive scans (TOPSs) mode (40-m resolution and 600-km swath), has enabled daily typhoon observations over the western North Pacific. This study represents the first simultaneous retrieval of typhoon wind and wave parameters from 1mC-SAR observations. Unlike conventional methods relying on a low-signal-to-noise-ratio (SNR) vertical-horizontal (VH) polarized normalized radar cross section (NRCS), we develop a Transformer-based joint wind-wave retrieval framework for typhoon conditions. A dataset of over 800000 subscenes from 208 images of 28 typhoons during 2024-2025 was collocated with the reconstructed wind speed and regional ocean modeling system-simulating WAves nearshore (ROMS-SWAN) hindcast wave fields. The Transformer uses a total of 19 image-derived intensity and spectral features to retrieve significant wave height (SWH) and dominant wave period (DWP). For wind speed retrieval, the retrieved wave parameters are used as auxiliary inputs, and wind-wave growth constraints are embedded into the loss function. The Transformer outperforms a multilayer perceptron (MLP), a residual network (ResNet), and extreme gradient boosting (XGBoost), achieving improved retrieval accuracy for SWH (RMSE = 0.60 m, r = -0.96), DWP (RMSE = 1.23 s, r = 0.79), and wind speed against soil moisture active passive (SMAP) observations (RMSE = 2.50 m/s, r = 0.92). Translation-induced asymmetry analysis shows strong wind-wave coupling over the left and back flanks of Northern Hemisphere typhoons (r = 0.46 -0.71), whereas the right flank is weakly coupled with the back flank (r = 0.04-0.47). These results indicate that typhoon-generated waves exhibit more pronounced asymmetry than the wind field. Future work will focus on direct deep-learning-based retrieval of typhoon wave spectra from SAR imagery, which may further improve the understanding of complex sea states and wave propagation under extreme tropical cyclone (TC) conditions.