SAR Doppler Measurements of Ocean Surface Velocities Over Tropical Cyclone Cases

Abstract Spaceborne synthetic aperture radar (SAR) has been widely used to observe tropical cyclone (TC) wind forcing on the sea surface. Beyond its capability to retrieve wind fields, SAR also provides a unique mapping of one‐dimensional sea surface velocity along the radar line‐of‐sight via the Doppler centroid anomaly. This study utilizes Sentinel‐1 acquisitions over two representative TC cases, Maria (2017) and Cimaron (2018), to examine the relationship between Doppler velocity and the SAR‐derived wind field. For Maria, the spatial distribution of closely follows the radial wind speed projected onto the radar line‐of‐sight , exhibiting a distinct quadrant asymmetry in this case. The ratio of to is approximately 8% in the front right quadrant but decreases to 4% in the rear left quadrant. This asymmetry is attributed to the influence of ocean swell, as supported by analytical model simulations. Following swell enhances wind‐driven surface velocity in the front quadrant, whereas opposing swell suppresses the wind‐induced motion in the rear. In the case of Cimaron, Doppler velocity effectively delineates the Kuroshio Current, a feature not detectable in radar backscattering observations. These two case studies emphasize the added value of SAR‐derived Doppler velocity as a complementary constraint on wind–wave–current interactions under extreme TC conditions. The results illustrate how SAR Doppler observations can inform interpretation of surface velocity variability under TC forcing, while broader generalization across storm events shall require statistical analysis of a larger data set.