Advances in extracting current profiles from X-band radar images with a focus on retrieving subsurface current

X-band radar images of ocean waves offer a promising approach to estimate vertical current shear near the ocean surface, a region where direct measurement remains challenging. Inversion techniques on wavelength-dependent Doppler shifts have been used previously. However, they were restricted to a few meters below the sea surface. This study uses a smoothing technique along with in-situ measurements at lower depths to infer the current profile up to the mean sea level ( z = 0 m), thus delivering a measure for vertical current shear, an important indicator for the air-sea energy transfer. The method was applied to radar images collected during a storm event where concurrent measurements of an ADCP were available. The method also performs well without the use of in-situ measurements at lower depths, though accuracy improves when such data is available to stabilize the solution. This study has used shear as an overall measure of energy transfer of the wind into the water. Hence, a comparison of the extracted shear magnitude with the wind speeds at 10 m above sea level has been conducted. The shear magnitude increases are mirrored by the wind speeds. These promising results display that the study is a proof-of-concept study which requires future investigation. • Retrieval of current profile with the boundary layer just underneath the sea surface. • Current inversion from X-band radar images. • Improved results by incorporating in-situ measurements at lower depths. • Magnitude and direction of extracted shear follow pattern of wind measurements.