Observation of Wind Direction Change on the Sea Surface Temperature Front Using High-Resolution Full Polarimetric SAR Data

Abstract

In this study, we derive high-resolution wind speeds and directions from full-polarization synthetic aperture radar (SAR) data. Previous wind retrieval result from conventional single-polarization SAR data has a limitation to resolve small-scale structures in the surface wind because external wind direction data with coarser spatial resolution than those of SARs have been commonly used as an input. Using fully polarimetric SAR data, however, both wind speed and direction can be derived with high resolution from the image itself without any ancillary data. We derive wind field off the southern coast of Korea from the Radarsat-2 quad-polarization data and investigate the spatial variation. The retrieved wind field from the Radarsat-2 image presents a detailed structure including small-scale variations which is unobtainable from conventional wind observations. Comparison of the derived wind directions with in-situ buoy wind measurements shows a small difference of 8 degrees which is regarded as sufficient to analyze small-scale wind vector changes. The retrieved wind field off the southern coast of Korea demonstrates the distinct patterns of direction changes. While blowing over the sea surface temperature (SST) frontal zone, the veering angles of wind vectors decrease and then are restored. The analysis of SAR-derived wind vectors with coinciding temperature distributions confirms that the variation in SAR-derived wind vectors on the SST fronts is mainly induced by the stability effect. This study also addresses the important role of precise wind direction retrieval on the accuracy of retrieved wind speed.