WIND SPEED RETRIEVAL FROM SATELLITE-BORNE SYNTHETIC APERTURE RADAR IN JAPANESE COASTAL WATERS

Abstract

 Coastal wind speeds retrieved from Sentinel-1 synthetic aperture radar (SAR) was compared with in-situ data observed in five coastal waters to develop more reliable methods for offshore wind assessments. All SAR images was resampled with a resolution of 100 m and 500 m to reduce speckle noise. As a result, Biases and RMSEs of SAR retrieved wind speeds with the 500 m spatial resolution are -0.62 to 0.88 m/s and 1.31 to 1.75 m/s, respectively. Additionally, the SAR wind speeds with the 500 m spatial resolution have higher accuracies than those with the 100 m spatial resolution in all coastal waters. That is why the 500 m spatial resolution can reduce an effect of strong backscatters from artificial structures (e.g. observation masts, buoys and ships) in SAR images. It is also found that breaking waves, which often occur in shallow waters, lead to the strong backscatter in SAR images. Consequently, the SAR wind speed shows higher than the in-situ wind speed in such coastal waters though the effect of breaking waves does not appear when the wind speed is more than 12 m/s.