Intercomparison of ocean wind products from European C-band radars: ASCAT and Sentinel-1

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This letter assesses and compares the accuracy of the ocean wind vector products from two European C-band spaceborne radars: MetOp Advanced Scatterometer (ASCAT) and Sentinel-1A/B synthetic aperture radar (SAR) in Interferometric Wide (IW) mode. Two years SAR/ASCAT winds are collocated and validated against the buoys. To evaluate SAR/ASCAT winds against buoys in the same framework, we use 43 offshore buoy stations as common reference, and then validate them at comparable spatial resolution (25 km). Results show that ASCAT speed (direction) products exhibit higher accuracy with root mean square difference (RMSD) of 0.92 m/s (21.71°). Regarding the Sentinel-1 SAR, offshore wind speed (direction) data downsampled to 25 km present an RMSD of 1.03 m/s (27.48°), showing very little change compared to 1 km products originally provided by ESA. Furthermore, wind accuracy degrades for Sentinel-1 SAR at both 1 km and 25 km resolutions when validated against coastal buoys, where ASCAT winds are usually unavailable. In general, our results demonstrate that the Sentinel-1 winds are of lower quality than ASCAT in open ocean, and the performance of coastal SAR winds could be further improved. This finding could be helpful for better exploiting synergies in the ocean wind datasets from these two spaceborne radars.