Characterization of ASCAT measurements based on buoy and QuikSCAT wind vector observations

The new scatterometer Advanced SCATterometer (ASCAT) onboard MetOp-A satellite provides surface wind speed and direction over global ocean with a spatial resolu- tion of 25 km square over two swaths of 550 km widths. The accuracy of ASCAT wind retrievals is determined through various comparisons with moored buoys. The comparisons indicate that the remotely sensed wind speeds and directions agree well with buoy data. The root-mean-squared differ- ences of the wind speed and direction are less than 1.72 m/s and 18 , respectively. At global scale, ASCAT winds are compared with surface winds derived from QuikSCAT scat- terometer. The results confirm the buoy analyses, especially for wind speed ranging between 3 m/s and 20 m/s. For higher wind conditions, ASCAT is biased low. The ASCAT under- estimation with respect to QuikSCAT winds is wind speed dependent. The comparisons based on the collocated scat- terometer data collected after 17 of October 2007 indicate that there are significant improvements compared to previ- ous periods.

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