Validation of SRTM-derived surface currents off the Dutch coast by numerical circulation model results

The feasibility of exploiting the along-track separation of 7 m between the two X band antennas of SRTM for ocean current measurements was already demonstrated by us at IGARSS 2002. We presented an SRTM image of the Dutch Waddenzee with clear phase variations in water-covered areas, which could be converted into line-of-sight current variations by about 1.3 m/s. A comparison with a current map from a tidal atlas showed good qualitative agreement, but digital reference data for a quantitative validation of the SRTM results were not available. In this work we present a detailed comparison of the SRTM data with simulated current fields from the numerical circulation model KUSTWAD. We obtain an overall correlation of 0.558, a regression coefficient of 1.011, and an rms difference between SRTM and KUSTWAD currents of 0.24 m/s. Furthermore, we analyze the correlation of spatial variations in the measured and simulated current fields on different length scales. We find that SRTM can resolve the current variations which are relevant to KUSTWAD down to scales on the order of 1 km.