A new relationship between radar cross-section and ocean surface wind speed using ERS-t scatterometer and buoy measurements

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Abstract
The ERS–I spacecraft scatterometer, C-band VV polarization, acquired radar cross-section measurements over the global oceans during 1992 and 1993. We investigate the cross-section dependence on mean wind speed U using collocated buoys within ±25km of the scatterometer cells. These collocated measurements result in over 75000 matches in two diITerent oceanic regions. The buoys measure hourly mean wind speeds from 0·2–10 mS 1 and 0·2–18ms -1 in the equatorial Pacific Ocean and at mid-latitudes off the North American coasts, respectively. We present experimental evidence for a new and compact exponential model dependence on wind speed. The previously used power–law form inadequately characterizes the cross-section measurements based on a single index over a large wind speed range. The cross-sectional slope varies from about zero dB/ms-1 at high wind speeds U=18ms -1 and small incidence angles 0=20° to about 1·3dB/ms -1 at low wind speeds U=3ms -1 and large incidence angles, 0=55°. The CMOD4 model significantly underestimates the radar cross section measurements for U≤3ms -1 whereas the exponential model exhibits less bias.

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