Rufenach, C., 1995: A new relationship between radar cross-section and ocean surface wind speed using ERS-1 scatterometer and buoy measurements. Inter. J. Rem. Sens., 16, 3629-3647.
The ERS-1 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 ± 25 km of the scatterometer cells. These collocated measurements result in over 75000 matches in two different oceanic regions. The buoys measure hourly mean wind speeds from 0.2-10 m s-1 and 0.2-18 m s-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 0 dB/m s-1 at high wind speeds U=18 m s-1 and small incidence angles θ=20° to about 1.3 dB/m s-1 at low wind speeds U=3 m s-1 and large incidence angles, θ=55°. The CMOD4 model significantly underestimates the radar cross section measurements for U < ~3 m s-1 whereas the exponential model exhibits less bias.