The results from acoustic scattering measurements conducted in the North Sea during the Synthetic Aperture Radar and X Band Ocean Nonlinearities (SAXON)-Forschungsplattform Nordsee (FPN) experiment are presented. Scattering strength values were obtained for selected frequencies (5--70 kHz) and for wind speeds up to 20 m/s. The grazing angle dependence was measured for 50 kHz at three different sea state conditions. Two grazing angle regimes were identified (above and below 60¿) where the wind speed dependence of acoustic backscattering shows a different behavior. One grazing angle from each regime (normal incidence and 45¿) was investigated to explain the physical processes that dominate the backscattering in the different wind speed regimes. In the low grazing angle regime the backscattering strength is caused by the small-scale surface roughness at low wind speeds and by subsurface bubbles at high wind speeds. There is only weak dependence of backscattering in the intermediate wind speed regime. Scattering and absorption of a random swarm of interacting bubbles inside the propagation range lead to undefined acoustic intensities in front of the surface. Thus scattering from a boundary layer instead of sea surface backscattering has to be considered. The presented acoustic data set is a base for further correlation with radar measurements that were conducted simultaneously. Good correlation between electromagnetic and acoustic backscattering is expected for the wind speed regime in which the scattering mechanisms are the same. ¿ American Geophysical Union 1995