Bound waves and Bragg scattering in a wind-wave tank

We present optical and microwave measurements that show the presence of bou nd waves traveling at the speed of the dominant wave in a wind-wave tank. W e suggest that when these bound waves are much shorter than the dominant wa ves, they are preferentially located on the leeward face of the dominant wa ve and hence have a mean tilt. We hypothesize that the turbulence associate d with these bound waves suppresses freely propagating, wind-generated wave s where bound waves are present so that we may divide the rough water surfa ce into patches containing free and patches containing bound waves. This mo del is shown to account for the observed histograms of slope measured in th e tank and, at least qualitatively, for the observed decrease in the probab ility of finding bound waves with increasing wind speed. Furthermore, if we add these bound, tilted waves to the free waves of the standard Bragg/comp osite-surface scattering model for microwave scattering from rough water su rfaces, then the model can account for many otherwise unexplained features of the scattering. Principal among these features are the rapid decrease in polarization ratio and rapid increase in the first moment of the microwave Doppler spectrum with increasing wind speed when the antenna is directed u pwind, features that occur to a much lesser extent when the antenna looks d ownwind.