Acoustic Scattering from a Wind Driven Water Surface.

Abstract : A very substantial fraction of the effort was devoted to improving the experimental facility. A partly automated hydrophone positioning system was installed in order to facilitate measurement of scattered power for a variety of transmitter and receiver locations. Improved hydrophone amplifiers now furnish the required signal to noise ratios for reliable measurements with receiver placement varying all the way from the forward-scatter to the back-scatter postion. A greatly improved waveheight probe will permit characterization of surface statistics at a level of detail not previously accessible. Such a level of detail appears to be essential to any effort to reconcile experiment with theory. The construction process is now largely complete and measurements are in progress. The first azimuthal surveys of scattered power have been carried out and are included in this report. It is clear from this limited data set that some key features of the scattering process (e.g. back scattered power level) are poorly predicted by existing theory. A major portion of this report is therefore devoted to a review of theoretical background. The standard analytical approaches are examined to see what changes in the usual assumptions might lead to results more compatible with experimental observations.