COHERENCE OF ACOUSTIC SCATTERING FROM A DYNAMIC ROUGH-SURFACE

Numerical studies of the angular and temporal coherence of rough-surface acoustic scattering are presented at kh = 12, 20, and 32, where k is the acoustic wave number and h is the root-mean-square surface height fluctuation. The computations are based on point-source illumination of a one-dimensional pressure-release Pierson-Moskowitz dynamic rough surface, and the Kirchhoff approximation. In the region near specular, for a source-location grazing angle of 20-degrees, the angular variation of the scattered field coherence is found to predominantly depend on the product of k and a fixed length scale. The computed results show only a mild dependence on kh. For the same geometry, the temporal variation of the scattered field coherence is found to depend predominantly on (g DELTAt/U)kh, where g is the acceleration of gravity, DELTAt is the time shift, and U is the wind speed. A general method for scaling the scattered field coherence in terms of k, DELTAt, U, and the angular separation of the field points is suggested based on the findings. The effects of wind direction and surface-wave frequency cutoff on acoustic scattering are also noted.