COHERENCE OF ACOUSTIC SIGNALS RERADIATED FROM TIME-VARYING SURFACE OF OCEAN

The space and time variation of a monochromatic acoustic plane wave reradiated by the moving, rough surface of the ocean is described using coherence theory. The complex degree of coherence of the pressure field is calculated approximately for the extreme cases of slightly rough and very rough surfaces. For both of these cases, the results are specialized to the situation of a wind generated sea described by the Neumann Pierson directional wave spectrum, and the dependencies of the coherence upon surface roughness and the angles of incidence and observation are shown. For the case of a slightly rough surface, the reradiation is principally a reflection, and the coherence in the direction of specular reflection is the same as that for a smooth surface. Away from this direction, there is scattering, and the coherence depends upon the surface roughness. For very rough surfaces, there is diffuse scattering in all directions with no reflection, and the coherence depends upon the surface roughness for all angles of observation. © 1969, Acoustical Society of America. All rights reserved.