Abstract
Scattering from the sea surface was studied using a displacement hydrophone in order to observe the effect of surface-wave shadowing. The displacement hydrophone, able to receive the acoustic field at or near the sea surface, is particularly suitable for observing the effect of shadowing. A stable platform at sea was provided by the use of the NUWC Oceanographic Tower off San Diego. Comparison of preliminary results with Wagner's geometrical shadowing function indicates that the observed shadowing is less than would be expected theoretically. For example, with a wind speed of 20 kt the surface appears acoustically to be only 20% shadowed at 4° grazing angle, whereas geometrically 40% would be in shadow. This suggests that corrections to the scattering function using the geometrical approximation to shadowing may not be applicable. [The author received support under the Advanced Study Program from Naval Undersea Warfare Centers, San Diego, California.]
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