Robert Bruce Williams
Code 7801 NRaD Div. NCCOSC, San Diego, CA 92152-5000
A method of boundary reverberation reduction for shallow water ducts has been devised that makes use of a vertical array of sound sources. By controlling the waveforms of the sources, control over the phase and amplitudes of a selected set of modes can be made. This in turn allows formation of nulls in the field at specified range/depth pairs. At a given range, the nulls are chosen to be on the bottom of the duct where, for low and mid frequencies, most of the scattering is generated. However, at that same range, maxima in the field at other depths are present, thus enhancing the echo-to-reverberation ratio for reflectors at certain depths in the water column. Presented is the formalism in terms of mode theory, and field calculations for several environments. [Work supported by ONT.]