ASA 126th Meeting Denver 1993 October 4-8

3pUW1. Ambient noise in shallow seas: Propagation issues.

Ira Dyer

Dept. of Ocean Eng., MIT, 77 Massachusetts Ave., Cambridge, MA 02139

Whatever the source of ambient noise in a shallow sea, propagation to a distant receiver shapes in a major way its spectral character, its temporal properties, and its coherence or spatial distribution functions. Any one ambient noise mechanism is generally an incoherent superposition of a large number of similar elemental sources. Thus propagation modeling for ambient noise must address the multiple source question, and as well the modeling can take advantage of simplifications often afforded by multiple path averaging. In this context, the main confounding elements of shallow sea propagation including, but not limited to, downward refraction, sloping bottoms, sediment interaction, rough bottom scattering, and water column fluctuations are reviewed. In such complicated propagation channels the noise is modified in important detail, although much of its character remains broadly recognizable.