Observation of small scale fluid processes in the vicinity of continental shelf breaks using high-frequency acoustic backscattering systems

Acoustic signal vertical and horizontal coherence properties are controlled on the shelf and near the shelf break by a variety of flow induced fluid processes. These processes perturb the sound speed field at spatial scales of a few hundred meters and less. The frequency of occurrence, depth distribution, and the relationship of the sound speed field variability to both oceanic and atmospheric fluid processes occurring on the continental shelf is poorly understood and are not generally included in most acoustic propagation models. Acoustic flow visualization records collected on the continental shelf and at the shelf break in water depths ranging from 50–300 m will be presented. These records will show: (1) the types of internal wave and smaller scale turbulence that occur in the summer and early fall in the vicinity of the New Jersey shelf; (2) some observation of the dissipation of large amplitude internal waves at the shelf break of the South China Sea; and (3) a variety of small scale instabilities that can perturb the sound speed field. [Work supported by the ONR Ocean Acoustic Program and ONRs NRL base funding.]