Abstract:

Thirty-second duration 250- to 375-Hz LFM pulses were transmitted from a towed acoustic transducer to study the effects of internal waves and the sea bottom on an acoustic signal propagating along a 30-km transmission path. The data were taken on the New Jersey continental shelf as a part of the multi-institutional SWARM95 experiment. Environmental data were collected by using CTDs, thermistor strings, a high-frequency acoustic flow visualization system, and a chirp sonar system. Geoacoustic properties of the bottom were inverted from the chirp sonar data with a 1.5-m vertical resolution and 40-m penetration. A deterministic sound speed field in the water column was constructed by imposing the high-frequency visualization measurements on both CTD and thermistor string data. Environmental data indicated that two distinct geological provinces and two major internal wave packets were crossed during the 30-km towed transmission. Using a full-wave broadband PE model, vertical structures of sound field were calculated for comparison to data obtained by a 32-element vertical line receiver array. Preliminary model/data comparisons indicate the dominance of water column effects over the bottom effects. [Work supported by ONR.]