ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

3aUW2. Acoustic pulse to pulse variability due to seawater temporal temperature fluctuations.

Li Zhang

Ctr. for Marine Sci., Univ. of Southern Mississippi, Stennis Space Center, MS 39529

Ralph Goodman

Penn State Univ., State College, PA 16804

Steve Stanic

Naval Res. Lab., Stennis Space Center, MS 39529

Mire and Stanic (preceding abstract) have observed significant pulse to pulse fluctuations in high-frequency seafloor backscattering measurements in which the sound sources and receivers were mounted on a tower that stood on the seafloor in a shallow-water environment (about 30 m). This paper presents the hypothesis that temperature fluctuations that are associated with turbulence can account for the acoustic variability. The model is based on a random distribution of fixed discrete scatters on the surface of the seafloor. Computations that sum the arrivals of scattered CW pulses for a range of changes in travel times that are due to varieties in the average temperature along the paths reveal fluctuations similar to Mire and Stanic's observations for a range of tens of meters, temperatures changes as small as a tenth of a degree Celsius, and frequencies of about 40 kHz and higher. Comparisons between computations and measurement are presented in this paper. [Work supported by NRL/Stennis.]