Coherence of high-frequency signals with emphasis on environmental effects

The relationship between the coherence of high-frequency, underwater acoustic signals and the upper ocean acoustic environment has been investigated experimentally. Acoustic and environmental measurements were made under ONR sponsorship (the ARL Program) during October–November 2000 at a site 30 miles off the coast of San Diego in water depths of 200 to 700 m. The transmitted signals consisted of 0.1- to 1.0-ms CW pulses and linear frequency modulated sweeps. Center frequencies of 18, 32 and 46 kHz and bandwidths from 500 Hz to 13 kHz were employed. The projector was suspended from the floating instrument platform (FLIP) at a water depth of 170 m while the receive hydrophones were suspended from a moored buoy at two different ranges of 640 and 2350 m with water depths of 200 and 700 m, respectively. Environmental measurements included water temperature, current speed and direction, directional wave height and wind speed. Temporal and spectral coherence are reported and compared with environmental patterns, theoretical predictions and prior research. [Work supported by ONR Code 321 (ARL Project).]