Temporal coherence and time spread of ocean surface scattered high frequency acoustic signals

Abstract

The influence of the ocean environment on the temporal coherence and time spread of high frequency, surface scattered and fully refracted acoustic signals over intervals ranging from a few seconds to tens of hours have been investigated experimentally. Acoustic data were collected during the broadband coherence experiment conducted in July 2002 off the coast of San Diego in a water depth of 1000 m. Signals transmitted include short pure tone pulses and broadband (up to 22 kHz) linear frequency modulated (LFM) sweeps centered at 20, 40, and 60 kHz. The projectors were suspended at two depths from a moored buoy at two different ranges. The receiver hydrophones were suspended from a subsurface float at depths from 40 m to 300 m. Environmental measurements included a towed CTD string, water temperature at a fixed point, near surface bubble layer using a multibeam sonar, current speed and direction, directional wave height, and wind speed. [Work supported by ONR Code 321US under the ARL Program.]