Acoustic measurements in shallow water using an ocean glider

Acoustic data was collected on a single hydrophone attached to a Webb Slocum glider deployed by Rutgers University during the Shallow Water Experiment (SW06) on the continental shelf off New Jersey. The geometry of the experiment provided for adequate recording of the 224 and 400 Hz WHOI tomography sources. The glider periodically surfaced for GPS fixes and data transfer via satellite phone. A synthetic aperture is created through coherent processing of the acoustic data as the glider traveled through the water. A number of issues including varying depth and nonsteady motion must be accounted for due to the trajectory of the glider. However, the glider provides a low-noise and low-speed platform, potentially enabling detection of low level signals. Initial results show that the phase of the tomography signals is linear as the glider traverses the sound field. An acoustic normal mode representation of the field provides the basis for processing of the data similar to Hankel transform approach of Frisk and Lynch [J. Acoust. Soc Am. 76, 205–216 (1984)] and Holmes, Carey, and Lynch [J. Acoust. Soc. Am. 119, 3346 (2006)]. Effects of spatial variations in sound speed are examined. [Work sponsored by the Office of Naval Research.]