Abstract:

An experiment was performed in the Spring of 1997 off the pier at the Scripps Institute of Oceanography. The objective was to measure the near-shore properties of bubble fields. A major component of the experiment was the Delta frame designed at NRL-SSC. The triangular frame, 9.4 m on each side, supported two sources and eight hydrophones. Measurements of acoustic travel time and attenuation were made at eight frequencies between 39 and 244 kHz. Details of the measurement apparatus will be presented elsewhere at this meeting [J. W. Caruthers et al., ``Observations of attenuation during the Scripps Pier bubble experiment'']. In this paper, a tomography algorithm [D. Rouseff and F. S. Henyey, J. Acoust. Soc. Am. 101, 3032 (1997)] is applied to a sampling of the data to produce cross-sectional mappings of attenuation. The bubble concentrations are shown to be inhomogeneous and carried across the frame by rip currents. Possible improvements to the tomography algorithm for imaging strongly attenuating structures are discussed. [Work supported by ONR.]