Abstract:
The development of a broadband sound velocimeter allows the simultaneous measurement of sound speed and attenuation over a wide range of frequencies, providing insight into the dispersive characteristics of a bubbly medium. The velocimeter measures the dispersion of a broadband acoustic pulse containing power over frequencies ranging from 2 to 140 kHz across a fixed pathlength. The resulting data are inverted using a simple inversion scheme to arrive at bubble size distributions over a range of radii extending from 20 to 1600 (mu)m. A large wind wave channel located at the Hydraulics Laboratory-S.I.O. provides an ideal location for testing and calibration of the system. Filled with seawater, the channel can generate O(1 m) breaking waves, providing bubble size distributions similar to those found in the field. Results of the lab measurements and comparisons of inverted bubble size distributions with an independent optical bubble sizing technique will be discussed. Preliminary results of a near-shore deployment of the system will be presented, emphasizing results of the data inversions in context of previously reported bubble size distributions. [Work supported by NSF and ONR.]