OCEANIC BUBBLE POPULATION MEASUREMENTS USING A BUOY-DEPLOYED COMBINATION FREQUENCY TECHNIQUE

This paper presents the results of using a combination frequency acous tic technique to measure the near-surface bubble population in the ope n sea. The combination frequency technique monitors the appearance of sum-and-difference signals generated by the nonlinear interaction of t wo sound fields: one, a high-frequency signal, scatters geometrically from the bubble, and the other, of much lower frequency, is used to ex cite the bubble into resonant pulsation. The text details the calibrat ion of the apparatus necessary to relate the measured heights of the s um-and-difference terms to actual numbers of bubbles and describes the experimental procedure for the collection of the oceanic data. In tot al, six trials were performed over a one-day period, each comprising t en ''snapshots'' of the local bubble population at ten discrete radii. This data was augmented with simultaneous video, slide, and dictaphon e records of the state of the sea around the measurement position.