THE USE OF A COMBINATION FREQUENCY TECHNIQUE TO MEASURE THE SURF ZONEBUBBLE POPULATION

There are great benefits to sizing bubbles using a two frequency techn ique, which examines the appearance of sum-and-difference signals gene rated by the interaction between a resonant bubble pulsation and a muc h higher frequency imaging beam. This paper presents the results from using the technique to size bubbles in the ocean surf zone, and detail s the pulsation model used to calibrate the returned data such that th e height of the bubble scattered signal can be related to the number o f resonant bubbles of that size. It also shows how ambiguities and ina ccuracies (brought on through turbulence and the substantial off-reson ance nature of the signal) which affected earlier oceanic tests using the same method can be identified in the returned signal or removed fr om the estimate during the data processing. (C) 1997 Acoustical Societ y of America.