There exists a range of acoustic techniques for characterizing bubble populations within liquids. Each technique has limitations, and complete characterization of a population requires the sequential or simultaneous use of several, so that the limitations of each find compensation in the others. Here, nine techniques are deployed using one experimental rig, and compared to determine how accurately and rapidly they can characterize given bubble populations. These are, specifically ͑i͒ two stationary bubbles attached to a wire; and ͑ii͒ injected, rising bubbles.

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There are great benefits to sizing bubbles using a two frequency technique, which examines the appearance of sum-and-difference signals generated by the interaction between a resonant bubble pulsation and a much higher frequency imaging beam. This paper presents the results from using the technique to size bubbles in the ocean surf zone, and details the pulsation model used to calibrate the returned data such that the height of the bubble scattered signal can be related to the number of resonant bubbles of that size. It also shows how ambiguities and inaccuracies ͑brought on through turbulence and the substantial off-resonance nature of the signal͒ which affected earlier oceanic tests using the same method can be identified in the returned signal or removed from the estimate during the data processing.

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