Czerski, Helen, Vagle, Svein, Farmer, David and Hall-Patch, Nick
Improvements to the methods used to measure bubble attenuation using an underwater acoustical resonator
Journal of the Acoustical Society of America, 130, (5), . (doi:10.1121/1.3569723). (PMID:22088016).
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Active acoustic techniques are commonly used to measure oceanic bubble size distributions, by inverting the bulk acoustical properties of the water (usually the attenuation) to infer the bubble population. Acoustical resonators have previously been used to determine attenuation over a wide range of frequencies (10–200 kHz) in a single measurement, corresponding to the simultaneous measurement of a wide range of bubble sizes (20–300 lm radii). However, there is now also considerable interest in acquiring measurements of bubbles with radii smaller than l6 micrometres, since these are thought to be important for ocean optics and as tracers for near-surface flow. To extend the bubble population measurement to smaller radii, it is necessary to extend the attenuation measurements to higher frequencies. Although the principles of resonator operation do not change as the frequency increases, the assumptions previously made during the spectral analysis may no longer be valid. In order to improve the methods used to calculate attenuation from acoustical resonator out-puts, a more complete analysis of the resonator operation is presented here than has been published previously. This approach allows for robust attenuation measurements over a much wider frequency range and enables accurate measurements from lower-quality spectral peaks.
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||This paper outlines a new theory to describe the output from acoustical resonators and to interpret that output accurately. Resonators are one of the few bubble measurements devices robust enough to use in the ocean for extended periods of time, while still providing the level of detail necessary for ocean studies. Bubbles in the ocean are crucial components of the air-ocean system, driving gas flux and aerosol production, but are still poorly understood. This significant improvement to resonator bubble measurements will enable more detailed oceanic studies of air-ocean interactions, which is a topic prioritized by NERC.
||27 Apr 2011 13:57
||18 Apr 2017 02:25
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