Acoustical probing for microbubbles at sea

Abstract

Free gas bubbles have been indicted for many physical processes at sea including: scavenging detritus and chemicals from the ocean volume; generating droplets whose salts affect thunderstorm activity over the sea; providing cavitation nuclei; producing sound scatter and sound attenuation. It is the latter two phenomena that make acoustic measurements the most promising pathway for conducting a census of bubble populations. In particular, the very large scattering and extinction cross sections of a bubble at resonance, and the dispersion of sound speed in bubbly water, have made it possible to recently obtain marine bubble populations as a function of radius from 20 to 300 microns at depths to 15 metres. The~rowing knowledge of bubble numbers and behaviour will, in turn, permit more accurate predictions of sound propagation and fluctuations, particularly near the sea surface.