- Instrumentation for the Measurement of Bubble Size Distributions in the Ocean Surface Layer
This program was initiated to develop and test instrumentation for the measurement of entrained air and bubble size distributions in the ocean surface layer beneath breaking waves. Bubbles in the ocean surface layer play an important role in air-sea gas transfer, in the generation of aerosols, in biological processes, and in the acoustics of the surface layer. Furthermore, if laboratory data and preliminary field measurements are confirmed, then the air entrained by breaking waves may be dynamically significant through the work done against buoyancy forces.
Bubbles are also important as tracers for acoustic instruments including Doppler and imaging techniques which can be used to measure Langmuir circulations, surface waves and currents. As these techniques become more sophisticated there is a growing need to better understand the role of bubbles. The surface expression of subsurface bubbles is the whitecap, and although a number of studies of whitecap coverage have been undertaken, there is no data on the relationship between whitecap coverage and subsurface bubble size distributions. Building on our experience in measuring air entrainment by breaking in the laboratory and the field, and in the acoustics of breaking waves and the surface wave zone, this program focuses on developing a technique to measure and invert measurements of the sound speed and acoustic attenuation in the range 2-200 kHz, to give bubble size distributions in the (radius) range of approximately 15 – 1500 mm.