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Acoustic Measurements of Tiny Optically Active Bubbles in the Upper Ocean

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In this project, which is closely linked to a separate project where the goal is to measure wave induced bubble clouds and their effect on radiance in the upper ocean N000140710754, we intend to address the disturbing fact that despite the fundamental importance of optical backscatter in the ocean it is still not possible to explain more than 5 to 10 percent of the particulate backscattering in the ocean based on known constituents even during periods with no active wave breaking Terrill Lewis, 2004. One hypothesis is that very small bubbles that have been stabilized by surfactants may be responsible for part of the missing backscatter. The long-term goal of this project is to detect these small bubbles using acoustical techniques, investigate possible surfactants and their role in bubble dynamics, and determine the role of these bubbles on upper ocean radiance. The main objective is to improve on an existing instrument design to allow for in situ measurements of bubbles over a wide range of bubble radii from approximately 500 micrometer at the upper end and down to less than 3 micrometer. We are pushing the technology to its limit with a goal of reaching bubble radii as small as 1 micrometer. We now have three systems where we obtain data at frequencies as high as 1MHz, corresponding to a smaller bubble radius limit of 3 micrometer. These systems were incorporated into the RadyO Scripps Pier experiment in January 2008 and the experiment conducted in Santa Barbara channel during September 2008. After extensive modifications and improvements to the systems during the winter, spring and summer of 2008-2009 the systems were again successfully deployed from RP FLIP and RV Kilo Moana off Hawaii during September 2009.

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  • Physical and Dynamic Oceanography
  • Acoustics
  • Optics

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