Inferring the Vertical Turbulent Diffusion Coefficient from Backscatter Measurements with a Multibeam Sonar

Abstract

A 240 kHz multibeam sonar was deployed on a sub‐surface mooring in order to collect acousticbackscatter measurements from the bubbles in a ships wake in August, 2002. The sonar was located at a depth of 30 m and oriented so that its swath of beams was orthogonal to the shipstrack. Measurements proportional to the acoustic scattering cross‐section per unit volume were made and used to estimate the vertical turbulent diffusion coefficient in the ships wake using the same methodology that Thorpe used with a single‐beam echosounder underneath breakingwaves [J. Phys. Ocean. 14, 855–863 (1984)]. The wake was viewed as a distributed source of bubbles that are transported downward from the surface by turbulence. A steady state representation of the bubble field was used, where it was assumed that the bubble population exponentially decayed with depth, and that a bubble conservation equation could be written that only accounted for turbulent diffusion, buoyancy, and gas dissolution. Estimates of the verticalturbulent diffusion coefficient in the wake of a research vessel will be presented. [Work supported by ONR Code 321US. First author supported by a National Defense Science and Engineering Graduate Fellowhip.]

Department

Center for Coastal and Ocean Mapping

Publication Date

2003

Volume

114, Issue 4

Journal Title

Journal of the Acoustical Society of America

Pages

2300

Publisher

Acoustical Society of America

Digital Object Identifier (DOI)

10.1121/1.4809196

Document Type

Journal Article

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