Observing Turbulence with a Modified Acoustic Doppler Current Profiler

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Abstract
This paper describes hardware and software modifications to a commercial incoherent acoustic Doppler current profiler that allow it to be used as a survey tool for measurement of turbulent velocity fields associated with coastal flows. The unambiguous measurement of vertical velocity, which is the heart of the modified system, can be used to provide quantitative estimates of turbulent kinetic energy E, as well as the spatial scales at which it resides and the rate ϵ at which it is dissipated. Provided that beam velocities are recorded directly, estimates of Reynolds stresses made from paired slant beams can be corrected for errors due to interbeam differences in bias error. With addition of a towed CTD, a direct measurement of buoyancy flux can be made. Although discussed here for an incoherent Doppler used in vigorous coastal turbulence, recent advances in coded-pulse Doppler sonars should enable use of most of these techniques in the lower-signal environment of the deep ocean, if a sufficiently stable platform can be provided.

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