Enabling coastal ocean ADCP-based turbulence measurements from a moving platform.

Anthony Kirincich, Physical Oceanography,
Peter Traykovski, Applied Ocean Physics & Engineering



Assessing the turbulence present in coastal flows is critical to connecting the boundary layer and mixing processing processes that control the dynamics of the coastal ocean to the hydrographic and velocity structure easily observed by shipboard or AUV-based sampling. Recent work by Farrar et al (2011) has developed a wavenumber spectra methodology to make sustained observations of turbulent dissipation from durable, lowcost instrumentation mounted on moored platforms. However, existing instruments are unable to provide the high sampling and low noise levels needed to adapt the methodology to moving platforms such as a towed-bodies, CTDs or AUVs. While the hydrographic and coarse-resolution ADCP observations generally being made from moving platforms enable an understanding of the water column structure and dynamics present, the addition of the dissipation measurements possible with this method will allow turbulence dynamics to be considered at the same time, greatly increasing our ability to link the large scale structures present to the turbulent processes that control them.

This proposal seeks funds to adapt a new, WHOI-built ADCP system in order to build a single transducer pulse-to-pulse coherent ADCP. Using the multi-purpose, high-frequency electronics board and transducers recently-developed by WHOI engineers, the instrument will be able to measure at ping pair rates approaching 180Hz with reduced-noise ensemble averages at greater than 50 Hz, over a spatial range of 1.5 to 2 m. To our knowledge, this would be the only ADCP capable of delivering the sample rates, noise requirements, and processing flexibility required to adapt the wavenumber spectra method to instruments on moving platforms. The instrument will be tested during the field components of on-going projects and made available to interested WHOI users, a number of which have already been identified.