This project aims at developing new and promising techniques based on acoustic Doppler technology for continuous estimation of important turbulence variables at ocean observatories. Addition of a 5th vertical beam (VADCP) allows estimates of all three components of turbulent kinetic energy as well as its dissipation rate. This project will assess their potential to provide time series measurements of turbulent as well as mean flow properties at remotely operated ocean observatories. The major technical challenges are provision of a stable platform, and sufficient power and data transmission for the fast sample rates needed to resolve the large-eddy structure of turbulent velocity fields. The major scientific challenges are the design of sampling protocols appropriate to the particular mix of processes generating turbulence at a given time, and the separation of surface wave and turbulent velocities. A final question is how to verify that the results are "correct", i.e., consistent with what is known of various forms of turbulence in the ocean. To address these sets of problems simultaneously, exploratory coastal deployments of a VADCP, in both wave-protected and wave-exposed locations, will be combined with development and use of a large-eddy simulation (LES) model suitable for the coastal ocean. LES velocity fields will be "sampled" with different VADCP protocols (choices of time/space resolution), and the results used to estimate the reliability with which turbulent quantities can be estimated from the 5-beam Doppler data under various combinations of turbulence forcing and surface wave contamination. In addition, the numerical results will be used to define requirements for statistical significance of future comparisons between time-continuous, spatially localized VADCP measurements, and time- and space-intermittent results from more traditional turbulence sensors carried on standard vertical profilers and/or autonomous vehicles. The observational results may in turn be used to examine the oceanic validity of assumptions underlying commonly used LES sub-grid parameterizations.
