A novel technique for measuring mixing using acoustic Doppler current profilers (ADCPs)

Vertical mixing in shelf seas and estuaries is an important process that dominates the transport of water properties (e.g. sediments or pollution) in the marine environment. Acoustic Doppler Current Profilers (ADCPs) have been widely used for both monitoring and research in shelf seas and estuaries. While the potential of ADCPs to measure velocity fields has been realised, recent advances in processing techniques have allowed insights into mixing processes throughout the water column. In this presentation we describe a structure function technique to estimate Turbulent Kinetic Energy dissipation rates (ε) that has previously been used in the atmospheric sciences and here has been applied to ADCPs. We have compared this with 2 established methods of estimating turbulent parameters in the water column: the ADCP variance method, which estimates the momentum transfer through the water column and the Fast Light Yo-yo (FLY) microstructure profiler which measures turbulent dissipation. The structure function method compares well with the FLY microstructure dissipations, with a ratio of structure function dissipation: FLY dissipation of 0.75.