PATH-AVERAGED TURBULENT DISSIPATION MEASUREMENTS USING HIGH-FREQUENCYACOUSTICAL SCINTILLATION ANALYSIS

The path-averaged turbulent kinetic energy dissipation (per unit mass) is estimated in a shallow tidal channel using acoustical scintillatio n analysis. The tidal current ensures that fully developed turbulence prevails. In order to make measurements of the turbulence parameters, a high-frequency (67-kHz) acoustic propagation experiment was conducte d. Our acoustic data is compared to the weak scattering theory of Tata rski assuming a Kolmogorov turbulence model and compared with availabl e oceanographic data. Analysis of log-amplitude, phase, and phase-diff erence spectra shows close agreement with the theory. Comparison of th e acoustic data with direct measurement of temperature and salinity fl uctuations using in situ sensors allows evaluation of the contribution of turbulent velocity fluctuations to the scintillation signal. The r esults show that turbulent velocity fluctuations are the dominant (sim ilar to 95%) component of the observed acoustic scintillation, leading to estimates of the path-averaged turbulent energy dissipation, which rises and falls with the tidal current (epsilon similar to 10(-7)-10( -5) m(2)s(-3)). A confirmation of the validity of the weak scattering theory together with the Kolmogorov turbulence model in this environme nt is given within the context of the scattering strength-refractive i ndex variance parameters (Gamma,X).