High-Frequency Acoustic Propagation in Shallow, Energetic, Highly-Salt-Stratified Environments

Abstract

LONG-TERM GOALSThe long term goal of this research is to measure and understand high-frequency, line-of-sight acoustic propagation in an estuarine environment characterized by strong tidal flow, often large salinity stratification, high shear, high dissipation rates of turbulent kinetic energy, shear instabilities, and increased water property variability. OBJECTIVESAcoustic propagation techniques provide a means for remote-sensing of the path-averaged statistical structure and motion of the intervening flow, providing information on the 2-dimensional characteristics of turbulence, microstructure, and advection. Estuaries provide an excellent environment to quantify stratified turbulence and its influence on acoustic propagation as a broad range of stratification and turbulence intensities are encountered within a single tidal cycle.The primary objective is to conduct high-frequency (120 kHz), line-of-sight acoustic propagation measurements from 29 October to 2 November, 2012 in the Connecticut (CT) River estuary. In addition, measurements of high-frequency broadband acoustic backscattering (30 -600 kHz), currents (using a 1.2 MHz ADCP), suspended sediment concentrations, fluorescence, and continuous conductivity, temperature, and depth (CTD) measurements will be performed in order to support the interpretation of the scintillation data. Secondary objectives include testing the validity of the existing theoretical framework for propagation of high-frequency sound through a highly turbulent medium,