Visualization and acoustic sounding of the fine structure of a stratified flow behind a vertical plate

High-resolution shadow visualization and high-frequency sonar detection are applied to separate out the density wake and a fine streaky structure in the vicinity of a vertical plate in motion in salt-stratified water. The length of the sounding acoustic wave is taken to be approximately equal to the universal microscale $delta _N^v = sqrt {{v mathord{left/ {vphantom {v N}} right. kern-0em} N}}$ , where ν and N are the kinematic viscosity and the buoyance frequency. In the spectra of the vertical oscillations of the acoustic contrast some characteristic frequencies ω are separated out and used to calculate the local Stokes microscales $delta _omega ^v = sqrt {{v mathord{left/ {vphantom {v omega }} right. kern-0em} omega }}$ in the density wake region. The scales determined from the data of independent optical and acoustic measurements are in agreement with each other.