Transmission loss tomography of littoral hydrodynamics.

Abstract

Experiments of transmission loss tomography for turbulent and Reynolds stress structures were carried out in Kanmom strait using eight 5.5 kHz source-receiver pairs. The fluid motion within the turbulent current scatters the acoustic wave. The scattered acoustic waves radiate, experience losses due to attenuation and spreading, and are recorded in the form of transmission loss. Because they are small, surface and bottom losses are neglected leaving turbulent scattering and geometric spreading as the dominant transmission losses. Therefore, accurate measurement of transmission loss extracts the scattered acoustic energy losses. Total transmission loss minus spreading loss yields transmission loss (of scattered energy). Transmission loss yields turbulent current motions with the aid of the hydro-acoustics-invariant. From the fluctuations of turbulence on the orthogonal axes, the Reynolds stress tensors are calculated. Reynolds stresses make it possible to calculate the rip currents, upwelling, surf beat, wave surge, sediment transport, and all the elements of littoral hydrodynamics. The imaging of hydrodynamic elements using transmission loss alone is done for the first time.