The contributors of sound scattering in stratified flows

Abstract

It is generally assumed that marine biomass dominates the backscattering everywhere in the ocean. However, stratified flows form both aggregated and solitary scatterers whose scattering levels are close to those of biologicals. The present work deals with theoretical and laboratory study of scattering phenomena in stratified flows of different types and regimes. Microscale clusters, flat and curved discontinuities, and solitary vortex rings were modeled and examined with both monostatic and bistatic acoustic schemes. Simultaneously they were optically visualized and photographed to provide their direct identification and computation of spatial spectra, and to extract characteristic scales being responsible for scattering. The average scattering levels converted to dimensionless backscattering cross section are of the same order or above those obtained in field measurements. Theoretical study seeks to reveal the mechanisms producing acoustic contrasts and to examine temporal characteristics of scattering. The scattering dynamics essentially depends on whether salinity or temperature stratification dominates the condition under which the scattering inhomogeneities arise. Also, attached internal waves contribution to produce the scattering interfaces was theoretically and experimentally confirmed. Shadowgraphs of scattering structures followed by synchronous scattering profiles, spatial and temporal characteristics of scattering, data of theoretical modeling are presented.