Acoustic measurements of suspended sediments in the laboratory and at sea

Abstract

The application of acoustics for measuring suspended sediment transport processes potentially offers the opportunity for examining suspensions with a spatial and temporal resolution sufficient to probe turbulent and within wave sediment mechanisms. This should provide a significant advance in the understanding of the coupling between the fluid dynamics and the sediment response. Although acoustic backscattering devices have been employed by sedimentologists for over a decade to investigate marine suspensions, it is only relatively recently that a theoretical framework for interpreting the interaction of sound with marine suspensions has become available. In the present work a comparison is made between laboratory measurements of the backscattering and attenuation from a suspension and recent developments based on incoherent first-order multiple scattering. This analysis is also applied to acoustic data collected in an estuarine environment over sandwaves under turbulent tidal conditions. Acoustic estimates of the suspended concentration have been calculated and compared with independent tranditional measurements of the suspended concentration. The two observations of suspended sediments are shown to be in good agreement and this has provided confidence for calculating high spatial and temporal resolution estimates of suspended load. The latter display a highly variable concentration field and the relationship between this variability and turbulent structures is speculated upon. [Work supported by ARL:UT, NOARL, and MAFF UK.] a)On leave from the Proudman Oceanographic Laboratory, Merseyside L43 7RA, UK.