A Study of Acoustic Characteristics in Suspended Sediment for Various Concentrations

Abstract

High concentration suspended sediment generated in coastal water and estuarine causes many social and environmental problems. It was reported that a high concentration aqueous suspension, composed of fine grained sediment particles, may hinder navigation and target detection, as well as contribute to deteriorating water quality. Therefore, this environment is currently being studied using acoustic instrument for high spatial and temporal resolution by many scientists. However, sound propagating through highly concentrated suspended sediment layers suffers severe attenuation; thus, it is important to examine the attenuation properties of suspended sediment for precise measurements. In this study, sound attenuation in suspended sediment was investigated using two sets of laboratory experimental data. First, a 5-MHz acoustic backscattering strength data as a function of suspended sediment concentration was used to verify the effect of the sediment attenuation when using ultrasound. Second, the sediment attenuation was measured using 0.5, 3, 5, and 7.5 MHz acoustic sensors and three sediment samples which have different particle size distributions. Subsequently, the particle size distributions of each sample were inversely estimated through a comparison between the measured data and model predictions. Our results show that the acoustic attenuation is very useful for estimating the particle size distribution in suspensions.