Scattering from suspended sediments having different and mixed mineralogical compositions: comparison of laboratory measurements and theoretical predictions

Abstract

Laboratory measurements of the acoustic scattering properties of aqueous suspensions of non-cohesive sands having different and mixed mineralogical compositions are presented. Four different types of sand are examined: quartz, crushed shell, magnetite, and muscovite mica. The experimental data obtained for each type of sand are compared with theoretical scattering predictions for spheres having the same physical properties. The results show that for each type of sand, scattering is enhanced in the geometric regime relative to the sphere predictions, and for mica, scattering in the Rayleigh regime is reduced. To provide a theoretical framework for the observations, the applicability of two different modified sphere scattering models previously reported in the literature is evaluated. Measurements of the ensemble scattering properties obtained from mixtures of the different sands are also presented and compared with theoretical predictions. The results show that to accurately predict the scattering properties of compositionally diverse mixed sediment suspensions, it is necessary to know the relative proportions of each mineral present at each size within the size distribution; however, the scattering properties can be approximated for the suspensions studied by considering only the dominant mineral by mass.