Estuarine measurements of suspended sediments over sand waves have been taken with the objective of clarifying the role of turbulence in suspension transport, sand waves development, and migration. To discern the mechanisms of transport, observations of the turbulent flow were taken and records of the response of the suspended sediment concentration were obtained using acoustic backscattering (ABS). As an intermediate goal of the overall objective an analysis of the ABS data has been conducted with the aim of assessing and quantifying the acoustic technique. Recent theoretical descriptions of the interaction of sound with suspensions are presented, and predictions are compared with a laboratory study on suspensions of spheres and noncohesive sediments. The laboratory data show the theoretical approach to be broadly correct, and it has been implemented to interpret the estuarine observations. Acoustic estimates of the suspended sediment concentration have been compared with pumped sample data and shown to be similar. Comparison of the laboratory and estuarine estimates for the form function and total scattering cross section for the estuarine sediments is presented, and some unresolved differences are considered. The effects of the sediment attenuation and the random amplitude of the backscattered signal are also highlighted, and their implications regarding acoustic estimates of the suspended sediment concentration are addressed. Finally, after assessing the accuracy of the acoustic approach, high‐resolution estimates of the suspended concentration are presented with some speculation on the origins of the concentration variability observed.

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Increasingly in recent years the application of acoustic backscattering to the quantitative measurement of suspended sediment particle size and concentration at sea has gained acceptance. A number of works describing the interaction of sound with suspensions have been published, and the scattering properties of suspended sediments formulated. However, there have been relatively few experiments conducted in the marine environment, which have attempted to assess the accuracy of the acoustic measurements by direct comparison with in-situ samples, taken simultaneously with the acoustic observations. The purpose of the present work is to report on such an experiment, and to evaluate the accuracy of the acoustic technique. To this end multifrequency acoustic measurements of suspended sediment profiles were collected in an estuarine environment, subject to strong turbulent tidal currents, which generated high concentrations of suspended sediments. To obtain the sediment parameters from the acoustic data an inversion needs to be applied, and this inversion is examined here in some detail, particularly for the case when sediment attenuation is substantial. To assess the sediment parameters derived from the acoustic inversion, mean acoustic estimates of particle radius and concentration are compared with the benchmark of in-situ pumped sampling. In addition to the analysis of the mean data, high-resolution images of the suspension dynamics have been generated, and the validity of these observations appraised by evaluating the internal consistency of the multifrequency results.

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