Abstract The majority of reported field studies, using acoustic backscattering, for the measurement of nearbed suspended sediment processes, have been focussed on field sites with sand size fractions and unimodal size distributions. However, in many sedimentary environments, and particularly for estuaries and rivers, sands and muds coexist in the bed sediment substrate, forming a size regime that is often bimodal in nature. To examine the interaction of sound in these more complex sedimentary environments a numerical study is presented based on observations of sediment size distributions measured in the Dee estuary, UK. The work explores the interpretation of the backscatter signal from a mixed sediment composition in suspension, with mud-sand fractions varying with height above the bed. Consideration is given to the acoustical scattering properties and the inversion of the backscatter signal to extract information on the suspension. In common with most field deployments, the scenarios presented here use local bed sediments for the acoustic inversion of the backscattered signal. The results indicate that in general it is expected that particle size and concentration will diverge from what is actually in suspension, with the former being overestimated and the latter underestimated.

中文翻译：

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混合砂泥层上方悬浮浓度和粒径的声散射特性和反演

摘要 大多数使用声学反向散射测量近床悬浮沉积物过程的现场研究报告都集中在具有砂粒级数和单峰粒径分布的现场。然而，在许多沉积环境中，特别是在河口和河流中，沙子和泥土共存于床层沉积物基质中，形成了一种通常是双峰的大小范围。为了检查声音在这些更复杂的沉积环境中的相互作用，根据在英国迪伊河口测量的沉积物尺寸分布的观察，提出了一项数值研究。这项工作探索了来自悬浮混合沉积物成分的反向散射信号的解释，泥沙比例随床层上方的高度而变化。考虑了声学散射特性和反向散射信号的反演，以提取有关悬浮液的信息。与大多数现场部署一样，这里介绍的场景使用本地床沉积物进行反向散射信号的声学反演。结果表明，一般而言，预计颗粒大小和浓度将与实际悬浮液不同，前者被高估，后者被低估。