Acoustic and optical backscatter from flocculating sediments (FLOCSAM)

细悬浮粒子具有吸附金属和有机化合物等污染物的倾向，并对影响底栖生物群生长的光线的穿透起到屏障作用，因此对河口和沿海海域的水质产生深远影响；它们对敏感的海洋生态系统产生影响，影响养分循环，并对港口周围的疏浚和倾倒活动产生相当大的社会经济影响，因为泥沙会因沉降加剧而絮凝。因此，海洋科学家、工程师和管理人员需要能够测量细微的沉积物通量，以评估它们对沿海环境的影响。然而，细小的悬浮颗粒很少以其原始状态存在，而是形成絮凝体，这些絮凝体通常是矿物颗粒，生物碎屑，细菌和有机物的聚集，非均质组合。光学和声学仪器用于测量悬浮沉积物质量浓度，但几乎不了解絮凝对光和声音的影响。仪器是根据测量沉积物质量浓度的水样“校准”的。我们打算研究这个长期存在且具有科学挑战性的问题，即声音和光如何响应泥泞的沉积物，并通过理论和实验开发能够定量反演粘性沉积物的后向散射信号的算法，以预测质量浓度，结合光学和声学传感器的最佳特性。研究的理论结果将通过精心控制的小规模（库埃式水槽）和中型（水槽）实验室实验进行测试和评估，在这些实验中，可以对絮凝过程施加一定程度的控制，并在泥泞的河口场地进行全面的实地活动。水槽和现场试验将使用各种声学（ABS， ADV和ADCP）和光学仪器（OBS， list -100和INSSEV）以及泵送采样，速度和湍流测量。INSSEV（为该项目升级）将特别有价值，允许处理单个絮凝体的数字图像并测量其下降速度。

Fine suspended particles exert a profound influence on water quality in estuaries and coastal seas through their propensity to adsorb contaminants such as metals and organic compounds and by acting as a barrier to the penetration of light affecting growth of benthic biota; they impact on sensitive marine ecosystems and influence nutrient cycling and have considerable socio-economic impacts related to dredging and dumping activities around ports and harbours as sediment flocculates due to enhanced settling. Marine scientists, engineers and managers therefore need to be able to measure fine sediment fluxes to assess their impact on the coastal environment. However, fine suspended particles rarely exist in their primary state but form flocs which are typically aggregated, heterogeneous assemblages of mineral grains, biogenic debris, bacteria and organic material. Optical and acoustic instruments are used to measure suspended sediment mass concentrations but with almost no understanding of the effects that flocculation has on the light and sound. Instruments are 'calibrated' against water samples from which sediment mass concentration is measured. We intend to investigate this long-standing and scientifically-challenging problem of how sound and light respond to muddy sediments and develop, through both theory and experiment, algorithms capable of quantitatively inverting backscatter signals from cohesive sediment to predict mass concentration, combining the best features of optical and acoustic sensors. The theoretical results of the study will be tested and evaluated using carefully controlled small-scale (Couette-type tank) and medium-scale (flume) laboratory experiments where a degree of control can be exerted on the flocculation processes, and against a full-scale field campaign at a muddy estuarine site. Both the flume and field trials will use a variety of acoustic (ABS, ADV and ADCP) and optical instruments (OBS, LISST-100 and INSSEV) together with pumped-sampling, velocity and turbulence measurements. The INSSEV (up-graded for this project) will be especially valuable, allowing digital images of individual flocs to be processed and their fall velocity measured.