Acoustic and optical backscatter from flocculating sediments (FLOCSAM)

微细悬浮颗粒对河口和沿海海域的水质产生深远影响，因为它们倾向于吸附金属和有机化合物等污染物，并对影响底栖生物群生长的光线的穿透起到阻挡作用；它们影响敏感的海洋生态系统，影响营养循环，并对港口和港口周围的疏浚和倾倒活动产生相当大的社会经济影响，因为沉淀物增加而形成絮状。因此，海洋科学家、工程师和管理人员需要能够测量细小的沉积物通量，以评估其对沿海环境的影响。然而，细小的悬浮颗粒很少以其原生状态存在，而是形成絮体，这些絮体通常是矿物颗粒、生物碎片、细菌和有机物质的聚集、异质组合。声学和光学仪器被用来测量悬浮泥沙的质量浓度，但我们对声音如何与复杂的絮体相互作用知之甚少。声学多普勒水流剖面仪(ADCPs)等仪器经常被用来“测量”细小物质通过水柱的通量，它们通常是根据测量沉积物质量浓度的水样进行“校准”的。我们打算研究这一长期存在的、具有科学挑战性的问题，即声音如何响应泥质沉积物，并通过理论和实验相结合的方式，开发能够定量反演粘性沉积物的声波后向散射信号以预测质量浓度的算法，并将这些与光学传感器的最佳特性相结合。这项研究的理论部分将建立在非粘性沉积物(沙)的后向散射模型的现有经验的基础上，并将根据储罐、水槽和现场结果来了解发展情况。将进行小规模(Couette类型的水池)和中型(水槽)实验室实验，其中可以使用简单的粘土悬浮液(没有沉积物或生物成分混合物的复杂性)对絮凝过程施加一定程度的控制，并最终在泥泞的河口地点进行全面的实地活动。实验室和现场试验将使用各种声学(ABS、ADV和ADCP)和光学仪器(OBS、LISST-100和成像技术)，以及抽水采样、速度和湍流测量。成像技术将建立在INSSEV计划的基础上，将特别有价值，允许处理单个絮团的数字图像并测量它们的下落速度。

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. Acoustic and optical instruments are used to measure suspended sediment mass concentrations but we have very little understanding of how sound in particular interacts with complex flocs. Instruments such as Acoustic Doppler Current Profilers (ADCPs), which are frequently used to 'measure' fluxes of fine material through the water column, are usually '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 responds to muddy sediments and develop, through a combination of theory and experiment, algorithms capable of quantitatively inverting acoustic backscatter signals from cohesive sediment to predict mass concentration, and to combining these with the best features of optical sensors. The theoretical component of this study will build on the existing experience with backscatter models from non-cohesive sediment (sand) and developments will be informed by the tank, flume and field results. Small-scale (Couette-type tank) and medium-scale (flume) laboratory experiments will be conducted, where a degree of control can be exerted on the flocculation processes using simple clay suspensions (without the complexity of mixtures of sediments or of biological components) and culminating in a full-scale field campaign at a muddy estuarine site. Both the laboratory and field trials will use a variety of acoustic (ABS, ADV and ADCP) and optical instruments (OBS, LISST-100 and imaging-technology) together with pumped-sampling, velocity and turbulence measurements. The imaging technology will build on the INSSEV programme and will be especially valuable, allowing digital images of individual flocs to be processed and their fall velocity measured.