Acoustic and optical backscatter from flocculating sediments (FLOCSAM)

细悬浮颗粒物对河口和沿海的水质有着深远的影响，因为它们有吸附金属和有机化合物等污染物的倾向，并阻碍光线的穿透，影响海底生物群的生长;它们对敏感的海洋生态系统产生影响，影响养分循环，并具有相当大的社会效益，与港口周围的疏浚和倾倒活动有关的经济影响，因为沉积物因沉降加剧而絮凝。因此，海洋科学家、工程师和管理人员需要能够测量细沉积物通量，以评估其对沿海环境的影响。然而，细悬浮颗粒很少以其原始状态存在，而是形成絮凝物，絮凝物通常是矿物颗粒、生物碎屑、细菌和有机物质的聚集、异质组合。声学和光学仪器用于测量悬浮泥沙质量浓度，但我们对声音如何与复杂的絮凝体相互作用知之甚少。诸如声学多普勒海流剖面仪（ADCP）等仪器经常用于“测量”通过水柱的细物质通量，通常根据测量沉积物质量浓度的水样进行“校准”。我们打算调查这个长期存在的和科学上具有挑战性的问题，声音如何响应泥泞的沉积物和开发，通过理论和实验相结合，算法能够定量反演声学后向散射信号从粘性沉积物预测质量浓度，并结合这些与光学传感器的最佳功能。这项研究的理论部分将建立在现有的经验与后向散射模型从非粘性沉积物（砂）和发展将通知的坦克，水槽和现场结果。将进行小规模（库埃特型水槽）和中等规模（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）对絮凝过程进行一定程度的控制，并最终在泥泞的河口现场进行全面的实地活动。实验室和现场试验都将使用各种声学（ABS、ADV和ADCP）和光学仪器（OBS、LISST-100和成像技术），以及泵送取样、速度和湍流测量。成像技术将建立在国家科学研究所方案的基础上，将特别有价值，可以处理单个絮凝物的数字图像，并测量其下落速度。

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.