Developing a Global Listening Network for Turbidity Currents and Seafloor Processes

我们的总体目标是通过开发和展示可形成广泛和长期监听网络的新型传感器系统，从根本上改变对海底过程和危害的理解。这些低成本和高能效的传感器包括水听器(水柱中的声学噪声)和地震检波器(地面震动)。数据将通过弹出式浮标和卫星链路返回，非常成功的ARGO项目开创了水柱剖面的先河。这种类型的低成本网络可能会有异常广泛的应用，如对宝贵的海底基础设施的威胁发出警告，监测CCS设施或天然气管道的泄漏，或海啸预警系统。在这里，我们旨在回答关于海底物质流(浑浊流和山体滑坡)是如何被触发，然后如何表现的基本问题。这些危险且往往威力巨大(2-20米/S)的海底事件形成了地球上最大的沉积物堆积、最深的峡谷和最长的航道系统。浑浊的水流可能持续数百至数千公里，破坏海底电缆网络，这些网络承载着全球95%的数据流量，包括互联网和金融市场，或战略石油和天然气管道。这些流动在有机碳和营养物质向深海的转移以及地球化学循环方面发挥着全球重要的作用；同时它们的矿藏在世界各地拥有宝贵的石油和天然气储量。众所周知，潜艇的物质流在行动中很难测量，而且与它们的空中近亲相比，测量的数据很少。这意味着，在对海底物质流如何触发、其频率和跳动以及它们的行为方式的基本理解上存在根本性的差距。最近的监测使用耗电(有源)传感器，如声学多普勒海流剖面仪(ADCP)取得了进展。但有源传感器有很大的缺点，不能在全球范围内部署。它们只能进行短期测量，位于锚定在这些强大水流中的系泊设备上(这通常会带走昂贵的系泊设备和传感器)，它们需要多个周期的昂贵考察船才能部署和找回。因此，我们将设计、制造和测试被动传感器，这些传感器可以以低得多的成本部署在广泛的地区。这些新型传感器将记录质量流量计时和触发；以及船头速度(从传输时间)和流量功率(通过声波或振动信号的强度)的变化。我们将首先确定水听器和地震检波器如何最好地记录海底质量流量，以及记录如何随流量速度和类型或与传感器的距离而变化。我们在三个地点的初步工作已经表明，水听器和地震检波器确实记录了质量流。在这里，我们将确定捕捉质量流信号的最佳方法，并将其与其他过程区分开来。这项工作将为设计新一代低成本(&lt；GB 5k)智能传感器奠定基础，这种传感器无需昂贵的水面船只即可通过弹出式浮标和卫星链路返回数据。技术的进步使这一项目变得及时，因为它们允许智能水听器或地震检波器进行车载数据处理，以减少数据量，而数据量可以被触发以更高的频率进行短时间记录。我们将对新的智能传感器进行现场测试，从而展示它们如何回答重大科学问题。我们试图了解是什么触发了海底流动，以及这种初始触发机制如何影响流动行为。特别是，海底流动如何与危险的河流洪水、风暴或地震联系在一起，因此它们如何记录这些危险？不同环境中的潜艇流动是否表现出一致的行为模式，如果不是，是什么导致了这些差异？为了做到这一点，我们将在台湾近海的刚果峡谷(冲淡河流，被动边缘，没有气旋)部署这些新传感器。

Our overall aim is to make fundamental step-changes in understanding of seafloor processes and hazards by developing and demonstrating novel sensor systems, which can form widespread and long-term listening networks. These low-cost and energy-efficient sensors comprise hydrophones (acoustic noise in water column) and geophones (ground shaking). Data will be returned via pop-up floats and satellite links, as has been pioneered by the highly successful Argo Project for water-column profile.This type of low-cost network could have unusually widespread applications for warning against threats to valuable seabed infrastructure, monitoring leaks from CCS facilities or gas pipelines, or for tsunami warning systems. Here we aim to answer fundamental questions about how submarine mass-flows (turbidity currents and landslides) are triggered, and then behave. These hazardous and often powerful (2-20 m/s) submarine events form the largest sediment accumulations, deepest canyons, and longest channel systems on our planet. Turbidity currents can runout for hundreds to thousands of kilometres, to break seabed cable networks that carry >95% of global data traffic, including the internet and financial markets, or strategic oil and gas pipelines. These flows play a globally important role in organic carbon and nutrient transfer to the deep ocean, and geochemical cycles; whilst their deposits host valuable oil and gas reserves worldwide. Submarine mass flows are notoriously difficult to measure in action, and there are very few measurements compared to their subaerial cousins. This means there are fundamental gaps in basic understanding about how submarine mass flows are triggered, their frequency and runout, and how they behave. Recent monitoring has made advances using power-hungry (active source) sensors, such as acoustic Doppler current profilers (ADCPs). But active-source sensors have major disadvantages, and cannot be deployed globally. They can only measure for short periods, are located on moorings anchored inside these powerful flows (which often carry the expensive mooring and sensors away), and they need multiple periods of expensive research vessels to be both deployed and recovered. We will therefore design, build and test passive sensors that can be deployed over widespread areas at far lower cost. These novel sensors will record mass-flow timing and triggers; and changes in front speed (from transit times), and flow power (via strength of acoustic or vibration signal).We will first determine how submarine mass flows are best recorded by hydrophones and geophones, and how that record varies with flow speed and type, or distance to sensor. Our preliminary work at three sites already shows that hydrophone and geophones do record mass-flows. Here we will determine the best way to capture that mass-flow signal, and to distinguish it from other processes. This work will form the basis for designing a new generation of low-cost (< £5k) smart sensors that return data without expensive surface vessels; via pop-up floats and satellite links. Advances in technology make this project timely, as they allow on-board data processing by smart hydrophones or geophones to reduce data volumes, which can be triggered to record for short periods at much higher frequency. We will field-test the new smart sensors, and thus demonstrate how they can answer major science questions. We seek to understand what triggers submarine flows, and how this initial trigger mechanism affects flow behaviour. In particular, how are submarine flows linked to hazardous river floods, storms or earthquakes, and hence how do they record those hazards? Do submarine flows in diverse settings show consistent modes of behaviour, and if not, what causes those differences? To do this, we will deploy these new sensors along the Congo Canyon (dilute river, passive margin, no cyclones) offshore Taiwan.