Underwater large-area high resolution monitoring by Distributed Optical Fibre Acoustic Sensors

环境科学中的许多问题涉及确定声波或地震信号的起源位置和时间。包括鲸鱼在内的各种海洋物种可以通过三角定位来追踪它们的声音。海底下的活动断裂和岩浆侵入可以通过跟踪相关的地震活动来定位。类似的方法也可以用于追踪海底逸出的气体，这在海底碳捕获和储存（CCS）的背景下非常重要，在这个背景下，重要的是要验证储存的气体不会逸出回海底。目前，在所有这些应用中，声音都是通过一个由相对较少数量（通常是几到几十个）点探测器组成的阵列来检测的，这些点探测器可以被拖曳或（更常见的）部署在海床上或附近。光纤分布式声学传感（DAS）是一项新技术，它允许沿着光纤在无限数量的位置进行声学测量，同时在测量密度和灵敏度之间进行权衡。这种纤维的制造成本也相对较低，按照目前的市场价格，涂有聚合物层的电信纤维每米的成本不到1便士。即使在纤维上加了额外的装甲以抵抗车辆的重量，它们的成本也只会增加到每米几英镑。因此，这项技术有可能以更高的精度定位和量化海洋内部和海底的声源，而且成本可能比目前可能的要低得多。由于对声波与位于水柱内或海底的DAS纤维之间的耦合理解不足，该技术在海洋中的应用受到了限制。在这项可行性研究中，我们建议使用南安普顿制造的DAS系统，该系统可以专门用于监测水声信号，并在商业系统中通常不使用的频率下工作，以重建海洋声场的3D地图。我们的方法是首先确定海洋中的声学信号与铺设在海底的DAS光纤产生的信号之间的关系。然后，我们将从海底光纤的传感中确定声源的3D模型。我们的下一步是确定如何适应和应用DAS技术，使其适用于海洋噪声源的探测、定位和量化。我们将在测试箱和海洋环境（南安普顿港内的一个码头）对新技术进行一些简单的测试。该项目将建立在目前由NERC、EPSRC、碳信托基金、皇家工程院和皇家学会资助的研究基础上，提供一种新型分布式声学传感器网络，能够对水声源进行高分辨率3D检测和分析

A variety of problems in environmental science involve determining the location and time of origin of acoustic or seismic signals. Various marine species including whales may be tracked by triangulating their vocalisations. Active faulting and magma intrusion beneath the seabed may be located by tracking the associated seismicity. Similar approaches may be used to track gas escaping through the seabed, which is now important in the context of sub-seabed carbon capture and storage (CCS), where it is important to verify that stored gas is not escaping back to the seabed. Currently in all of these applications, sound is detected by an array comprising a relatively small number (typically a few to a few tens) of point detectors, that may be towed or (more commonly) deployed on or near the seabed. Optical-fibre Distributed Acoustic Sensing (DAS) is a new technology that allows acoustic measurements to be made at an unlimited number of locations along a fibre, with a trade-off between measurement density and sensitivity. The fibre can also be manufactured relatively cheaply and at today's market prices telecom fibres coated with a polymer layer costs less than 1p per metre. Even with fibres are engineered with additional armouring to resist the weight of vehicles passing on them, their cost only increases to a few pounds per metre. Thus, this technology has the potential to locate and quantify sound sources in and beneath the ocean with much greater accuracy, and potentially much lower cost, than hitherto possible. Deployment of this technology in the ocean is limited by poor understanding of the coupling between acoustic waves and a DAS fibre within the water column or resting on the ocean floor. In this feasibility study, we propose to use a DAS system manufactured in Southampton, which can be specifically tailored for the monitoring of underwater acoustic signals and operate at frequencies commonly not used in commercial systems, to reconstruct a 3D map of acoustic fields in the ocean. Our approach will be to firstly determine the relationship between an acoustic signal in the ocean and the signal generated in the DAS fibre laid on the seabed. We will then determine a 3D model of the acoustic sources from the sensing enabled by the seabed fibre. Our next step is to then determine how to adapt and apply DAS technology so that it is suitable for detecting, locating and quantifying acoustic noise sources in the ocean. We will do some simple tests of the new technology in test tanks and in the marine environment (a dock within the port of Southampton). This project will build on research currently funded by NERC, EPSRC, Carbon Trust, the Royal Academy of Engineering and the Royal Society to provide a novel distributed acoustic sensor network capable of high-resolution 3D detection and analysis of underwater acoustic sources