The Potential of DAS on Underwater Fiber Optic Cables for Deep-Sea Current Monitoring

<p><span>Distributed Acoustic Sensing (DAS) </span>enables<span> the </span>use of <span>existing </span>underwater <span>telecommunication </span>cables <span>as multi-sensor arrays</span>, allowing for detailed<span> study of the seismic wavefield. </span>Since <span>underwater </span>telecommunication <span>cables </span>were not deployed for seismological investigations, <span>the coupling between the </span>cable and the seafloor varies<span>, dramatically reducing the usefulness of </span>poorly coupled<span> cable segments</span> for<span> seismological research. In particular, underwater cables include segments that are suspended </span>in the water column across seafloor valleys or other bathymetry irregularities. Here, we propose that <span>ocean bottom currents may be studied by monitor</span>ing the vibrations of suspended cable <span>segments</span>. We analyze <span>DAS-strain recordings</span> on <span>three dark fibers deployed in the Mediterranean </span>S<span>ea. </span>Several cable segments, presumably suspended, feature h<span>igh-amplitude signals with harmonic spectra</span> as expected from<span> a </span>theoretical <span>model of in-plane vibration of hanging cables. The spatial shape of the vibration modes are determined by filtering and stacking. Their comparison to theory allows constraining the attenuation of longitudinal waves propagating along the cable in the non-suspended sections. The vibration frequencies change over time scales of tens of minutes. </span>Assuming that<span> oscillations of </span>suspended<span> sections are driven by deep sea currents, the temporal fluctuations of the vibration frequencies</span> <span>are related to changes of the cable</span>s<span> tension which, in turn, are related to the drag force induced on the suspended cable by </span><span>the shedding of </span><span>Karman </span><span>vortex</span>.<span> On this basis, we propose a method to infer changes of deep sea current speeds from the changes of fundamental frequency of cable vibrations</span>. Submarine optical reconnaissance campaigns and controlled smaller-scale experiments are planned to validate the approach. <span>The work aims at </span>demonstrating the potential of using suspended telecommunication <span>cable</span>s<span> to </span>monitor and investigate <span>marine currents in </span>deep <span>ocean environments. </span></p>

Issues in Underwater Cables Deploymentby Risk Analysis

Underwater cable deployment facilitates the coverage and speed of internet all over the world for various applications like international trade, various communication transfers, and other daily end user requirements. Also, critical network infrastructure below the water remains largely unexplored to end users because they are not directly related with its development. However, the risk of damage or destruction by unintentional underwater accident or intentional malicious threats leads to costly and communications disruptions. This chapter solves two primary goals. The first is to highlight the issues in underwater cable deployment that may be seen or unseen leads to various potential risks that could interrupt cable-supported services. The second goal is to explore the various possibilities for securing the organization to ensure business continuity.

Utilizing the Ensemble Kalman Filter and Ensemble Kalman Smoother for Combined State and Parameter Estimation of a Three-Dimensional Towed Underwater Cable Model

A finite difference method (FDM) solving the coupled partial differential equations governing three-dimensional (3D) motions of a towed underwater cable has been implemented in a combined ensemble Kalman filter (EnKF) and ensemble Kalman smoother (EnKS), as a new approach to combined state and parameter estimation for towed underwater cables. A simulation study of the method applied to a seismic streamer has been performed. Cable state variables as well as model parameters are estimated. Parameters estimated are crossline ocean current varying with time as well as cable tangential drag coefficient. The presented results indicate that the method is able to estimate state as well as parameters for seismic streamers.

Review of Underwater Cable Shape Detection

Underwater cables play vital roles in marine engineering because they provide power and communication connections from the shore to an increasing number of sea installations. To ensure the system is operating reliably and continuously, it is necessary to detect the shapes of underwater cables in real time. However, this task is difficult to accomplish because the underwater cables are located in a dynamic and complicated subsea environment, which can cause changes in position, depth, and visibility.In this report, the current development of underwater cable shape detection methods, including visual, acoustic, magnetic detection, and multisensor fusion detection, and the advantages and disadvantages are described and analyzed. Furthermore, the disadvantages of these methods are addressed, which, based on survey platforms with high cost, include a long detection period and the failure to reveal emergencies. Then, the need to construct a simple and reliable system to detect the shapes of underwater cables is highlighted, and one possible solution based on bend sensors embedded in underwater cables is discussed.

THE SEAFLOOR MORPHOLOGHY OF SUNDA STRAIT FOR LAYING THE UNDERWATER CABLES

The coastal and offshore areas around the Sunda Strait will be developed to be a submarine cable corridor connecting between Java and Sumatra Islands. There are some requirements that should be considered before laying the underwater cables. One of these considerations is to understand the seafloor morphology of the Sunda Strait. The study was conducted based on six of track lines with 1 km line spacing and 4 Cross lines. The water depth obtained then was corrected to the depth of water from the Lowest Water Level (LWL). The seabed condition in the near shore area of Sumatra side is very flat and is influenced by 2 km offshore tide activity. The coast line is characterized by mangrove and fine fraction of sediments (mud and clay). At the Java side, the coastal morphology is characterized by the very steep slope and most of the area is occupied by the industrial activities. Keywords: seafloor morphology, under water cables, Sunda Strait Area pantai dan perairan Selat Sunda akan dikembangkan sebagai bagian dalam penempatan kabel bawah laut yang menghubungkan Pulau Jawa dan Pulau Sumatera. Rencana penempatan kabel bawah laut ini membutuhkan beberapa persyaratan teknis yang harus dipertimbangkan. Salah satu pertimbangan untuk peletakan kabel bawah laut adalah memahami morfologi dasar laut selat Sunda. Penelitian dilakukan berdasarkan 6 lintasan pemeruman dengan jarak antar lintasan 1 km, dan 4 lintasan memotong lintasan utama. Kedalaman laut yang diperoleh kemudian dikoreksi dengan muka laut terendah. Kondisi permukaan dasar laut di sisi pantai Sumatra sangat datar serta sejauh 2 km ke arah laut lepas masih dipengaruhi oleh aktifitas pasang surut. Garis pantainya dicirikan oleh tanaman bakau dan fraksi sedimen halus (lumpur dan lempung). Pada sisi Jawa, morfologi pantai dicirikan oleh kemiringan lereng yang curam dan kebanyakan area ditempati oleh aktivitas industri. Kata kunci: morfologi dasar laut, kabel bawah laut, Selat Sunda

The optical system in Borexino

Borexino detector is composed of 2214 photomultipliers (PMTs) collecting the scintillation light produced by the liquid scintillator. Phototubes are partially immersed in the scintillator and partially in high purity water. A proper electrical and mechanical selection of the devices as well as a custom-made encapsulation was mandatory for a long-term immersion in these two aggressive liquid. Underwater cables and connectors and optical fibers are also described in detail.