Sensors to Increase the Security of Underwater Communication Cables: A Review of Underwater Monitoring Sensors <s> Magnetometers/Gradiometers Sensors <s> Introduction - Why Submarine Cables? Douglas Burnett, Tara Davenport, Robert Beckman PART I: BACKGROUND Chapter 1 - The Development of Submarine Cables Stewart Ash Chapter 2 - The Submarine Cable Industry: How Does it Work? Mick Green PART II: INTERNATIONAL LAW ON SUBMARINE CABLES Chapter 3 - Overview of the International Legal Regime Governing Submarine Cables Douglas Burnett, Tara Davenport, Robert Beckman PART III: CABLE OPERATIONS - LAW AND PRACTICE Chapter 4 - The Planning and Surveying of Submarine Cable Routes Graham Evans, Monique Page Chapter 5 - The Manufacture and Laying of Submarine Cables Keith Ford-Ramsden, Tara Davenport Chapter 6 - Submarine Cable Repair and Maintenance Keith Ford-Ramsden, Douglas Burnett Chapter 7 - The Relationship between Submarine Cables and the Marine Environment Lionel Carter Chapter 8 - Out-of-Service Submarine Cables Douglas Burnett PART IV: PROTECTING CABLESHIPS AND SUBMARINE CABLES Chapter 9 - Protecting Cableships Engaged in Cable Operations Mick Green, Douglas Burnett Chapter 10 - Submarine Cables and Natural Hazards Lionel Carter Chapter 11 - Protecting Submarine Cables from Competing Uses Bob Wargo, Tara Davenport Chapter 12 - Protecting Submarine Cables from Intentional Damage: The Security Gap Robert Beckman PART V: SPECIAL PURPOSE SUBMARINE CABLES Chapter 13 - Power Cables Malcolm Eccles, Joska Ferencz, Douglas Burnett Chapter 14 - Marine Scientific Research Cables Lionel Carter, Alfred H.A. Soons Chapter 15 - Military Cables J. Ashley Roach Chapter 16 - Submarine Cables and Offshore Energy Wayne Nielsen, Tara Davenport) PART VI: APPENDICES AND KEYWORD INDEX Appendix 1 - Timeline of the Submarine Cable Industry Appendix 2 - Overview of the Major Submarine System Suppliers (1850 -2012) Appendix 3 - Excerpts of Most Relevant Treaty Provisions Keyword Index <s> BIB001 </s> Sensors to Increase the Security of Underwater Communication Cables: A Review of Underwater Monitoring Sensors <s> Magnetometers/Gradiometers Sensors <s> The changes of the seabed environment caused by a natural disaster or human activities dramatically affect the life span of the subsea buried cable. It is essential to track the cable route in order to inspect the condition of the buried cable and protect its surviving seabed environment. The magnetic sensor is instrumental in guiding the remotely-operated vehicle (ROV) to track and inspect the buried cable underseas. In this paper, a novel framework integrating the underwater cable localization method with the magnetic guidance and control algorithm is proposed, in order to enable the automatic cable tracking by a three-degrees-of-freedom (3-DOF) under-actuated autonomous underwater vehicle (AUV) without human beings in the loop. The work relies on the passive magnetic sensing method to localize the subsea cable by using two tri-axial magnetometers, and a new analytic formulation is presented to compute the heading deviation, horizontal offset and buried depth of the cable. With the magnetic localization, the cable tracking and inspection mission is elaborately constructed as a straight-line path following control problem in the horizontal plane. A dedicated magnetic line-of-sight (LOS) guidance is built based on the relative geometric relationship between the vehicle and the cable, and the feedback linearizing technique is adopted to design a simplified cable tracking controller considering the side-slip effects, such that the under-actuated vehicle is able to move towards the subsea cable and then inspect its buried environment, which further guides the environmental protection of the cable by setting prohibited fishing/anchoring zones and increasing the buried depth. Finally, numerical simulation results show the effectiveness of the proposed magnetic guidance and control algorithm on the envisioned subsea cable tracking and the potential protection of the seabed environment along the cable route. <s> BIB002
Typical objects that can be detected by magnetometers are pipelines, underwater communication and power transmission cables, anchors, chains, and UXOs. Detailed information about magnetometer operations can be found in  . In general, one ton (1000 Kg) of steel or iron is expected to give a 1 Newton anomaly at 30 m. The amount of distortion falls off as the cube with distance and is linear with mass, so it is possible to detect an object of 100 kg at 15 m or an object of 15 kg at 8 m, or an object of 2 kg at 4 m. These factors are for induced magnetic fields only. Many targets may have permanent magnetic effects or they can be hollow. This would imply changes in detection ranges. Gradiometers are pairs of magnetometers attached in tandem. The measurement differences between the two magnetometer sensors, divided by the distance separating them, gives the gradient of change of the magnetic flux lines. Magnetometers on AUVs are used to track underwater communication cables BIB002 . For the detection, low-frequency currents are applied to the cables' conductors producing coaxial alternating magnetic field that is measured by the magnetometers. Also, during the installation process of underwater communication cables it is necessary to perform a magnetometer survey in places where the survey route crosses existing cables or to detect ferrous metal objects that could lead to cable damages BIB001 . Focusing on the aim of this paper, magnetometers can be used to detect anchors or fishing trawls that, as mentioned in Section 2.3, constitute the main cable threats. Hence the importance of Magnetometers or Gradiometers in the construction of underwater cable surveillance networks. Table 19 presents the main specifications of identified commercial magnetometers/gradiometers. 