Submarine fiber-optic cables offer high capacity, reliability, and excellent transmission quality, playing a vital role in both military and civilian communications, especially in international communications. However, these cables are often damaged by fishing nets, hooks, anchors, and other equipment, causing bending, deformation, or even breakage. Such damage leads to communication disruptions and significant economic losses. Repairing submarine fiber-optic cables is even more difficult than their initial installation. While shallow water areas can be inspected and repaired manually, locating a damaged cable less than 10 cm in diameter on the seabed, which could be hundreds or even thousands of meters deep, is like searching for a needle in a haystack. Currently, pinpointing and repairing breaks in submarine fiber-optic cables remains a major technical challenge.
Causes of Submarine Cable Damage
The factors contributing to submarine cable damage can be categorized into two main groups: human-induced factors and natural disasters. Human-induced factors include activities such as fishing operations, ship anchoring, and maritime construction projects. Natural disasters encompass events like earthquakes and tsunamis. Human activities are the primary cause of submarine cable damage. According to relevant statistics, approximately 95% of all submarine cable damage is attributed to factors such as marine aquaculture, fishing activities, ship anchoring (see Figure 1), and offshore engineering projects.
In recent years, with the deepening development of the oceans and the increasing frequency of offshore activities, human activities have posed an escalating threat to the safe operation of submarine cables, especially with the growing frequency of damage caused by ship anchors.
Typically, when an anchor is dropped, it can damage the insulation, conductors, and optical fibers of submarine cables, or even completely cut the cables, causing insulation failure, circuit damage, fiber optic failure, and in some cases, cable breakage.
Damage to cables caused by earthquakes is secondary, with the primary factors affecting submarine cables being collapses, landslides, and displacements.
Repair of Submarine Cables
First, the damaged submarine cable is tested to determine its condition and roughly locate the damage. Based on these results, a repair plan is created. Next, the cable is recovered. Following the salvage plan, a cable-laying vessel is used to retrieve the cable near the break, handle both ends of the break, and mark the location. Then, the seabed route in the repair area is cleaned, and a suitable route for repair and burial is chosen. After these steps, the submarine cable is reconnected. The salvaged cable is connected and insulated properly. Once the test shows normal results, the reconnection is complete. The repair section is then moved to the planned burial site and transferred to a burial machine for installation. A second reconnection test is conducted, followed by underwater robot testing of both ends of the break. Once the test passes, the cable ends are lifted, and the cable-laying vessel completes the installation, finishing the repair.
Throughout the repair process, accurately locating the break point is key. This involves testing the distance from the break to the shore and precisely pinpointing the exact location of the damage.
Submarine Cable Inspection Technology through ROV
Traditional methods involving divers and service vessels for cable inspection and recovery are being increasingly replaced by ROV. With their advantages in work depth, detection range, and continuous operation time, ROV have overcome challenges like depth limitations, diver working hours, environmental conditions, and the inefficiency of vessel towing. In deep-water areas, ROV have fully replaced divers and vessel-based operations for inspecting and maintaining submarine cables.
When ROV are used for submarine cable inspection, the process begins with using an AUV (Autonomous Underwater Vehicle) to scan the cable installation area and locate the cable break point (by sonar)
Next, an ROV (Remotely Operated Vehicle) is used to assist with the recovery. The ROV clears away the sediment to expose the submarine cable, cuts the cable with its manipulator, and then brings the cable to the surface. At the same time, the underwater robot places a wireless signal transceiver at the break point for use during future repairs. With the position provided by the transceiver, the other end of the cable is recovered to the surface. On the support vessel, the two cable ends are connected using the proper equipment, and a signal from the near-end landing station is tested to locate the faulty section of the cable. After cutting out the damaged part, the cable is reconnected, and a signal test is done. Once the communication is restored, the cable is re-laid underwater following the procedure.
The ROV’s working depth is not limited and can be customized according to the inspection requirements, allowing for different operating depths. This eliminates the risk to divers’ lives and significantly improves work efficiency.
MoxLab Solution
MHX II-C ROV is considered as the best platform, in which the M900 imaging sonar will be equipped to capture images of the cable connection points, and the TSS350, supported by a navigation positioning system, to inspect the cable routing and burial depth.
ROV
M900 Imaging Sonar Physical Image
TSS350 Subsea Cable Detection System
