Subsea Cable Location via Distributed Acoustic Sensing
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Solution Overview
Problem
Existing methods for locating and monitoring undersea cables are inefficient, as they rely on inaccurate plotted paths, drift due to ocean currents, and are prone to damage from shipping, earthquakes, and marine life, leading to costly repairs and service outages.
Innovation Solution
The method employs distributed acoustic sensing (DAS) using optical fibers deployed along the cables, where acoustic stimuli are transmitted from known locations to determine the cable's location through multilateration and monitoring for repeated disturbances indicative of potential damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If plotted paths from ship deployment are used to locate cables, then the cable location can be estimated, but the location accuracy deteriorates due to cable drift from ocean currents and deployment inaccuracies
Solution Approach 1:
The patent replaces the mechanical tracking system (ship position plotting) with an acoustic field-based detection system. Acoustic signals are transmitted through water and detected by sensors on the seabed to determine cable location, eliminating the accumulation of navigation errors and cable drift that plague mechanical tracking methods.
Solution Approach 2:
The patent introduces acoustic signals as an intermediary medium to transfer information about cable location. Instead of directly tracking the ship's position, acoustic waves are used to probe the cable's actual position on the seabed, providing accurate location data independent of deployment history.
2Measurement precision
If divers or submersibles are deployed to inspect cable deployment, then accurate cable path information can be obtained, but the complexity and cost of the inspection process increases
Solution Approach 1:
The patent enables the cable system to self-diagnose its location and condition. Acoustic signals transmitted through the water are detected by sensors that automatically determine cable position and identify potential issues, eliminating the need for manual inspection by divers or submersibles.
Solution Approach 2:
The patent replaces complex mechanical inspection systems (divers, submersibles, ROVs) with an acoustic field-based detection system. This substitution dramatically reduces operational complexity while maintaining or improving measurement accuracy.
3Measurement precision
If acoustic signals are transmitted from multiple locations to determine cable position, then location accuracy improves through multilateration, but the time and resources required for location determination increase
Solution Approach 1:
The patent employs periodic transmission of acoustic signals from multiple locations. By transmitting signals at regular intervals and using the time differences of arrival at the cable, the system achieves accurate multilateration positioning. The periodic nature allows for efficient data collection and processing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for accurate location and monitoring of subsea cables, reducing the risk of damage and repair costs by detecting potential issues before they become severe, thereby extending the cable's lifespan and minimizing service disruptions.
Implementation Method 1
Radiation which is backscattered from within the optical fibre is detected and analysed to reveal information about acoustic stimuli acting on the optical fibre
Implementation Method 2
acoustic stimuli are transmitted from known locations to determine the cable's location
Data Source
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Figure 3a~3b
Figure 4a~4b
AI summary
The present application described methods an apparatus for locating and/or monitoring subsea cables (101) having an optical fibre (105) deployed along its length. The optical fibre (105) is connected to a distributed acoustic sensing (DAS) interrogator unit to interrogate the optical fibre to provide a fibre optic DAS sensor. To locate the cable an acoustic stimulus is transmitted into the water from one or more known locations. The time of arrival of an acoustic signal matching the stimulus at the sensing portions of the DAS fibre can be detected and used to determine information about the location of those sensing portions to the known location. The DAS signals returns can also be monitored under ambient conditions to detect any signals indicative of likely damage to the cable.