Rupert, the only condition involving live creatures affecting subsea lines that I am aware of was during the late Eighties. After the laying of TAT-8, ATT and its consortium partners were faced with repeated shark attacks on the new optical strand, not in deep water, as I recall, but at shallower depths near some islands. I suppose you could say that the sharks were attracted to a light fiber diet at that time.
Sharks were attracted to radiated energy from the cable. It could have been a "heartbeat signal," used in conjunction with keep-alive monitoring, or some form of resonating taking place caused by the power strand that runs throughout. I'm not certain about this, as you can plainly detect.
This was viewed as a totally-unexplainable situation for a time, and caused a lot of concerns over the future of subsea fiber systems. FUD abounded, and the Intelsat folks, not to mention the journos and pundits, were in their glory if I recall correctly.
The Labs folks had a man-made phenomenon on their hands, but someone figured out the sensory issues, and resolved the problem. I haven't heard anything on the subject since. Although, I never did get all of the details about the specific causes.
A cursory search just now was fruitless except for the following article concerning SAT-2 off of S.Africa. I suppose a full length description of what took place exists somewhere on the web, but this was prior to the advent of documents being pasted on the www real time, as they are now, hence, it would have to be something added in an historic context.
Note that in the account which follows, the survey team went to great lengths to avoid mountain ranges and crevices in the sea bed, and succeeded in laying the entire cable on the ocean floor.
From: telkom.co.za
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Did you know?
The optical-fibre cable lying between depths of 1,000 and 3,000 m has been
protected against sharks by an additional aluminium layer.
Scientists believe sharks may be attracted to the radiation field created by the
cable. The extra aluminium layer contains the radiation fields.
The cable deeper than 3,000 m is thought to be beyond the cruising limits of
sharks.
The cable at shallower depths is already armour-protected to prevent possible
damage from rocks, and much of it is buried to escape the snares of fishing
trawler nets.
The cable was laid at a speed of between 5 and 10 km/h by purpose-designed
cable-laying ships.
The 9,500 km cable was coiled by hand into large cylindrical tanks on the
vessels because there is no successful method of doing it mechanically.
The cable rests on the ocean bed at an average depth of 4 000 m. At the
deepest point, near St Helena, the cable took more than two hours to sink to
the bottom - 5,800 m below the surface.
The laying operation took some five months (started on 10 May 1992 at
Melkbosstrand and was completed on 11 October 1992).
Long before the cable was laid, the 15-company consortium spent almost R9
million on an ocean bed survey covering the entire route between
Melkbosstrand, Tenerife and Madeira.
By mapping the topography of the ocean bed with sonar, the purchasers were
able to select the safest route for the cable, avoiding steep mountain slopes
and deep trenches.
The SAT-2 cable carries a lethal voltage of 9 000 volts.
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And from the same site, a few words on cable fault repairs:
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What happends if a fault develops?
How does one locate a problem somewhere along a 9,500 km cable?
And when it is found, how is it repaired?
SAT-2 is fitted with a highly sophisticated, computerised remote control and surveillance system. It enables the condition or quality of the signal at each of the 82 submerged repeaters to be monitored.
By identifying the two repeaters closest to the fault, the maintenance crews are able to isolate a single 116 km length of cable. Low power DC testing from the terminals can further aid in locating the fault position.
Repairing the cable fault is an operation involving complex manoeuvering of the cable ship because the cable ends, when recovered to the surface, could be as far as 10 km apart. To accommodate this problem, an additional length of cable needs to be inserted. Such a repair operation could take up to a week during which time the cable ship needs to be kept stationary for 24 hours for each jointing operation. If a fault does occur, communications will be temporarily redirected via satellite or alternative cable systems.
I'm not sure if the "low voltage DC testing" mentioned is actually TDR related, as suggested upstream, or if those DC signals are used to control remote transponders within the repeaters, which in turn launch TDR probe signals. Or radiate soundings for sonar-like detection, even. But we're getting closer. BTW, the url above also covers fishing trawlers and net snags.
Regards, Frank Coluccio |
