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Underwater glider recovery

Posted on 03.09.2009 - 12:00 EDT in AUV NEWS by Rons_ROV_Links

Underwater glider recoveryOn Monday 20 July 2009, an underwater 'glider' used by scientists from the National Oceanography Centre, Southampton (NOCS) to help understand the interaction between oceans and climate was successfully recovered by Spanish Search and Rescue off the Canaries after developing technical problems.

Underwater gliders are a new tool for oceanographers, providing data from below the sea surface, which cannot otherwise be easily be obtained. Gliders are able to profile temperature, salinity and currents in the upper kilometre of the ocean. While at sea, they surface several times a day and transmit the data they have collected via satellite communications, and the scientists are also able to send them new instructions.

Using an average of just 1.5 Watts, less power than most bicycle lamps, gliders have been designed for endurance. They are typically able to 'fly' from the surface to 1,000-metres depth and back to the surface, while travelling about 4 km horizontally, in around 3 hours. Gliders are propelled by changing their volume and hence their buoyancy. This is done by pumping oil from an inner reservoir into an expanding external bladder to make the glider rise, and letting the oil flow back into the reservoir at the surface to make the glider sink.

Data from NOCS's gliders are used in the RAPID-WATCH programme that monitors the meridional overturning circulation of the Atlantic. Also known as the 'Atlantic heat conveyor' this is the system of ocean currents that transports heat polewards, thereby influencing European climate.

One of the NOCS glider fleet, Dynamite, has been on deployment as part of the RAPID-WATCH project between the Canary Islands and Morocco since May. She recently left her station to return to Gran Canaria to be recovered and serviced before a second deployment. But during the weekend of 18/19 July, when about halfway home, she started to experience serious difficulties with her buoyancy engine. Unable to dive or navigate, Dynamite was left drifting helpless on the surface of the eastern Atlantic, some 50 nautical miles east of Gran Canaria in rough conditions.

RAPID-WATCH partner, Carlos Barrera Rodriguez, at the Canary Institute of Marine Science (Instituto Canario de Ciencias Marinas; ICCM) in Gran Canaria was contacted about organising a ship to recover the ailing glider. With waves up to 4-5 m, recovery by ICCM's ship was deemed too difficult and Carlos instead contacted the island's Search and Rescue (SAR) team.

Luckily, as the glider is fairly similar in size and mass to a human, the SAR team decided to recover it as training exercise! The team was first briefed about the glider and any possible associated hazards. Information from the glider's global positing system was transmitted via the Iridium network to NOCS and then ICCM and finally to the SAR spotter plane, which relayed the position to the SAR helicopter. A diver lowered into the sea and strapped the glider to a stretcher, which was then winched aboard the helicopter.

The whole operation went very smoothly and is a tribute to the professionalism of the SAR team in Gran Canaria. Paul Wright of RAPID-WATCH said: "For all of us who go to sea, we are constantly grateful that they are there to help save lives in case of serious emergencies, and this is a reminder about just how difficult it is to locate a small object in rough seas."

The National Oceanography Centre is pioneering the use of gliders, which, despite this recent hiccup, are becoming an important part of the monitoring network providing greater insight into an important component of the climate system. "Although there are sometimes setbacks such as this, the reliability of autonomous gliders has increased greatly and I expect to see them used much more widely in the near future," said RAPID-WATCH scientist Dr David Smeed.

The RAPID-WATCH programme is funded by the Natural Environment Research Council and will allow the observation in the Atlantic to continue until 2014.

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