20,000 colleagues under the sea

Rutgers Slocum Glider RU02 deployed in Sargass...

Fleets of robot submarines will change oceanography

SAILING the seven seas is old hat. The latest trick is to glide them. Sea gliders are small unmanned vessels which are now cruising the briny by the hundred. They use a minuscule amount of power, so they can stay out for months. And, being submarines, they are rarely troubled by the vicissitudes of weather at the surface. Their only known enemies are sharks (several have come back covered in tooth marks) and fishing nets.

Sea gliders are propelled by buoyancy engines. These are devices that pump oil in and out of an external bladder which, because it deflates when it is empty, means that the craft’s density changes as well. This causes the glider to ascend or sink accordingly, but because it has wings some of that vertical force is translated into horizontal movement. Such movement is slow (the top speed of most gliders is about half a knot), but the process is extremely efficient. That means gliders can be sent on long missions. In 2009, for example, a glider called Scarlet Knight, operated by Rutgers University, in New Jersey, crossed the Atlantic on a single battery charge, though it took seven months to do so.

Since that crossing, gliders have been deployed on many previously unthinkable missions. In 2010 teams from the American navy, the Scripps Institution of Oceanography and iRobot, a robot-maker based in Bedford, Massachusetts, used them to track the underwater effects of the Deepwater Horizon oil spill in the Gulf of Mexico. That same year a glider owned by Oregon State University watched an underwater volcano erupting in the Lau basin near Tonga. In 2011 a glider made by another firm, Teledyne Webb of East Falmouth, also in Massachusetts, tracked seaborne radiation leaked from the tsunami-damaged reactors in Fukushima, Japan. And the University of Newfoundland is planning to use gliders equipped with sonar to inspect icebergs, to work out whether they are a threat to underwater cables and other seabed infrastructure.

Skipping under the ocean

Ten years ago there were fewer than 30 gliders in the world, all built either by academic institutions or the armed forces. Now there are at least 400, and most are made by one of three firms: iRobot, whose product is called, simply, Seaglider; Teledyne Webb, which manufactures the Slocum Glider (named after Joshua Slocum, the first man to sail solo around the world); and Bluefin Robotics (the third member of the Massachusetts sea-glider cluster, based in Quincy), which sells the Spray Glider. Broadly speaking, these machines have three sorts of application: scientific, military and commercial.

At the moment, science rules the roost. For cash-strapped oceanographers, gliders are a blessing. Their running costs are negligible and, though buying one can cost as much as $150,000, that sum would purchase a mere three days of, say, a manned trip to the Southern Ocean.

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via The Economist
 

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