[ed. Drones above, gliders below. The remote-sensing/surveillance industry is booming these days.]
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. (...)
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.
Gliders, moreover, give a continuous view of what is going on, rather than the series of snapshots yielded by equipment lowered from a vessel at the surface. Besides tracking pollution, watching volcanoes and measuring icebergs, they are following fish around, monitoring changing temperatures in different layers of seawater and mapping the abundance of algae. The Ice Dragon, a modified Seaglider operated by the Virginia Institute of Marine Science, has explored under the Antarctic ice shelf, and another modified Seaglider, the Deepglider, can plumb the depths down to 6km (20,000 feet). Teledyne Webb’s Storm Glider, meanwhile, lurks in hurricane-prone areas, bobbing up to take readings during extreme weather.
Gliders are also quiet—so quiet that, as one researcher puts it, you can use them “to hear a fish fart”. This was demonstrated by a recent project run by the University of South Florida, in which a glider successfully mapped the locations of red grouper and toadfish populations on the West Florida Shelf from the noises the fish made.
by The Economist | Read more:
