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AUV NEWS: New sub dives crushing depths

Posted on 27.02.2007 - 12:00 EST in AUV NEWS by Rons_ROV_Links

New sub dives crushing depthsScientists at the University of Washington have developed an autonomous underwater vehicle that can stay out to sea for up to a year and dive to depths of nearly 9,000 feet -- nearly three times deeper than the deepest-diving military submarines.

Known as Deepglider, the 71-inch long, 138-pound device is made of carbon fiber that can withstand the deep ocean's immense pressure. The energy-efficient, battery-powered glider carries sensors to measure oceanic conditions including salinity and temperature -- information that is key to understanding climate change. When the measurements are complete, Deepglider rises to the surface and transmits the data via satellite to onshore scientists. "Reaching a depth of 2,700 meters (nearly 9,000 feet) is quite a feat and promises to extend the nature and type of missions that can be carried out by gliders," says Princeton University engineering professor Naomi Leonard. "You could even imagine a heterogeneous fleet of gliders working in tandem at different depths to explore this otherwise impenetrable undersea."

  Deepglider prowls the test tank in Charlie Eriksen's lab. Photo: Courtesy Charlie Eriksen, University of Washington  

Deepglider opens up new research possibilities for oceanographers studying global climate change. The glider's first trip revealed unexpected warming of water near the ocean floor, and scientists are interested in studying whether the temperatures are related to global warming.

"The maiden voyage was wonderful," says Charlie Eriksen, professor of physical oceanography at the University of Washington in Seattle. "On every dive we got within 10 meters of the bottom and we were able to see some interesting bottom temperature and salinity variations that we didn't know about, that I certainly didn't expect."

During its maiden voyage, in November 2006, the glider remained at sea for 39 days and made 150 dives, the deepest of which was to 8,901 feet, just 33 feet shy of the sea floor.

To control Deepglider, Eriksen's team sends instructions by satellite. The battery-powered device's hydraulic pumps generate minute changes in volume that cause the vessel to rise toward the surface or plunge further into the ocean.

  Deepglider being lifted out of the ocean during a preliminary test run. Photo: Courtesy Charlie Eriksen, University of Washington  

When scientists want to collect the Deepglider, they send messages from a laptop telling it to stay on the surface. Using a GPS locator, scientists on a boat can motor directly to Deepglider's location and pull it aboard.

Gliders are a cost-effective alternative to traditional measuring techniques, which involve expensive boat-trips and floating instruments that simply drift with surface currents. Gliders allow scientists to take measurements over an extended period, and with the advent of Deepglider they can now observe oceanic conditions over longer timeframes at unprecedented depths.

One key to successful glider design is managing energy consumption. The device must be light and agile enough to consume little power. It also needs sufficient battery power to operate autonomously for months on end.

Traditional gliders consume about half a watt of energy moving at a rate of half a knot. Deepglider's power consumption is about half that because of its exceptionally stiff hull that's resistant to pressure. When pressure compresses a hull in a traditional glider, it gains buoyancy and requires more energy to control.

Boeing assembled the 4-foot hull on the same carbon-fiber machine used to mock up the fuselage barrels for the 787.

In addition to climate change research, Deepglider may help improve seismic monitoring. Devices already fixed to the seafloor could communicate with the glider. In an emergency, the glider could rise to the surface and transmit data onshore.

Russ Davis, a research oceanographer at the Scripps Institution of Oceanography, who works with the Spray underwater glider, is not so convinced by Deepglider. The upper ocean, he believes, holds more interest.

"If I were going to create another instrument, it would be a faster, shallower one with more sensors that looked at the upper ocean, where there are a myriad of exciting problems to be looked at," Davis says.

Eriksen agrees there is much of interest in the upper ocean, but adds, "there are certainly things worth looking for in the deep ocean, including the effects of climate change."

© 2007 Wired News

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