Seagliders Break Endurance Records

By Roland Piquepaille

Ocean-diving gliders have a large autonomy, mainly because they don't have propellers. And they are used to gather oceanographic data such as temperature or salinity at a fraction of the cost of research vessels. Several Seagliders built at the University of Washington (UW) just broke endurance records. Two of these Seagliders, which are 1.8 m long and weigh 52 kg, were launched last September between California and Hawaii and reached the island of Kauai after 191 days in a trip of 1,860 miles. Both Seagliders did more than 500 dives down to 1,000 m during their trips. When a Seaglider reaches the surface, where it stays for only five minutes, it determines its position via GPS, uploads its data and downloads its new instructions via satellite. Meanwhile, two other Seagliders are still somewhere in the Labrador Sea for more than 193 days now and have yet to be retrieved. Read more...

Here are the facts about these Seagliders.

Two ocean-diving gliders built at the University of Washington were retrieved late last month near the Hawaiian island of Kauai after setting a world record by traveling a quarter of the way across the Pacific Ocean. Two other UW gliders, awaiting retrieval from the Labrador Sea, have set another world endurance record with a deployment of 193 days as of early April.

The Seagliders used in the Pacific Ocean were deployed in the water mid-way between California and Hawaii last September. They traveled the Pacific for 191 days, covering 1,860 miles. During that time one made 599 dives and the other 559.

	Seaglider's cylindrical hull is a series of arched anodized aluminum panels separated by ring frames. The hull is surrounded by a fiberglass fairing to give it a low drag shape. (Credits for image and legend: University of Washington)
	Seaglider can travel at slopes as gentle as 1:5 or as steep as 3:1. At gentle glide slopes the vehicle transits most efficiently, while steeper slopes are used to maintain position and act as a "virtual mooring." After each dive Seaglider dips its nose to raise its antenna out of the water. It determines its position via GPS, calls in via Iridium data telemetry satellite, uploads the oceanographic data it just collected, then downloads a file complete with any new instructions. (Credits for image and legend: University of Washington)

And here are more details about how the Seagliders work.

A Seaglider can dive from the surface down 3,300 feet and back up every 3 to 9 hours. It remains at the surface 5 minutes to transmit ocean data that it has collected, relay its position and receive instructions via the Iridium satellite phone network, before diving again. It travels at half a knot, driven not by a spinning propeller but by buoyancy control: a hydraulic system moves oil in and out of an external rubber bladder to force the glider up or down through the ocean. Moving its battery pack causes it to pitch its nose up or down or roll its wings to change compass heading.

And what are they used for?

The temperature, salinity and oxygen data gathered by the Seagliders will help the North Pacific Acoustics Laboratory scientists better understand acoustic propagation -- how sound is affected as it moves through the ocean. Acoustics can be used to probe such things as long-term ocean temperature changes and climate variability, and the role of internal waves in ocean mixing, says Bruce Howe, oceanographer with the UW's Applied Physics Laboratory.

Gliders also could be used to monitor changes in the world's oceans because of storms, such as hurricanes, and other natural events, such as El Niño. Sonar and other sensing devices mounted on gliders may one day routinely scan harbors and seaports for explosive mines or detect divers in areas where they don't belong.

For more information, you should visit the Seaglider home page. You'll find its specifications, an image gallery and animations (in QuickTime format).

Sources: University of Washington news release, April 5, 2005; and various websites

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