* 14:55 08 February 2008
* NewScientist.com news service
* New Scientist staff and Reuters
The new glider harnesses the temperature difference felt at different depths
A seagoing glider that harvests heat energy from the ocean to propel itself is being used to explore the undersea environment off Puerto Rico, say US researchers.
They said the glider had crisscrossed the 4000-meter-deep Virgin Islands Basin between Saint Thomas Island and Saint Croix Island east of Puerto Rico more than 20 times since it was launched in December 2007. See a video of the glider in action (28 MB, .avi).
And it could keep going on its own for another 6 months, the team at the Woods Hole Oceanographic Institution and Webb Research Corporation in Massachusetts, US, predicts.
Instead of using motors and propellers, underwater gliders propel themselves by altering their buoyancy. Still, most gliders use internal motors to adjust their centre of mass by pumping water or oil between the craft's pressurised inner hull and its outer one.
Hot wax
The new glider instead harnessed the temperature difference at different depths. Warmer surface waters heat wax-filled tubes, expanding the wax, and creating mechanical power driving internal pumps. Cooler water at lower depths reverses the process.
In future, such robots could autonomously monitor ocean conditions, carrying sensors that measure temperature, salinity and biological activity. They would only need to surface occasionally to fix their position using the Global Positioning System and to communicate via satellite to a laboratory.
"Gliders can be put to work on tasks that humans wouldn't want to do or cannot do because of time and cost concerns," says Dave Fratantoni of Woods Hole. "We are tapping a virtually unlimited energy source for propulsion."
Fratantoni adds that data collected by the gliders could help researchers understand how eddies in the region affect ocean circulation and disperse the larvae of fish, as well as pollutants. "They can work around the clock in all weather conditions," he says.
