The first scientific mission with Sentry, a newly developed robot capable of diving as deep as 5,000 meters (3.1 miles) into the ocean, has been successfully completed by scientists and engineers from the Woods Hole Oceanographic Institution (WHOI) and the University of Washington (UW).
The vehicle surveyed and helped pinpoint several proposed deep-water sites for seafloor instruments that will be deployed in the National Science Foundation (NSF)’s planned Ocean Observatories Initiative (OOI).
Sentry is a state-of-the-art, free-swimming underwater robot that can operate independently, without tethers or other connections to a research ship.
The autonomous underwater vehicle, or AUV, is pre-programmed with guidance for deep-water surveying, but it can also make its own decisions about navigation on the terrain of the seafloor.
“This investment into emerging technologies is paying off in delivering state-of-the-art science support,” said Julie Morris, director of NSF’s Division of Ocean Sciences. “In the near future, Sentry will conduct high-resolution oceanographic surveys that would be otherwise impossible.”
Working in tandem with sonar instruments on the UW-operated research vessel Thomas G. Thompson and with photo-mapping by WHOI’s TowCam seafloor imaging system, Sentry gathered the most precise maps to date of seafloor features known as Hydrate Ridge and Axial Volcano off the coast of Oregon and Washington.
The AUV can collect the data needed to make seafloor maps at a resolution of less than one meter. On this first cruise, Sentry collected as many as 60 million individual soundings of seafloor depth in a single dive.
Powered by more than 1,000 lithium-ion batteries-similar to those used in laptop computers, though adapted for extreme pressures, Sentry dove for as long as 18 hours and 58 kilometers, with the potential for longer trips in the future.
Sentry is designed to swim like a fish or fly like a helicopter through the water. The sleek hydrodynamic design allows the vehicle to descend quickly from the sea surface to the depths (about 3,500 meters per hour). The novel shape also gives the vehicle tremendous stability and balance while cruising through bottom currents.
The vehicle has thrusters built into its foils, or wings. Like an airplane, the foils allow the vehicle to gain lift or drag or directional momentum, as needed.
When necessary, the AUV also can hover over the bottom for close-up inspections, navigational decision-making, and for rising up and down over rugged seafloor terrain. The design allows the vehicle to start, stop, and change directions, whereas many AUVs tend to travel in one direction.
The AUV steers itself with a magnetic compass; long-baseline (LBL) navigation triangulated from underwater beacons; a sophisticated inertial guidance system (INS); and, when within 200 meters of the bottom, an acoustic sensor that can track the vehicles’ direction and speed with incredible precision.
“Sentry is a true robot, functioning on its own in the deep water,” said Rod Catanach, a WHOI engineer who works with Sentry. “The vehicle is completely on its own from the time it is unplugged on the deck and cut loose in the water.”
Eventually, vehicles like Sentry and its successors will plug into and interact with the ocean observatory system, using the power charging systems and high speed communications delivered by the submarine networks.
Further Reading: National Science Foundation
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