Robots could be used to sniff out oil spills and algal blooms in the ice-covered Arctic. One of these so-called long-range autonomous underwater vehicles has now traveled under the ice.
In a recent field trial, a long-range autonomous underwater vehicle (LRAUV) known as Polaris traveled beneath an ice sheet in the Arctic. It was launched by the Monterey Bay Aquarium Research Institute (MBARI) and Woods Hole Oceanographic Institute (WHOI).
Autonomous underwater vehicles (AUVs) can carry a variety of instruments, including those that measure water temperature, collect water samples, or record sound underwater. Scientists and engineers generally deploy these robots off the side of a ship. The vehicle then navigates the surrounding waters on its own, and completes its mission within a day or two, according to a statement.
Polaris is one of MBARI’s LRAUVs designed to stay out in the water for weeks at a time. It is much more cost-effective than using a research vessel and crew to collect the same data, writes the statement.
“Long-range capabilities for AUVs are still relatively new,” said MBARI Senior Software Engineer Brian Kieft in the statement. “All our LRAUVs were designed to eventually be able to operate with an overhead ceiling—such as an ice sheet—but this project is unique because, after almost 25,000 hours at sea, it’s the very first time an LRAUV has actually been under the ice.”
Most AUVs come to the surface periodically, using GPS to figure out where they are. But surfacing is not an option when operating below an ice sheet; instead, Polaris maneuvers through the water using its speed, heading, proximity to an acoustic beacon, and sonar to estimate its position continually.
While Polaris travels under the ice, scientists can keep tabs on the robot and download small amounts of data using an underwater acoustic transducer lowered into a hole in the ice.
The LRAUV can detect and locate such acoustic beacons up to five kilometers (over three miles) away. Researchers can expand the LRAUVs range by drilling additional holes in the ice and placing transducers in them. “That gives you five kilometers of range around each hole where you can still get data back and determine what’s happening,” explained Kieft.
At the end of its mission, Polaris needs to find and dock to a rope hanging through the ice—its docking station. The under-ice LRAUV is equipped with a special docking nose framed by two metal “whiskers” that help it latch onto this thin vertical line. By homing in on an acoustic beacon, the robot can return to the dock if there are any issues during deployment. “That’s home sweet home,” said Senior Mechanical Engineer Brett Hobson. “The dock is the only place where it can stop, the only place where it is safe.”
Photo credit: Ben Yair Raanan, 2020 MBARI