November 25, 2014
Robot Surveys Antarctic Sea Ice From Underneath
April Flowers for redOrbit.com - Your Universe Online
Scientists from the Institute of Antarctic and Marine Science (Australia), Antarctic Climate and Ecosystem Cooperative Research Centre (Australia), Woods Hole Oceanographic Institution (USA) and British Antarctic Survey (UK) have created the first detailed, high-resolution 3-D maps of Antarctic sea ice. This historic feat of cartography was made possible by a new underwater robot, which the team says provides accurate ice thickness measurements from areas that were previously too difficult to access.A wide range of technologies and techniques are used to measure sea ice thickness - from satellite observations for measuring large-scale thickness, to drilling cores from the ice and observations made from ships. Although the satellite images can be difficult to interpret because of snow cover, all three methods are critical for building a complete picture. They still leave gaps in our knowledge, however. The new Autonomous Underwater Vehicle (AUV) named SeaBED is proving to be an invaluable tool for filling those gaps.
The AUV was fitted with an upward-facing sonar, contrary to typical setups, in order to measure and map the underside of the sea ice floes. Operating at a depth of 60 to 90 feet, SeaBED was driven in a lawnmower pattern which merged lines of data to form high-resolution 3D bathymetric surveys of the underside of the ice.
SeaBED is approximately six feet long, 440 pounds and yellow, with a twin-hull design that provides enhanced stability for low-speed photographic surveys.
"Putting an AUV together to map the underside of sea ice is challenging from a software, navigation and acoustic communications standpoint," said Hanumant Singh, an engineering scientist at the Woods Hole Oceanographic Institution (WHOI) whose lab designed, built and operated the AUV.
"SeaBED's maneuverability and stability made it ideal for this application where we were doing detailed floe-scale mapping and deploying, as well as recovering in close-packed ice conditions. It would have been tough to do many of the missions we did, especially under the conditions we encountered, with some of the larger vehicles."
According to Jonathan Amos of BBC News, what the researchers found was unexpected — a greater thickness to the ice pack than previously estimated. They caution, however, against making generalizations from such a limited sampling.
The vast majority of Antarctica's floating sea ice is underwater, much like an iceberg. This means it is hidden from satellites and difficult for ships or core drilling to take direct measurements from.
"If we don't know how much ice is there is, we can't validate the models we use to understand the global climate," Ted Maksym, an oceanographer at the Woods Hole Oceanographic Institution, told Becky Oskin of LiveScience. "It looks like there are significant areas of thick ice that are probably not accounted for."
According to Dr. Jeremy Wilkinson from British Antarctic Survey (BAS): "The AUV missions have given us a real insight into the nature of Antarctic sea ice - like looking through a microscope. We can now measure ice in far greater detail and were excited to measure ice up to 17 meters thick."
The research team plans to continue their studies with large-scale surveys that can be compared to large-scale aircraft and satellite observations.
"What this effort does is show that observations from AUVs under the ice are possible and there is a very rich data set that you can get from them," Maksym added. "This work is an important step toward making the kinds of routine measurements we need in order to really monitor and understand what's happening with the ice and the large scale changes that are occurring."
The results of the study have been described in a recent issue of Nature Geoscience.