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Linux-based AUV maps Antarctic sea ice thickness

Nov 25, 2014 — by Eric Brown — 1,149 views

Woods Hole Oceanographic used a Linux-based “SeaBED” AUV to build the first 3D map of Antarctic sea ice — and found it’s thicker than had been estimated.

Woods Hole Oceanographic Institute (WHOI), based in Massachusetts, announced the publication of a paper in Nature Geoscience on experiments run by an autonomous, Linux-based submarine called the SeaBED. The underwater survey indicated that Antarctic sea ice was thicker than had been previously estimated.

SeaBED heads for new dive site in Antarctica
(click image to enlarge)

With the SeaBED autonomous underwater vehicle (AUV), WHOI has created the world’s first detailed, high-resolution 3D maps of Antarctic sea ice. Multiple SeaBED AUVs conducted surveys in 2010 and 2012 of a half million square meters of ice in ten floes spread across Antarctica’s Weddell, Bellingshausen, and Wilkes Land sectors. WHOI was joined in the research by the Institute of Antarctic and Marine Science (Australia), Antarctic Climate and Ecosystem Cooperative Research Centre (Australia), and the British Antarctic Survey (UK).

The results show the Antarctic sea ice is thicker and more deformed than previously thought. Mean thicknesses range from 1.4 to 5.5 meters, with some floes measuring up to 16 meters, according to the paper, and 17 meters according to the WHOI press release.

SeaBED with chief inventor Hanumant Singh
(click image to enlarge)

Previous estimates, based on satellite imaging, visual shipboard estimates, and a few point measurements on thinner ice floes, had estimated the ice to be much thinner. While global warming is more dramatically thinning Arctic ice flows, the greater volume of ice locked up in Antarctic sea ice would have a greater potential impact on sea-level rise.

“Putting an AUV together to map the underside of sea ice is challenging from a software, navigation and acoustic communications standpoint,” stated Hanumant Singh, an engineering scientist at WHOI, whose lab designed, built, and operated the AUV. Hanumant Singh and Sandipa Singh spun off the research into a company called Seabed Technologies, which is selling a commercial version of the SeaBED 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,” continued Hanumant Singh, who is co-founder and CTO of the company. “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.”

SeaBED (left) and WHOI’s 3D map of Antarctic ice

The twin-hulled SeaBED is about two meters long and weighs almost 200 kilograms. It can cruise at up to one-half knot, and can dive to depths of 6,000 feet (2,000 meters). SeaBED typically “flies” at about 8 feet (2.5 meters) above the seafloor, snapping a photo every three seconds with the help of a strobe light, says WHOI. In this case, however, the AUV was traveling at only 20 to 30 meters deep and looking up. Seabed Technologies also sells special Puma and Jaguar versions rated for 5,000-meter depths that have 24 hour batteries instead of eight hours on the standard model.

Like the Bluefin Robotics Linux-based Bluefin-21 AUV, which was used in an unsuccessful search for missing Malaysia Airlines Flight 370 earlier this year, the SeaBED surveys the surface (or in this case the ice) in lines, like a lawnmower. The SeaBED was specially fitted with an upward-looking sonar device to measure ice thickness.

SeaBED runs Ubuntu Linux on a 1.2GHz Intel Pentium. Complete source-code is provided to users, “making sensor additions or vehicle maintenance much simpler than that of competing commercial offerings,” according to Singh’s SeaBED page on the WHOI website.

The electronics are located in the top hull, and the batteries and sensors are in the bottom hull. The two hulls are connected by “wet” cabling routed through the vertical struts, says WHOI. The upper hull holds most of the positive buoyancy while the lower hull houses the bulk of the negative buoyancy, thereby increasing stability in pitch and roll conditions.

Summary of SeaBED specs

Major SeaBED features, including Puma and Jaguar models, are listed below:

  • Processor — Intel Pentium @ 1.2GHz
  • Maximum depth — 2,000 m (standard); 5,000 m (Puma and Jaguar)
  • Navigation and communications:
    • RDI Workhorse Navigator ADCP for bottom-locked navigation (1200kHz DVL, iXSea Octans FOG, LBL/USBL)
    • RF radio modem with 2km minimum range
    • WHOI MicroModem for 10kHz Band-A acoustic communication and navigation
  • Sensor systems:
    • Imagenex Delta-T multibeam imaging sonar for bathymetry capture
    • SeaBird CTD sensor for measuring salinity and water temp. (pumped model 49 CTD Fastcat)
    • Navigation pressure transducer using Paroscientific depth sensor
  • Custom camera system:
    • Based on high dynamic range Prosilica cameras
    • 1-, 4-, and 11-megapixel cameras
    • 12-bit dynamic range
    • Gigabit Ethernet camera with associated strobe
  • Power — 2kWHr batteries at 8 hours (standard); 6kWHr Li Ion with 24 hours (Puma and Jaguar)
  • Operating system — Ubuntu Linux

Further information

More information on the SeaBED AUV may be found on the Seabed Technologies website, as well as the WHOI SeaBED page.

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