Spray AUV Makes History Crossing Gulf Stream

Launched about 100 miles south of Nantucket Island, the 2-metre orange glider looks like a model airplane with no visible moving parts. It slowly made its way toward Bermuda some 600 miles to the south of Cape Cod at about one-half knot, or 12 miles per day, measuring various properties of the ocean as it glided up to the surface and then back down to 1,000-metres depth (3,300 feet) three times a day. Scientists recovered the vehicle this week north of Bermuda.

Every seven hours Spray spends about 15 minutes on the surface to relay its position and information about ocean conditions, such as temperature, salinity and pressure, via satellite back to Woods Hole, Mass., and San Diego, Calif., where scientists Breck Owens from Woods Hole Oceanographic Institution, and Russ Davis and Jeff Sherman of Scripps Institution of Oceanography at the University of California, San Diego, track its progress.

It has been an adventure-filled voyage. After two false starts this summer, when malfunctioning equipment cut earlier missions short and the scientists had to recover the vehicle after a few days at sea, the 112-pound glider was launched (with fingers crossed) in September from the research vessel Cape Hatteras.

Like parents giving the car keys to a teenage driver for the first time, Owens, Davis and Sherman were apprehensive yet confident that the vehicle would reach Bermuda. The first week went smoothly, but when the vehicle began to cross the Gulf Stream, where surface currents can exceed six mph across the Stream's 30-mile to 60-mile width, Spray was taken for a fast ride back to the north. "We lost almost two weeks' progress in just two days," noted Sherman. The ability to communicate with the vehicle and send commands enabled the scientists to give it a new course each time it surfaced, and Spray eventually crossed the Gulf Stream and was back on track.

"It has been exciting, to say the least," Owens said. "We have just completed a track across the Gulf Stream and proved we can use gliders to monitor circulation patterns and major currents."

Spray has a range of 6,000 kilometers, or about 3,500 miles, which means it could potentially cross the Atlantic Ocean and other ocean basins.

"The key," said Davis, "is that Spray can stay at sea for months at relatively low cost, allowing us to observe large-scale changes under the ocean surface that might otherwise go unobserved."

Being able to communicate with the vehicle and change course or change the information it is collecting while at sea is a big step forward in the ability to gather information in the ocean.

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