Spray AUV Makes History Crossing Gulf Stream

"We envision having fleets of gliders in operation in a few years," Owens said. "It could change the very nature of the kinds of questions we can ask about how the ocean works."

Spray glides up and down through the water on a pre-programmed course by pumping one liter (about four cups) of mineral oil between two bladders, one inside the aluminum hull and the other outside. By changing the volume of the glider, making it denser or lighter than the surrounding water, the vehicle floats up and sinks down while wings provide lift to drive the vehicle forward. Batteries power buoyancy change, onboard computers and other electronics.

The glider records its position at the beginning and the end of each dive by rolling on its side to expose a Global Positioning System (GPS) antenna embedded in the right wingtip. Researchers obtain data from the glider and send new instructions to it using a satellite phone system and an antenna embedded in the left wingtip.

Sensors on the glider can be changed for each mission. For the mission from Cape Cod to Bermuda, the Spray glider is equipped with a CTD (for conductivity, temperature and depth) instrument that measures temperature, salinity and pressure, and an optical sensor that measures turbidity in the water, which is related to biological productivity.

For the next mission in early 2005, the glider will make a round trip between Woods Hole, Mass., and Bermuda. For future missions it will also be equipped with an Acoustic Doppler Current Profiler (ADCP) to give vertical profiles of current speed and velocity. In the not-too-distant future, Owens and Davis expect that the gliders will be equipped with an entire suite of sensors that indicate the presence of dissolved oxygen, carbon dioxide, alkalinity and nutrients in the water.

The idea for developing a robotic glider like Spray that could travel in the ocean gathering data over long periods came 15 years ago from the late Henry Stommel, a scientist at Woods Hole Oceanographic Institution known for his contributions to understanding the dynamics of ocean currents, especially the Gulf Stream. Stommel honored the first man to sail around the world alone, Joshua Slocum, by naming his idea the Slocum Mission. Slocum departed Boston on April 24,1895, on his three-year circumnavigation in Spray, a sloop he rebuilt himself. The new underwater glider is called Spray to show its lineage from Stommel's idea and Slocum's brave voyage.

Sherman, Davis and Owens developed the Spray glider with support from the Office of Naval Research. Additional sensor development was funded by the National Oceanic and Atmospheric Administration's Climate Observations Program. The Gulf Stream project is funded by the National Science Foundation.

"Spray gliders can look at entire sections of ocean basins, like the North Atlantic, or serve as virtual moorings by keeping station at a single point," Owens said. "Unlike humans, who need to stop for breaks, gliders can carry out missions from several weeks to as long as six months. They are fairly inexpensive to build and easy to operate. We are looking forward to the day we can routinely send gliders out on missions from the comfort of our laboratories or even our homes ashore."

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