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| Silent Green-Energy Glider |
 Since December of 2007, a bright yellow torpedo shaped robot has been criss-crossing the depths of the Virgin Islands.
Called the Slocum Thermal and developed by teams at the Wood's Hole Oceanographic Institute and the Webb Research Corporation, the robot is named after Joshua Slocum, the first man to single-handedly sail around the world. The device currently travels 40 miles between St. Croix and St. Thomas and reaches depths of over 13,000 feet. According to the Economist, the Slocum Thermal "could revolutionize the way oceans are studied."
More correctly called a sea glider and not a robot, the concept was developed in 1989 by Henry Stommel, whose vision was to create a portable observational system of autonomous devices.
Without an engine, these sea gilders move vertically as their buoyancy changes. The use of mechanical energy, created by "exploiting the difference in temperature between the warm surface of the sea and its cold depths", moves oil back and forth, causing the craft to either sink or rise depending on the direction of the oil being pumped. The craft's wings provide lift and a tail fin and rudder are used to steer.
Tracing a saw-tooth pattern through the water, the robot transmits data through its constant ascent and descent, using GPS to periodically adjust its positioning. Measurements taken include temperature, currents, acoustics, chlorophyll fluorescence and salinity calculations.
Dr. Dave Frantanoni of the Wood's Hole team told BBC News that the "gliders can be put to work on tasks that humans wouldn't want to do or cannot do because of time and cost concerns." In the past, sea gliders relied on underwater vehicles and research ships stationed to collect data, re-charge batteries and for support services. The Economist estimates the costs associated with such vehicles remaining at sea for extended periods of time exceeds "tens of thousands of dollars a day," as opposed to the very little monetary expenditure required for the Slocum Thermal.
One member of the Woods Hole team, the group working with the Webb Research Corporation, thinks the glider could operate for a year without having to be recovered. These long term studies of the ocean will contribute to the much needed understanding of the sea's reaction to climate change.
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