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Planet Earth

Run Silent, Run Deep

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Environmental scientists have only a sketchy picture of the oceans that cover the majority of Earth's surface. So they're excited about a new crop of autonomous vehicles that can cheaply venture into little-studied realms by drawing most of their power from the sea.

The Slocum Glider, designed by Webb Research Corporation in East Falmouth, Massachusetts, incorporates an experimental thermal engine driven by the temperature difference between warm surface water and cooler layers below. At depth, an onboard reservoir of hydrocarbon freezes and contracts, making the craft more buoyant. Up top, the glider fixes its position using a Global Positioning System locator and transmits its environmental report to a satellite. Then the hydrocarbon re-expands, sending the Slocum Glider on its next voyage—as far as 4,000 feet down. The University of Washington's new research vehicle, called Seaglider, takes a more active approach. It uses a battery-powered pump to shunt oil out of a bladder to increase buoyancy, causing the vehicle to rise when it reaches the bottom of its dive cycle. Seaglider also has wings that send it zigzagging to a maximum depth of 3,300 feet. "We can operate Seaglider for an entire year for $20,000, the cost of one day's time in a research vessel. That will let us measure temperature, salinity, dissolved oxygen, currents, and chlorophyll fluorescence much more cheaply," says oceanographer Charles Eriksen. A newer model, which should be ready in a couple of years, will voyage nearly 20,000 feet below, bringing most of the world's ocean volume within reach. 

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