- Underwater glider
An underwater glider is a type of
autonomous underwater vehicle(AUV) that uses small changes in its buoyancyin conjunction with wings to convert vertical motion to horizontal, and thereby propel itself forward with very low power consumption. While not as fast as conventional AUVs, gliders using buoyancy-based propulsion represent a significant increase in range and duration compared to vehicles propelled by electric motor-driven propellers, extending ocean sampling missions from hours to weeks or months, and to thousands of kilometers of range. Gliders follow a sawtooth path though the water, providing data on temporal and spatial scales unavailable to previous AUVs, and much more costly to sample using traditional shipboard techniques.
The concept of the glider was introduced to the oceanographic community by
Henry Stommelin 1989, when he proposed a glider concept called "Slocum" (after Joshua Slocum, the first solo circumnavigator of the globe by sailboat). He proposed harnessing energy from the thermal gradientbetween deep ocean water (2-4 °C) and surface water (near atmospheric temperature) to achieve globe-circling range, constrained only by battery power onboard for communications, sensors, and navigational computers.
By 2005, not only had a working thermal-powered glider ("Slocum Thermal") been demonstrated by Webb Research, but they and other institutions had introduced battery-powered gliders with impressive duration and efficiency, far exceeding that of traditional survey-class AUVs. The
University of Washington"Seaglider" and Scripps Institution of Oceanography"Spray" vehicles have performed feats such as crossing the Gulf Streamfrom the mainland USA to Bermuda, and, together with the Webb "Slocum", conducting sustained, multi-vehicle collaborative monitoring of oceanographic variables in Monterey Bay.
Originally conceived as testbed for the thermal-power gliders before developing into a platform of their own, the Webb Slocum electric gliders have been widely deployed since 2003. As one of its earliest users,
Rutgers Universityhas flown its fleet of gliders over 45,000 km (as of June 2008) in three of the five major oceans. In January 2007, Slocum glider RU06 became the first autonomous underwater vehicleto fly across the Antarctic Circleinto Antarctica, on its way completing a 22 day, 553 km mission along the western shelf of the Antarctic Peninsula.
Gliders typically make measurements such as
temperature, conductivity(to calculate salinity), currents, chlorophyll fluorescence, optical backscatter, bottom depth, and (occasionally) acoustic backscatter. They navigate with the help of periodic surface GPSfixes, pressure sensors, tilt sensors, and magnetic compasses. Vehicle pitch is controllable by movable internal ballast (usually battery packs), and steering is accomplished either with a rudder (as in "Slocum") or by moving internal ballast to control roll (as in "Spray" and "Seaglider"). Buoyancy is adjusted either by using a pistonto flood/evacuate a compartment with seawater ("Slocum") or by moving oil in/out of an external bladder ("Seaglider", "Spray", and "Slocum Thermal"). Commands and data are relayed between gliders and shore by satellite.
Gliders vary in the pressure they are able to withstand. The coastal "Slocum" model is rated for 200 meters depth. "Spray" can operate to 1500 meters, "Seaglider" to 1000 meters, and "Slocum Thermal" to 1200. In December 2006, a "Deep Glider" variant of the Seaglider achieved a repeated 3300-meter operating depth.
XRay Flying Wing
As of 2006, the US Navy
Office of Naval Researchis developing the world's largest glider, the Liberdade XRay, which uses a blended wing bodyhullform to achieve hydrodynamic efficiency. It is intended to quietly track diesel electricsubmarines in littoralwaters, remaining on station for up to 6 months, with major field testing beginning in August 2006 [ [http://www.onr.navy.mil/media/extra/fact_sheets/advanced_underwater_glider.pdf] ] .
Paravane (water kite)
* [http://www-pord.ucsd.edu/~rdavis/publications/MTS_Glider.pdf Underwater Gliders for Ocean Research]
* [http://news.bbc.co.uk/2/hi/technology/7234544.stm Robot glider harvests ocean heat]
* [http://spray.ucsd.edu/ "Spray" page at Scripps Institution of Oceanography]
* [http://www.apl.washington.edu/projects/seaglider/summary.html "Seaglider" page at Applied Physics Laboratory - University of Washington]
* [http://iop.apl.washington.edu/seaglider/ "Seaglider" Operations page at APL-UW]
* [http://marine.rutgers.edu/cool/auvs/ Rutgers University Coastal Ocean Observations Lab -- Glider Operations]
* [http://www.webbresearch.com/slocum.htm "Slocum" page at Webb Research Corp.]
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