They call them “gliders,” but these move through water instead of air. Two new robotic gliders, which are autonomous underwater vehicles, powered by changes in their own buoyancy or by different temperature layers in the ocean, will be tested operationally off Southern California this winter. Both gliders were developed with support from the Office of Naval Research (USA), which is interested in such systems because they offer the Navy and Marine Corps potential tools for collecting data about regions of the ocean necessary for mine countermeasures and other tasks important to expeditionary warfare.

The Slocum Glider, developed by Webb Research (Massachusetts), uses a heat engine that draws energy from the ocean thermocline - a layer where the ocean’s temperature changes rapidly - the boundary between the warmer water above and the cooler waters below. The glider cycles thousands of times between the surface and a programmed depth, getting the energy it needs to change its buoyancy from the heat flow of the surrounding water. This long-range deep ocean glider is designed to cruise for five years in a vertical zig-zag from the surface to depths of about 5,000 feet and back. As it does so it measures salinity and temperature, plots currents and eddies, counts microscopic plants, and even records “biological” sounds like whale songs.

The second robot, developed by the University of Washington Applied Physics Laboratory, is called a Seaglider. It is propelled by buoyancy control and wing lift to alternately dive and climb along slanting glide paths. It dead reckons underwater between Global Positioning System (GPS) navigation fixes it obtains at the surface, and so glides through a sequence of programmed waypoints. It transmits data and receives commands via satellite data telemetry when it exposes an antenna above the sea surface for a few minutes between dive cycles. Seaglider has enough range to cross an entire ocean basin in missions that last months, all the while diving and rising between the surface and waters as deep as 3500 feet. It can be launched and recovered manually from a small boat with a crew of two, and so doesn’t rely on costly ships for its deployment. Seaglider collects high resolution pro-files of physical, chemical, and bio-optical properties of the ocean.