Shallow water isn't just cloudy; it's clogged with the detritus of humanity that sloshes against most of the world's shorelines. "The big challenge is finding mines in these high-clutter areas, filled with human trash -- cars, junk, old refrigerators," says Rob Simmons, a program manager at the Navy's Program Executive Office for Littoral and Mine Warfare in Washington, D.C. To help AUVs distinguish a mine from a hot water heater, the Navy is developing more powerful sonar that will provide higher-resolution acoustic images. Also under consideration for AUVs are magnetic gradiometers -- sensors that use internal magnets to detect changes in local magnetic fields caused by metallic objects -- and chemical sensors that would detect explosive materials leaching from poorly made mines.
Mines pose a hazard in deeper water as well. Typically this sort of mine floats near the water's surface, attached to cables moored on the ocean bottom. Here, detection is currently done not by dolphins and divers but by ships or helicopters towing submerged sonar sleds. Neither system, though, is ideal: The ships put themselves at risk by navigating mine-infested waters, and the choppers, flying slow over the water, make an easy target for enemy gunners. The Navy hopes AUVs could one day do the work instead. The area to be covered is vast, so this sort of AUV will be required to stay out for significant amounts of time.
The 28-foot-long Seahorse, specially built for blue-water mine sweeping, will come online this year. It can traverse 300 nautical miles on batteries that will keep it going for up to 72 hours. While the Seahorse, which operates 100 to 1,000 feet below the surface, is ready now, the Navy is working to develop another blue-water AUV by 2004. The Long-Term Mine Reconnaissance System, currently under development at Boeing, consists of two 20-foot-long, 21-inch-diameter vehicles that will be launched and recovered through torpedo tubes. LMRS uses a forward-looking sonar -- sending sound waves out like a movie projector -- to spot floating mines, and to steer clear of them and other obstacles while it patrols. Each LMRS vehicle will go out for several days at a time, mapping 50 square miles a day as far as 100 nautical miles from the sub.
Because they are "value added" devices, increasing the Navy's overall work force, AUVs will enable the military to be more proactive. In military parlance, AUVs would enhance "battlespace preparation." They could be sent out to map the ocean floor in areas of potential conflict -- identifying mines, dangerous currents and ideal landing routes ahead of time without alerting hostile countries that their shores are of interest. "We would hope to have the necessary mapping done before war breaks out," says Martha Head, an oceanographer at the Naval Oceanographic Office at the Stennis Space Center in Mississippi. Today that prep work is done by large oceanographic ships, which makes it expensive, manpower-intensive, and far from stealthy. Transferring the job to small, unmanned, expendable vehicles that could get close to hostile shores without attracting notice would increase efficiency by at least an order of magnitude, according to Swean.
TOMORROW: DETONATING MINES AND MORE
The purpose of mine seeking is to find access routes -- both for ships to enter harbors and for special operations forces to land on beaches. In addition to detecting where mines are, it's necessary to determine where they are not: Often the best strategy is to go around a threat rather than confront one. But when mines lie in strategic places, they must be removed, and usually the best way to do that is to blow them up.
Making an AUV that can spot objects that appear to be mines is one thing. That's where the Navy is now. Making an AUV that can determine whether an object is a mine and not a million-dollar piece of oceanographic equipment, then destroy it if necessary, is much more complicated. That's where the Navy ultimately wants to be.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.