Hi-tech Kon-Tiki of research
Underwater glider tests ocean currents via remote control
SAN DIEGO — Scientists have probed the oceans for decades by towing instruments from the back of research ships or by tossing them overboard and picking them up weeks or months later.
But a new "smart" device promises remote-control measurement of the world's oceans: a self-propelled glider that sails across the ocean using underwater currents and its own changing buoyancy for propulsion.
In fact, its creators eventually hope to send it from San Diego to Hawaii all by itself.
The Spray, a six-foot-long device resembling a cruise missile, is designed for long-distance, long-term reconnaissance of underwater conditions: temperature, depth, salinity, and chemical signatures that give scientists clues about the makeup of the marine world.
The Spray is one of a new class of ocean instruments known as autonomous underwater vehicles. These AUVs follow a prescribed pattern in the sea and then return to a set pickup point. They are particularly useful in measuring the properties of ocean currents, coastal areas, or ocean dump sites. They operate for several hours on battery power, then report their position to ship or shore through the satellite relays and the global positioning system (GPS).
What's different is that the Spray doesn't have a motor and so it isn't forced to return when its batteries run down.
"It can navigate like a commercial airliner," says Jim Dufour, an ocean engineer at the Scripps Institution of Oceanography in La Jolla, Calif., who developed the Spray along with colleagues at the Woods Hole Institution of Oceanography in Woods Hole, Mass. "It knows where it is, where it's going to go, and it keeps track of all of its motion."
The Spray moves through the water like a true glider. By rolling a set of weights forward, the nose of the Spray begins to sink. Two-foot wings and a rudder direct it forward through the water. It also uses a gyroscope and accelerometer much like an airplane's and makes simple turns by shifting weights from side to side.
When it reaches a certain depth (a maximum of 1,000 meters or 3,280 feet), a canister of oil is squeezed into a rubber bladder outside the main compartment. This changes the volume but not the mass of the entire device.
"We're using Archimedes' principle," Mr. Dufour explains. "If we increase the volume, the density changes." As the craft becomes less dense than the surrounding water, it rises. The aerodynamically shaped wings provide additional lift, just like an airplane.
Using this relatively simple method of rising and falling, the Spray can sail for months at a time. After it returns to the sea surface, it rolls over on its side, and using a built-in antenna on its wing, gets a GPS fix and sends information back home.
Scripps researchers completed final testing of the Spray last month in the deep underwater canyons of Monterey Bay, Calif., where it stayed out for seven days at a time.
Funded by the US Navy, the $25,000 device will be deployed next year to measure the California Current, which flows southward from the Oregon-California border to Mexico. Scientists want to study this ocean river to help predict the success of several commercial fisheries.
The Spray took two years to develop. It is named for the 37-foot wooden sailboat that Joshua Slocum single-handedly sailed around the world from 1895 to 1898. If all goes well, Dufour and Russ Davis, a physical oceanographer at Scripps, and Breck Owens, a Woods Hole oceanographer, have similar transoceanic plans for the new Spray.
They plan to sail it from San Diego to Hawaii within two years. Another proposal is to send it from Woods Hole to Bermuda to study the Gulf Stream current.
(c) Copyright 1999. The Christian Science Publishing Society