Fleets of unmanned robots ply the Pacific Ocean.
Princeton University engineers aren’t swimming with the fishes but they are learning from them.
In research inspired by the graceful coordination of fish schools, a team of Princeton University engineers is participating in a month-long robotics experiment that involves launching fleets of unmanned underwater vehicles into the Pacific Ocean.
The researchers are testing the vehicles’ ability to move in formation through the water while mapping ocean currents and tracking marine microorganisms. The work, sponsored by the Office of Naval Research, could yield benefits for a wide range of fields from climate and ecological research to military surveillance.
The project, called the Autonomous Ocean Sampling Network, is taking place in California’s Monterey Bay and is the largest and most complex effort ever to test an entire fleet of autonomous underwater vehicles, while collecting real data about conditions under the sea. As many as 15 underwater gliders, each about six feet long and weighing more than 100 pounds, are making coordinated sweeps through Monterey Bay, with some heading more than 25 miles from shore and diving to depths of 3,000 feet.
The experiment is a multi-institutional collaboration involving a unique mix of biologists, ecologists, oceanographers and engineers.
The Monterey Bay Aquarium Research Institute is hosting and coordinating the experiment, which includes 10 other universities and research institutions. The Princeton team, led by Professor of Mechanical and Aerospace Engineering Naomi Leonard, is responsible for programming the gliders to move in formation while making their own decisions about where to go to collect the best possible data.
"The gliders are out there foraging for information, looking for rich data that helps us understand ocean processes," said Professor Leonard. The approach is inspired by the behavior of schools of fish, which could be seen as a coordinated network of sensors looking for the richest supplies of food, Professor Leonard said.
For many of the research groups, the experiment culminates years worth of individual efforts and tests their ability to mesh into a working system.
"It’s phenomenal," said Professor Leonard after launching and monitoring one of the first groups of vehicles. "I am so impressed by what these gliders can do. They just stay out there like workhorses and run autonomously."
The experiment is the first to attempt a system of immediate feedback in which the vehicles report data to oceanographers and biologists, who use the information to make on-the-spot refinements to computer programs that simulate conditions under the sea. Those scientists then predict how the ocean currents are likely to evolve and relay their predictions to the robotics and control experts, who adjust the routes and programmed behavior of the vehicles. The vehicles, in turn, track gradients of temperature, salinity or other features to find areas of interest and report back increasingly targeted data.
"There are so many dynamics in the ocean that we do not understand, and the dynamics of the vehicles themselves are not even certain," said Professor Leonard. "So the feedback is there to provide robustness; it’s a way to manage uncertainty."
This network of sensors represents a major step forward in researching the dynamics of the sea, said Jim Bellingham, director of engineering at the Monterey Bay Aquarium Research Institute and the leader of the project.
The best current techniques involve taking readings from stationary moorings or dragging instruments behind ships, but these often fail to zero in on the transitory shifts in currents and temperature that drive much of the ocean’s ecology. "We’re seldom in the right place at the right time," Dr. Bellingham said.
Professor Leonard said, "It’s amazing that we now have these sensors out there that are so smart and so capable, and they are providing an enormous amount of data."
The main phenomenon of interest in Monterey Bay is a plume of cold, nutrient-rich deep-sea water that rises toward the surface across the mouth of the bay. These upwelling events cause the plankton to "bloom," which supports the rich fisheries and other wildlife in the area.
The underwater vehicles are engineering innovations on their own. They are essentially gliders because they have no propellers, thrusters or any kind of external propulsion system. Instead, they are equipped with pumps that take in or eject water, which makes the gliders sink or rise. As they go down and up, the vehicles glide forward aided by fixed wings. They steer with a rudder or, in some cases, simply by shifting their batteries from one side to the other, which makes the glider bank.
This streamlined design requires a minimum of battery power and should allow the vehicles to remain at sea for weeks at a time. The gliders surface every few hours to relay data, accept new instructions and check their locations using the satellite global positioning system. While underwater, they coordinate their locations with the help of an onboard compass and a device that measures their altitude from the ocean floor.
The experiment began Aug. 3 and concludes Sept. 8.
Additional participating research groups include: the California Institute of Technology, California Polytechnic State University, Harvard University, the NASA Jet Propulsion Laboratory, the U.S. Naval Research Laboratory, the Naval Postgraduate School, the Scripps Institution of Oceanography, the University of California-Santa Barbara, the University of California-Santa Cruz and the Woods Hole Oceanographic Institution.