From hunting and hiding submarines to planning SEAL missions, a fleet of 65 aquatic, submersible drones is already giving the U.S. Navy a tactical advantage.
Last fall Rutgers University ocean researcher Oscar Schofield headed a collaborative experiment called Gliderpalooza, which coordinated 15 aquatic, submersible research drones to sample the deep waters off the coastal Atlantic. About 5 feet long and shaped like tomahawk missiles, the gliders beam home their data every time they surface. The propellerless drones, jam-packed with scientific instruments, swim by changing their buoyancy—taking on and expelling a soda can's worth of water to sink and float. And they navigate under the waves by themselves. "The gliders are autonomous, so you just throw them in the water and off they go," Schofield says, though they can also take directions from operators when they surface.
With this robotic flotilla—part of the new wave of ocean-going drones—Schofield and his colleagues could gather a detailed picture of the ocean's temperature, currents, wildlife, and water quality at depths up to 650 feet. But even as ocean researchers use these gliders to track fish and help predict storms, the drones have attracted another admirer—the U.S. Navy.
"Right now the Navy is at the forefront of this technology," Schofield says, "and the Office of Naval Research really funded and developed these gliders in the first place." The Navy currently owns 65 of the same kind of gliders Schofield operates, with plans to expand to 150 by 2015. But the Navy's interest isn't exactly in science. The fleet of gliders is helping the Navy gain a tactical advantage in the ocean's future war zones.
"As the Navy plans for operations, they have to look into the future," says Frank Bub, the lead ocean modeler at the Naval Oceanographic Office. In other words: As the Navy maps out anything from a SEAL team silently breaching onto shore to a subsurface naval exercise, it must predict how the movement of the seas will affect its plans. "The Navy relies on ocean models not just to forecast future conditions but to fill in the gaps where data may never have been collected," Bub says.
This is where the gliders come in. By sending a scientific drone through or near an area of interest, the "gliders provide us real-time ocean data, and that has two major applications," Bub says. The Navy can use that data not only to check the accuracy of its models, but to adjust or correct them.
"If the Navy SEALs have a mission and they're going ashore, they definitely want to know what the ocean conditions are from when they leave their mother ship to when they land on the beach," Bub says. Gliders could provide temperature data so the SEALs wear the right gear, or gliders could give the most accurate description of currents so the SEALs swim in the right direction as quickly and quietly as possible.
Where the gliders can have the biggest impact are the places where the Navy can't or isn't allowed to go. While he's not at liberty to list them all, Bub points to places where the Navy currently has significant interest: "The Navy is in the western Pacific, the northern Indian Ocean, and the Navy spends time in the Mediterranean," he says. It's in these places (perhaps even around the increasingly tense East China Sea) that gliders could slip in silently to gather intelligence. "The gliders are clandestine," Bub says. "They spend very little time on the surface, they're not generally detectable, and although they communicate through the Iridium satellite system, they've been encrypted."
And Schofield says this type of clandestine mission could be done from far away. Even though the gliders swim at less than a mile per hour, their propellerless propulsion and battery packs allow them to stay at sea for up to a year. "And you can launch a glider pretty far away from a region of interest. I could deploy one a hundred miles away from where I have it fly in," Schofield says.
Hunting and Hiding Submarines
Much of the time submarines operate in the dark—they're often deployed to places with limited oceanographic data. Schofield uses temperature as an example. "Satellites observe sea surface temperature by using infrared light," he says, "but infrared light penetrates only centimeters into the water, so you can't really extract any information from very deep in the ocean." Without satellites, ocean modelers rely only on a few thousand global research buoys as well as ships and research stations, which combine to provide an uneven and low-resolution picture.
Bub says it's crucial for a sub commander to understand both the temperature and salinity of deep waters. That's because the key to avoiding detection is to understand not only how much sound you're producing but where and how far it's traveling, and temperature and salinity play important roles in how sound propagates underwater.
"Sound in warm water goes faster than sound in cold water, and just like light, it will refract and bend," with changes in the salinity, depth, and temperature of the water, Bub says. "So for submarine warfare, the key is to take these qualities and convert them into sound speed. Then we can run acoustic models and find out how the sound propagates through the ocean."
Here, too, undersea gliders—which take snapshots of the deep ocean several times per second—are ideally suited for the job. Although the current Navy drones can reach a depth of only 3000 feet, the Navy already has plans for a newer version that could dive to more than 1 mile below sea level. By mapping the deep seas, the Navy thinks it can find places that are best for hiding subs.
"And on the other hand, our destroyers and other antisubmarine warfare ships want to know where other submarines are," Bub says. By taking advantage of our glider-aided acoustic models, "we can actively put sound in the water," with things such as active sonar and sonobuoys, "which travels on paths that are determined by our ocean models," he says.