Collaborative Unmanned Vehicles Could Revolutionize Underwater Surveillance

A foreign submarine, lurking off the American coast, finds itself shadowed by a band of small metallic entities. When the sub turns to elude one tracker, another is waiting, almost as if they were cooperating. Soon the sub, acknowledging its vulnerability, breaks off and heads for mid-ocean.

This scenario couldn't happen yet, but research taking place at GTRI may make it possible within a few years. The project—called Homogeneous Collaborative Control of Unmanned Underwater Vehicles with Acoustic Communication—is aimed at developing robotic devices that could work cooperatively on a variety of subsurface missions.

Current unmanned air and ground surveillance vehicles are rarely autonomous. Instead, they're guided by human operators using joystick-type controls, explains GTRI senior research engineer Michael West.

By contrast, today's underwater surveillance vehicles have a small amount of autonomy built in—but only because water changes the behavior of radio-frequency (RF) communication, making joystick guidance difficult.

"Underwater vehicle autonomy today consists mostly of throwing a vehicle off the back of a boat, having it swim around, gather information and then return," West said. "Our program is aimed at using many vehicles that operate both autonomously and collaboratively—where, for example, one vehicle could say to another, 'I need your type of sensor, you need to come over here.' "

Such underwater technology could offer both military and scientific applications, he said. For instance, collaborative underwater vehicles might scrutinize a much larger area for enemy mines than current technology can, or might be able to perform highly complex anti-submarine warfare missions.

In oceanographic research, collaborative vehicles could study underwater movement and phenomena over a broader area and with more detail than current tools.

Unmanned underwater vehicle research is one of several projects in which GTRI is developing autonomous robotic devices. In the Micro Autonomous Systems and Technology (MAST), a multi-year initiative sponsored by the U.S. Army Research Laboratory, GTRI is working with a large number of universities and companies to develop small, intelligent mobile robots capable of collaboration as well as advanced locomotion.

West's research team has developed a prototype of the homogeneous collaborative unmanned underwater vehicle. Its shape is similar to a sonobuoy, a sonar device used for decades for submarine detection. Using the dimensions of a sonobuoy—4 7/8 inches by 36 inches—allows GTRI's new underwater vehicles to fit existing launchers on aircraft and surface vessels.

"Essentially, this is a sonobuoy that's both intelligent and mobile, that will triangulate a submarine's location much better than the static sonobuoys we have now," West said. "Imagine moving sonobuoys that can actually swarm together and communicate with one another."

Ultimately, underwater vehicles could communicate with unmanned air vehicles. In this way, airborne sensors could collaborate with underwater sensors to track a given target.

A number of challenges lie ahead for GTRI's underwater-vehicle team.

Developing a significant degree of autonomous operation is one hurdle. To address that requirement, the team is leveraging MissionLab, a multi-agent robotics mission specification and control software, developed at the Mobile Robot Laboratory at Georgia Tech under the direction of College of Computing Professor Ronald Arkin. The technology takes high-level military-style plans and executes them with teams of robotic vehicles.

Communications issues pose another challenge. The project is currently using acoustic communication to link its underwater units. Acoustic energy—the same sound energy used in sonar—is often employed for underwater communication because it travels well in water.

But acoustic communication has a number of drawbacks. For one thing, this technology transmits information at fairly slow data rates. Transmissions requiring high data rates, such as video, are not feasible. In addition, the transmission of acoustic information may be heard through the water channel, eliminating the stealth needed for many military missions.

Consequently, West and his team are also researching the use of radio frequencies for underwater communications.

The drawbacks of RF energy include a tendency for RF signals to weaken rapidly in water. But RF also has many advantages, including high data rates and high propagation speed. Finding the right techniques, West said, could allow RF to become the best communications technology for linking an underwater-vehicle swarm together.

RF provides an additional advantage—it crosses the water-to-air boundary, West added. That capability would allow underwater vehicles to collaborate with air vehicles without having to use surface buoys.

"Ultimately we are aiming for unmanned autonomous vehicles in all three mediums—air, ground, and water," West said. "They would then be capable of heterogeneous collaborative behaviors and become effective for a wide variety of missions."