National Geographic Today: Using Unmanned Subs to Probe the Deep

Bijal P. Trivedi
for National Geographic Today
August 16, 2001
Engineer Tom Austin removes REMUS—a five-foot (1.5-meter) missile-like object—from a rack at the stern of the Zodiac and places it in the water. As the propeller begins to spin, REMUS dips its nose beneath the surface and its sleek lime-yellow body melts into the teal waters off of Woods Hole, Massachusetts. It then glides back and forth across the ocean floor on a ten-minute preset test mission under a harbor of unsuspecting sailboats.

Oceanographers are developing a new generation of unmanned subs for probing deep ocean and coastal waters. These Autonomous Unmanned Vehicles (AUVs), of which REMUS is one, are expected to be the fastest and cheapest tools to comb the oceans, collecting precise chemical, geological, and physical data.

Oceans cover more than 70 percent of the Earth's surface, yet less than 5 percent of their underwater landscapes have been explored.

Although current AUVs are launched and retrieved by ships, oceanographers anticipate that fleets of these craft will eventually launch from underwater docking stations and will transmit their data via telemetry in real time. "With AUVs always ready to go, the craft could respond immediately to special events like an underwater eruption or earthquake on the seafloor," says Dana Yerger, an AUV researcher at the Woods Hole Oceanographic Institution.

"The real thing that we're trying to get out of this is data," says Roger Stokey, of the Woods Hole Oceanographic Institution, and a senior engineer on the REMUS project. "The goal isn't to create an AUV, it's just a means to an end."

The REMote environmental sensing UnitS (REMUS) are at the cutting edge of AUV technology and are fully autonomous. Once REMUS is given a location and told what to measure, off it goes. There is no communication with it after that.

The greatest advantage to these small, unmanned craft is that they can work in temperature extremes from the Arabian Sea to Antarctica, and in conditions and for periods that would be perilous for divers.

Keen Interest Shown by U.S. Navy

Once the U.S. Navy got wind of REMUS' capabilities it wanted to harness the technology to roam hostile coastlines searching for buried mines.

"During the Gulf War, they had no way of bringing troops ashore via ships because they didn't know where the minefields were," says Stokey. "They'd send in SEALs (special sea-air-land forces) under the cover of darkness to feel around for these mines. Nobody in their right mind would want that job."

REMUS with its sleek, light body is perfectly adapted for swimming in coastal waters and is expected to play an integral role in upcoming projects to map the ocean floor of coastal regions.

From Global Warming to Jellyfish Sensors

The AUVs are outfitted with an assortment of instruments that measure properties like temperature, the strength and direction of currents, the concentration of carbon dioxide gas dissolved in the water, and saltiness.

Such measurements provide data that are essential for building models that predict climate change, and improve daily weather forecasts. Discovering how much carbon dioxide is stored in the oceans, for example, is a critical factor in determining whether the oceans are a sink or source for continued emissions of this greenhouse gas.

Other plans are to load AUVs with sensors that detect a variety of environmental pollutants, or instruments that can sample and sort the microscopic life-forms lurking in the oceans' depths. Some researchers want sensors that will track jellyfish. Researchers anticipate that monitoring pollutants and water temperatures may help explain the loss of certain species of fish and aquatic plants, or the sudden appearances of toxic alga blooms. ABE (Autonomous Benthic Explorer) II—a model which looks something like a fusion of Noah's Ark and the Hindenberg—is a more portly AUV designed for deep ocean missions where it will map, photograph, and possibly collect samples from ocean vents spewing black plumes. "The original ABE can scale steep cliffs, but it does so somewhat inefficiently and uses a lot of power. ABE II will be able to go over much more difficult terrain more efficiently and make maps of much larger areas," says Yerger, who works on ABE II.

In the last six months AUVs have triggered huge commercial interest. Oil and gas companies want them to scout out oil reserves and optimum locations for sinking drilling platforms. They are also great tools for inspecting underwater tunnels and communications hardware.

Enhancing the Ocean Experience

There is one major disadvantage to using AUVs. "AUVs don't have smart people controlling them," says Yerger. They can only perform limited tasks, but they do so with a relentless precision that produces very high quality data. "If we program a vehicle like ABE to fly in a grid pattern over the sea floor, it does exactly what we've asked and it doesn't get tired, it doesn't get bored, so it produces very high quality data."

While AUVs are a welcome tool to scientists, keeping them from dangerous locations and releasing them from the tedium of making repetitive measurements, it is clear they will never replace a human presence in the ocean. But they can enhance it.

"I had a very exciting moment when we were out with ABE making maps of the seafloor in an area where the manned submarine ALVIN was scheduled to dive later that day," says Yerger. "Using the data from ABE we made very detailed maps that we were able to share with the ALVIN crew as they ate breakfast. They were thrilled, they were excited and they got a lot of work done that day."

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