Last month, a new kind of aquatic robot took a test cruise through the waters of Monterey Bay off California. The Tethys autonomous underwater vehicle (AUV), developed by the Monterey Bay Aquarium Research Institute (MBARI), could be just the thing to circumvent some of the problems that have been holding back marine research bots:
The two types of AUVs that researchers have relied on in the past both had their drawbacks. Propeller-driven vehicles could travel at a relatively quick pace and carry big payloads but could only be out at sea for a few days. Another type, called gliders, could endure weeks-long expeditions but were seriously lacking in the speed category. Traditional gliders top out at about 0.5 mph, according to the team’s statement. [CNET]
Tethys, however, enjoys the best of both worlds—endurance and scientific prowess. It employs variable buoyancy, rather than the less efficient “slightly buoyant” feature most AUVs use so they’ll float up to the surface in an emergency. Its power-saving software turns off systems not in use. All this, plus its efficient propeller and hull design, allows Tethys to save enough energy to carry sophisticated scientific equipment and still stay out to sea for more than a few days.
UPDATE: Jim Bellingham, the creator of Tethys, responded to DISCOVER with more details about what allows Tethys to be so efficient:
“The challenge is that at low speeds (say 0.5 meters per second) the vehicle control surfaces (e.g. the wing-like systems on the back of the vehicle) don’t work as well. This is because the force created by the surfaces is proportional to the square of the speed. So when the vehicle goes half as fast, the control surfaces generate a quarter the force. As the speed drops, in order to generate the same force, one operates at a higher and higher angle of attack (this is the angle between the body and the flow). The problem is that these high angles of attack also have much higher drag. We get around this problem by giving the vehicle the ability to change its buoyancy and the shift weight internally, so we don’t need to generate high forces on control surfaces. Bottom line: for most vehicles as they go to low speeds, they become less efficient, but not Tethys.”
Bellingham says he spent four years trying to build this machine.
In the past, studying phenomena like algal blooms depended on luck and timing — oceanographers would stick an instrument on a mooring and hope algae would drift past it, or they would schedule a cruise and hope the bloom would happen while they were at sea, he explains in a MBARI news story. “Tethys can travel to a spot in the ocean and ‘park’ there until something interesting happens,” he said. Once a bloom occurs, Tethys can switch into high gear and follow the bloom as it evolves, much like biologists on land would follow migrating animals. [Popular Science]
That ability to chase algae wherever they might go is what drove Bellingham to create a bot like Tethys, he tells DISCOVER:
“Imagine you were studying American teenagers, and you got to take a ‘teenager sample’ once a week. If you only observe them occasionally – say in the mall, which might be a good place to observe teenagers – you miss all these other factors which are important. In the ocean we are in the same situation – we observe the organisms briefly, and attempt to relate the state of the organisms to the environment in which we observe them. But just like our teenage example, to really understand these organisms, we need to know the ‘life experiences’ that shaped them.
Not only are marine micro-organisms the bottom of the food web in the large ecosystem on the planet, but marine micro-organisms play key but poorly understood roles in biogeochemical cycles such as the carbon and nitrogen systems. Half of the oxygen we breath is cycled through marine phytoplankton. Major changes in microbial ecosystems could have dramatic consequences for humans. Since we know we are changing the marine environment though ocean acidification and changing temperatures, an ability to predict how marine organisms might respond is essential.”
The study of marine life isn’t the only ocean science that may benefit from a bot like Tethys. Long-range explorers could also take unprecedented measurements of the water itself, and the way it moves far away from land.
Francisco Chavez, a senior scientist at MBARI, says he’s excited by the thought of using the robot for other projects. One of his ideas is to study how whirlpool-like eddies hundreds of kilometres from shore affect the ocean environment. Because of the time taken to travel to them by ship, by the time a typical 20–30-day expedition reaches an eddy they have just five days or so to study it before they need to return to shore. The Tethys “will allow us to follow these eddies for essentially an unlimited time,” Chavez says. [Nature]
To see other marine robots pushing the boundaries of exploration, check out the DISCOVER photo gallery. And for more on robot autonomy—and the ethical implications of war machines thinking for themselves, check out the feature “How Does a Terminator Know When Not to Terminate?”
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Images: Todd Walsh/MBARI