My friend Chris Murphy is a graduate student in the MIT/Woods Hole Oceanographic Institute joint program. Late last summer his group went on a research cruise to the Arctic Circle, so I asked him to tell me a little bit about the two underwater vehicles they used for their work. Read on for the interview and some of his pictures from the cruise!
Explain a little bit about your graduate program and how the MIT/WHOI relationship works.
I'm an Engineering student in the MIT/WHOI Joint Program in Oceanography, working towards a PhD. That means that I take classes and perform research at both MIT and Woods Hole Oceanographic Institution. At MIT, I'm in the Computer Science and Artificial Intelligence Lab (CSAIL). At WHOI, where my advisor is located, I'm in the Deep Submergence Laboratory (DSL), studying underwater robotics. My research in particular is on the intersection of computer vision and acoustic communication strategies.
Can you tell us more about the DSL's research?
My advisor, Dr. Hanumant Singh, has focused on AUVs for imaging applications, such as generating 3D photo mosaics of the seafloor. Our group has three autonomous underwater vehicles, or AUVs, custom-built for that purpose: SeaBed, Puma, and Jaguar.
Tell us about the expedition's goals. What were you looking for?
This past summer we deployed and recovered AUV's from the middle of the Arctic ice pack. We deployed and recovered the vehicles several times, employing a variety of novel techniques for recovering the robots through the ice. We were trying to characterize the seafloor around hydrothermal vents in the Arctic -- both biologically and geologically. We were lucky to be on the Swedish icebreaker Oden, which had a fantastic crew, and really facilitated a lot of the work.
Why use robots to do what you needed to do?
As most of the area we worked in was covered with a few meters of ice, sending humans down in a manned submersible would be an extremely dangerous proposition, requiring perfect planning and execution. Even with the AUVs, the 'hole' in the ice that we were driving to was approximately 100m on a side, or about a shiplength. That's not much room for error. Using AUVs allowed us to run longer missions, and run missions in conditions that would have prevented diving with a manned submersible. Losing an AUV was a very real possibility, but one that is infinitely more acceptable than losing a manned submersible. AUVs are also capable of free-swimming; they could perform large-area or small-area missions as the scientists required, and weren't limited by places the ship could drive as a tethered vehicle might be.
What was the most challenging part of the AUV design?
The high pressures present at 6000m (the depth at which these AUVs were operating) dominate much of the design, which combined with the need for watertight enclosures makes for large metal enclosures around everything. It also takes a very long time to dive 4km, which means that it requires a lot of power, and therefore lots of batteries. That makes the vehicle even larger. Cold turns out not to a be a huge problem, as ocean temperatures at depth are already quite low regardless of location. Operationally, the cold and ice pose much larger challenges, ranging from difficulty working with connectors to the dangers of ice severing cables hanging from the ship.
What was new about Puma and Jaguar compared with similar vehicles?
The design for Puma and Jaguar is based off of the design of SeaBed, a robot designed over the last several years by the lab. Jaguar and Puma are rated to dive much deeper than SeaBed (6000m versus 2000m), and each has a different sensor payload. In addition, we made a variety of changes to our proprietary control software that made the vehicles more appropriate for Arctic operations. One such change was to the way that the AUVs handle abort conditions and return at the end of a mission. In traditional open-water operations, the AUVs can simply surface at the end of the mission, and the ship can be driven to their location. In Arctic operations, it is extremely likely that the AUVs would surface under the icepack, a situation we very much wanted to avoid. For Arctic operations, the AUVs each had a pre-programmed 'home' location about 100m deep that they would drive to at the end of the mission or if things went wrong. We could then guide the robots to open water using an acoustic communications link.
You had two robots -- why? What was different between them?
The two robots, Puma and Jaguar, are similar in design but feature different science sensor payloads. Puma's name comes from the phrase "PlUme MApper", which describe's its purpose pretty well. Hydrothermal vents typically have a sort of 'mushroom-cloud' shaped plume of chemical-rich water eminating from them which reaches to several hundred meters above the seafloor. To locate a vent, Puma first attempt to locate the main 'cloud' using a variety of chemical sensors, and then works to localize the stem of the cloud. This gives a basic idea of the vent's location. Jaguar is then deployed to capture photographic and microbathymetric sonar maps of the seafloor and get a 'close-up' view.
Any favorite stories from the trip?
Seeing polar bears was a pretty amazing experience, but one particularly amusing moment occurred after a dive when we were using a helicopter to survey in the AUV's location. We were coming to the end of our survey, and believed we had tracked down the position of the AUV under the ice. As we were flying back to the ship to find out where the survey placed the vehicle, we flew directly over the vehicle! It was sitting on the surface in an area of open water.
What have you been doing with Puma and Jaguar since this cruise?
I just returned from another trip with Puma and Jaguar, where we tested new navigation techniques for the robots. We hope these techniques will eventually allow us to do cooperative missions with both AUVs in the water at the same time, and without deploying navigation beacons beforehand, which could open up a variety of new types of missions.
Many thanks to Chris for taking the time to answer my questions! There are lots more pictures from the cruise on WHOI's website -- check them out and take a look at some of the scientific briefs available that talk more about the project's goals.
All photos for this post copyright 2007 -- Chris Murphy