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Frequently Asked Questions about ABE

Source: Ocean Instruments

What is ABE and why do we use it?

ABE is a robotic vehicle that can be programmed to explore the ocean and map the deep-sea floor to depths of 5,000 meters (3 miles). ABE carries no pilot, so it’s not limited by an air supply and can stay at work deep below the surface for days at a time before its batteries run out.

During such extended stays, ABE can map the sea floor with unprecedented detail, picking out objects smaller than a meter (3.3 feet) in size. ABE’s maps have been instrumental in finding new hydrothermal vents. The vehicle also takes digital photographs of the sea floor which ecologists use to identify deep-ocean life. Geologists use ABE's magnetic readings to understand the evolution of the sea floor ocean crust.

ABE stands for Autonomous Benthic Explorer. It is one example of a class of instruments called Autonomous Underwater Vehicles (including REMUS and the Spray glider) that are  revolutionizing ocean explorations. These instruments operate by themselves according to a computer program and input from their own sensors, making them much less expensive and more versatile than traditional manned expeditions.

How does ABE move around?

ABE reaches its working depth by sinking through the water attached to a heavy diving weight. Once at depth, ABE releases the diving weight and becomes neutrally buoyant. Five slender propellers combine to move ABE forward, backward, up and down. When its mission is over, the vehicle drops another weight (the “ascent weight”) and floats to the surface.

A network of computers control where ABE goes according to a mission program that engineers load into memory before the dive. Once ABE leaves the ship, it is responsible for its own navigation. Engineers on the ship can only listen in as ABE reports its progress, or send an emergency signal for ABE to return to the surface.

Although there’s no one piloting, the vehicle does know how to check its position and stay on course. Onboard sensors tell ABE how deep it is and how far off the bottom it is. And ABE calculates its location by contacting a system of acoustic transponders set out in fixed locations ahead of time.

How does ABE map the sea floor?

ABE follows a pattern of back-and-forth passes over its survey area, like a lawnmower over a lawn. The mission program either specifies a constant depth for these passes or tells ABE to stay a constant distance above the sea floor, usually 50 to 200 meters (165 to 660 feet).

A multibeam sonar records the shape of the sea floor under each pass. The sonar maps a swath about twice as wide as ABE's height above the sea floor.  This means ABE covers more area when it flies high, but it makes less-accurate maps than on low passes.  Scientists decide how high ABE should fly depending on the degree of detail they need and the amount of time they have.

ABE's magnetic readings combine with these topographic data to map the age and thickness of sea floor lava flows.

A more technical overview of ABE's mapping capabilities

What else can ABE sample?

ABE photographs the sea floor using video cameras mounted in the upper pontoons and a strobe light in the tail. On photographic surveys ABE flies much lower than during mapping missions, around 5 meters (16 feet) above the sea floor.

ABE's digital cameras were upgraded in 2006 to record 12-bit information on each pixel. The extra information allows researchers to process images and recover detail even under poor lighting conditions.

As ABE moves along at about 65 cm per second (1.5 mph), sensors record temperature, salinity and sea floor magnetism. Another instrument measures optical backscatter, a measure of the water’s cloudiness that helps ABE know when it has flown through a plume of warm water and ash from a hydrothermal vent.

ABE can bring back small samples of rock from the sea floor. ABE uses its thrusters to press a circular wax sampling pad firmly into the bottom, where the wax captures any loose shards.

Why does ABE look like the Starship Enterprise?

The resemblance to Captain Kirk’s spaceship is entirely coincidental, but it’s still worth explaining why ABE looks the way it does.

ABE’s odd, three-hulled design was invented to make the vehicle very good at its main purpose: making high-resolution maps of the sea floor. To record at such detail, ABE’s sensors need to remain stable even in churning deep-sea currents.

Engineers put most of ABE’s flotation in the top two pods, then suspended the heavy instruments and other gear in the bottom pod. The separation of buoyancy and mass makes ABE extremely resistant to pitching (forward and backward) and rolling (side-to-side). The design also places ABE's vertical thrusters safely in the space between the three pods.

ABE’s design team did stencil “NCC 1701” - the Enterprise’s registry number - on the hull, providing evidence that life can imitate art and that engineers do have senses of humor.

What have we learned using ABE?

Since its launch in 1996, ABE has made more than 150 dives, surveying an average of 16 km (10 miles) per dive. In addition to mapping and photographing the sea floor, ABE has sniffed out new hydrothermal vents in the Atlantic and Pacific Oceans,  measured the magnetism of sea floor lava flows and helped scientists describe sea floor ecosystems.

ABE's part in discovering the Rose Bud vent site, in 2002, is a good example of its capabilities. While ABE skimmed 40 meters above the sea floor on a mapping mission, its temperature sensor reported a plume of water that was just 0.02 degree C (0.036 degree F) warmer than its surroundings. Additional surveys followed the plume to its previously undiscovered source.

What platforms are involved?

Most research ships have the capability to carry and launch ABE. They need enough deck space to hold ABE’s cargo container and a crane that can lower ABE overboard and haul it back on deck after the mission. Ships must also be able to deploy and operate acoustic transponders, because ABE can't navigate outside of an acoustic transponder network.

Advantages

Although ABE is an expensive piece of technology, it is a much cheaper and more efficient way of surveying the deep ocean than by sending down a manned submersible or making long, repeated tows from a ship. And while ABE is conducting its mission, scientists can use the ship to do other research in the area.

ABE produces the most detailed maps of the sea floor yet made. Its computer system allows scientists to program complicated missions including instructions about how to react to conditions it encounters when it’s alone at depth.

ABE's five thrusters and great stability make ABE highly maneuverable. Something of an undersea helicopter, ABE can hover, cruise in any direction, make tight turns and stop on a dime.

Limitations

As of early 2006, work is nearing completion to allow ABE to share its transponder network with other vehicles like Jason or Alvin. Until then, dives with these three vehicles have to be made one after another instead of simultaneously.

Sources

Al Bradley, Principal Engineer, Applied Ocean Physics and Engineering, WHOI.

Dana Yoerger, Associate Scientist, Applied Ocean Physics and Engineering, WHOI.

Dan Fornari, Senior Scientist, Geology and Geophysics, WHOI.

Bellingham, J. Autonomous underwater vehicles (AUVs). p. 212-216 in J. H. Steele, K. K. Turekian and S. A. Thorpe (eds.), Encyclopedia of Ocean Science, Academic Press, San Diego, CA. (2001)

Jakuba, M., D. Yoerger, A. Bradley, C. German, C. Langmuir and T. Shank. Multiscale, multimodal AUV surveys for hydrothermal vent localization. Fourteenth International Symposium on Unmanned Untethered Submersible Technology (UUST05), Durham, NH. (2005)

Shank, T., D. Fornari, D. Yoerger, S. Humphris, A. Bradley, S. Hammond, J. Lupton, D. Scheirer, R. Collier, A.-L. Reysenbach, K. Ding, W. Seyfried, D. Butterfield, E. Olson, M. Lilley, N. Ward and J. Eisen. Deep submergence synergy: Alvin and ABE explore the Galapagos Rift at 86 W. Eos 84:425, 432-433. (2003)