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Frequently Asked Questions about ABE

 On this page:
-What is ABE and why do we use it?
-How does ABE move around?
-How does ABE map the sea floor?
-What else can ABE sample?
-Why does ABE look like the Starship Enterprise?
-What have we learned using ABE?
-What platforms are involved?
-Advantages
-Limitations
-Sources
  
ABE goes overboard
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ABE, the Autonomous Benthic Explorer, heads overboard. Once in the water, it will descend at about 1 km per hour (0.6 mph). When it reaches the sea floor, it will begin detailed mapping. (photo by Woods Hole Oceanographic Institution)
ABE begins descent to sea floor
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Once in the water, ABE begins its fall to the sea floor. Thrusters periodically kick on to point ABE toward its target on the bottom, but most of the descent uses gravity, not batteries. The vertical thrusters (visible between the two red pods) are used only at depth to push ABE over ridges and pinnacles. (photo courtesy Dan Fornari, WHOI)
ABE scientist Al Bradley in his office
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Al Bradley, one of ABE's designers, surrounded by ABE models in his office. (photo by Tom Kleindinst, WHOI)
The principal designers look ABE over on the WHOI dock
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Al Bradley and Dana Yoerger, two of ABE's principal designers, give it the once-over on the WHOI dock. (photo by Tom Kleindinst, WHOI)
Related Links
» The ABE Web site
» ABE Slideshow
Get a glimpse inside ABE, from the WHOI Dive and Discover website.
» Paving the Seafloor?Brick by Brick
ABE's detailed maps and magnetic readings help WHOI scientist Maurice Tivey understand deep-sea lava flows. (From Oceanus magazine)
» Realizing the Dreams of Da Vinci and Verne
More on ABE and the rest of the AUV fleet at Woods Hole, from Oceanus magazine.
» NOAA's Ocean Explorers - ABE
NOAA's write-up of ABE, its specifications and uses.
» Visions 2005: Operations
University of Washington
  
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)


ABE's original trackline, detected clusters, and nested survey (in green)


ABE Gets Bloodhound Lessons

With "automated nested sampling," ABE sniffs out vents on the fly

The time-honored way of finding hydrothermal vents is to criss-cross an area in a research vessel, towing mapping instruments near the bottom and periodically stopping to lower a CTD. Scientists on deck assemble the data as it arrives and look for clues that a vent is near.

This method is the only practical way to detect vents amid large swaths of ocean. But when it comes to homing in on an exact location, instruments towed on miles-long cables don't maneuver well and their positions are hard to pinpoint. The odds of dropping a CTD directly onto a vent plume aren't good, either.

But after dozens of finds and a decade of experience, ABE's operators are beginning to program ABE with their expertise and send it down to hunt for vents. On three consecutive dives, the scientists narrow ABE's search program to focus on the most promising areas, eventually scheduling ABE to make low passes and take photographs.

In a recent innovation, called automated nested surveying, ABE does some of the search narrowing on its own. On a single dive ABE combs through its data, picks out telltale signs of vent activity and alters course to investigate. In 2005, ABE used the new technique to find several vents in the Lau Basin of the southwest Pacific Ocean and along the Southern Mid-Atlantic Ridge.

On one dive, ABE’s operators dedicated 5 percent of dive time to an automated nested survey, during which ABE netted an extra 96 out of 265 total high-quality photos of vent areas.

Searching for smokers in the dark
That’s harder than it sounds, considering the circumstances. ABE’s job is a lot like dropping in to a strange city at midnight and trying to find the chimneys. The ocean is pitch-black and cold, and ABE has only a few sensor readings - water temperature, cloudiness and chemical makeup - to work with.

So ABE keeps a running tally of the most interesting readings and their locations as it travels a broad survey route. When it finds a more extreme reading ABE adds it to the list and drops the lowest one - like keeping a Top 10 list but with many more than ten items.

After ABE finishes the survey, it analyzes the locations on its list to identify clusters of extreme readings. Then it returns to the clusters and re-surveys the area in greater detail.

Redox potential has vent-finding potential
A newly installed chemical sensor is a key part of the search. Temperature and cloudiness are easy to measure, but they signal only that a vent is within a kilometer or so. (That’s because plumes of vent water rise a few hundred meters and then spread out horizontally, like smokestack emissions on a calm day.)

But vents also release rare compounds that react with sea water and quickly convert into other forms. A sensor developed by Ko-ichi Nakamura and loaned to the ABE crew measures this quality, called redox potential (or eH). Low eH values mean a vent is close, within a few hundred meters (500 feet or so).

ABE’s engineers continue to refine their software and make ABE smarter. Improvements in 2006 include combining sensor readings with measurements of current speed. So when ABE senses vent water high above the sea floor, it can calculate what area of ocean bottom the water came from.