Explore the Deep Sea
Tools & Techniques
Autonomous Benthic Explorer
Multi-purpose underwater robot
ABE is a robotic undersea vehicle that can be used to:
- Map the shape of the seafloor using sonar
- Take digital photographs
- Measure characteristics of seawater, such as pressure, temperature, chemical composition and movement relative to the seafloor.
No human driver, just a preloaded computer program
ABE operates completely on its own, using a computer program loaded before launch. The program gives ABE a systematic route to follow (usually a to-and-fro set of overlapping straight-line tracks), together with instructions about how to follow the seafloor:
- At a specific depth (it can determine water depth by measuring pressure), or
- At a specific distance above the seafloor (it uses sonar to determine its height)
To make a sonar map, ABE "flies" between 20 and 100 m (~65-330 feet) off the bottom of the ocean. To photograph the seafloor, it "flies" lower: about 5 m (~16 feet) above the seafloor.
How does it know where it is?
To do its job effectively, ABE needs to know its precise direction and location at all times. It carries an electronic compass to determine its direction, but determining its position is more difficult. Before ABE is launched, acoustic transponders (sound beacons) are dropped onto the seafloor, and their exact position is determined. During a dive, ABE "interrogates" those transponders, measuring the time it takes for a pulse of sound to travel from the vehicle, to the transponder, and back to the vehicle. Since the speed at which sound travels through water is a constant we know, the time measurement tells ABE the distance to the transponder. From two or more such measurements, ABE can determine its position. ABE fixes its position every 10 seconds for the entire dive, and uses the computed positions to stick to its pre-programmed route.
What happens during a dive?
First, researchers devise a dive plan to tell ABE which portion of the seafloor it should cover, the track it should follow and when it should use particular sensors. Before it is loaded into ABE, the dive plan is tested to ensure there are no programming errors. Next, the ABE team performs systems checks: they make sure all thrusters spin, all sensors are working, and the computer system is properly configured. Then, it's launch-time.
During launch, ABE is picked up with the ship's crane and lowered over the side. Heavy weights carry ABE to the bottom; this can take several hours. During the descent, ABE computes its position and points itself toward the desired starting spot for the survey, conserving battery power as much as possible.
After reaching the seafloor, ABE performs a series of checks, and then heads off on its planned tracklines. It follows the tracks for many hours (up to 30). When ABE's batteries are depleted, it stops, drops another set of weights, and rises to the surface. The ship's crew takes a small boat out to ABE as it floats on the surface. A member of the ABE team in the boat then drives ABE back to the ship using a radio control joystick (much like a remote control car or boat). When the ship is close enough, a line is hooked onto ABE, and it is lifted back on deck using the ship's crane.
What happens after a dive?
After ABE is lifted on-board, its data files are downloaded and its batteries recharged—a process that can take around 14 hours. Then it's time to review the data files, assemble maps, and do it all again.
In a hectic expedition schedule, there's not much time to rest! Once the maps from the first dive are complete, it's time to plan the next dive.