How ABE works

	Enlarge ImageFigure 1. ABE descends in a spiral pattern to reach a specified point on the seafloor using minimal power. After reaching the bottom, ABE executes a series of tracklines while following the seafloor at a prescribed height.
	Enlarge ImageFigure 2. This plots shows ABE tracklines for three dives on the Explorer Ridge [Embley2002]
	Enlarge ImageFigure 3. This plot shows the multibeam bathymetric map made from the dives shown in figure 2.

ABE operates autonomously from the vessel. It has no tether, is controlled in real-time by onboard computers, and uses batteries for its power.

After launch, ABE descends to the seafloor through the use of a descent weight. Throughout the dive, ABE uses acoustic long-baseline transponder navigation and, when available, bottom-lock acoustic doppler measurements to determine its position and velocity. ABE descends in a controlled spiral trajectory to ensure that it reaches the desired starting point while consuming minimal energy.

After reaching the seafloor and performing a series of checks, ABE releases its descent weight to become neutrally buoyant and begins its survey. A dive can consist of a mix of hydrothermal plume survey at constant depth, sonar and magnetics survey following the seafloor (typically at a height of approximately 50-200 meters), and digital photography at a height of about 5 meters. ABE usually surveys until its batteries are depleted (between 15 and 30 hours depending on sensor payload and terrain). At the end of its dive, ABE releases its ascent weight to become positively buoyant and returns to the surface.