Sentry (AUV)
Deep-sea AUV for sampling, imaging, and mapping at 6,000 m.
The Sentry is an autonomous underwater vehicle (AUV) built by the Woods Hole Oceanographic Institution. It can descend to depths of 6,000 meters and carries various tools for collecting samples, images, and data from the deep ocean. Sentry replaces the earlier Autonomous Benthic Explorer (ABE) and is built for research in mid-water and near-seabed environments.
The vehicle is 6 feet tall, 7.2 feet wide (including thrusters), and 9.5 feet long. It is transported to its work site inside a container that holds all necessary operating systems. Communication and data reception can be handled from land or ship.
For navigation, Sentry uses a doppler velocity log combined with an inertial navigation system, along with a USBL or LBL acoustic navigation system. This same acoustic system also sends commands to the vehicle and receives data from its sensors and equipment. Four thrusters are attached to four tilting planes—similar to small wings—paired at the front and rear. Sentry can operate in hover mode (with control surfaces vertical) or forward flight mode (with surfaces angled between +45 and -45 degrees from horizontal), giving it six degrees of freedom for sensor measurements.
Direction and attitude are tracked with a TCM2 PNI sensor and a Systron Donner inertial yaw rate sensor. A 300 kHz RD Instruments Doppler sonar measures heading in 3D and altitude above the seafloor, while a Paroscientific depth sensor monitors depth below the surface. These systems achieve heading accuracy of half a degree and depth accuracy of 2 centimeters. Propulsion and control are handled by an onboard "Jason 2" system, developed by Woods Hole Oceanographic Institution and Johns Hopkins University, proven in hundreds of deep-water tests. Power comes from 1,000 lithium-ion batteries specially adapted for high pressure. Estimated range is 100 kilometers at 2.5 knots and 150 kilometers at 1.5 knots.
Sentry can carry a wide range of equipment. Standard sensors include a CTD (conductivity, temperature, depth) and digital cameras. It can also carry gear for bathymetric and magnetic mapping, the TETHYS in-situ mass spectrometer, and a Nakamura redox potential probe.
In one mission, Sentry mapped potential sites for an undersea observatory along the U.S. coast.
- Height
- 6 ft
- Width
- 7.2 ft (including thrusters)
- Length
- 9.5 ft
- Maximum depth
- 6,000 m
- Range
- 100 km at 2.5 knots; 150 km at 1.5 knots
- First deep-sea trial
- Off Bermuda in April 2006
Lore & Background
Sentry was first trialled in deep-sea operations off Bermuda in April 2006. It is carried to its work location in a container containing all systems necessary for operation. Communications can be established from land-based or ship-based locations for control and data reception. The vehicle navigates using a doppler velocity log combined with an inertial navigation system, used in conjunction with a USBL or LBL acoustic navigation system that also communicates with the vessel. Sentry is powered by four thrusters attached to four tilting planes, similar to small wings, attached in pairs at the front and rear. It has two modes of operation: hover mode, where control surfaces are vertical, and forward flight mode, where surfaces can be moved to +45 and -45 degrees from horizontal. These provide a 6-DoF capability to its sensors. Direction and attitude are tracked with a TCM2 PNI sensor and a Systron Donner inertial yaw rate sensor. A 300 kHz RD Instruments bottom-lock Doppler sonar measures heading in 3D and altitude above the sea floor, while a Paroscientific depth sensor monitors depth. These systems allow heading accuracy of half a degree and depth accuracy of 2 cm. Propulsion and control are managed by an onboard Jason 2 system developed by Woods Hole and Johns Hopkins University, proven over several hundred deep-water tests. The AUV is powered by 1,000 lithium-ion batteries designed for great pressure at depth.
Reader's Guide
Sentry has been used for significant scientific missions. It mapped possible sites for an undersea observatory along the US coast, with John Delaney of the University of Washington noting that the survey provided great precision and resolution, aiding installation of primary nodes on the Juan de Fuca tectonic plate. The survey was carried out in the Strait of Juan de Fuca between Washington State and Vancouver Island. Sentry also helped take 5,800 mass spectrometer readings at the site of the Deepwater Horizon explosion and subsequent oil spill in the Gulf of Mexico. It was sent 19 times into the underwater oil plume, using TETHYS and CTD sensors to provide data on chemical makeup and plume positions, with detection as low as 50 micrograms per litre. Its ability to carry standard sensors such as CTD and digital cameras, as well as equipment for bathymetric and magnetic mapping, the TETHYS in-situ mass spectrometer, and the Nakamura redox potential probe, makes it a versatile platform for deep-sea research.
Did You Know?
- It is the successor to the Autonomous Benthic Explorer (ABE).
- Sentry uses a Jason 2 system for propulsion and control, developed by Woods Hole and Johns Hopkins University.
- It was used to take 5,800 mass spectrometer readings at the Deepwater Horizon oil spill site.
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