Sentry (AUV)
Encyclopedia
The Sentry is an autonomous underwater vehicle
(AUV) made by the Woods Hole Oceanographic Institution
. Sentry is designed to descend to depths of 4500 metres (14,763.8 ft) and to carry a range of devices for taking samples, pictures and readings from the deep sea.
Sentry is the successor to ABE (Autonomous Benthic Explorer) and is designed for research at the mid-water and near-seabed depths. The UAV was first trialled in deep-sea operations off Bermuda in April 2006.
Sentry is 6 feet (1.8 m) feet in height, 7.2 feet (2.2 m) wide (including thrusters) and 9.5 feet (2.9 m) long.
velocity log combined with an inertial navigation system. These are used in conjunction with a USBL, or LBL, acoustic navigation system
which is also used to communicate with the vessel—providing it with commands as well as receiving the data from the sensors and onboard equipment.
Sentry is powered by four thrusters attached to four "tilting planes", similar to small wings, attached in pairs at the front and rear of the vehicle. Sentry has two modes of operation, hover mode and forward flight mode. In hover mode the control surfaces are moved into a vertical position, and in forward mode the surfaces can be moved to +45 and -45 degrees from horizontal. Sentry uses these to give a 6-DoF
(degrees of freedom) capability to its sensors for measurement.
Sentry tracks its direction and attitude with a TCM2 PNI sensor and a Systron Donner Inertial yaw rate sensor. The doppler sonar, a 300kHz RD Instruments bottom-lock unit, measures the heading in 3D as well as altitude above the sea floor while a Paroscientific depth sensor monitors depth below the sea surface. These systems allow for an accuracy of 1/2 a degree in heading and to maintain depth to an accuracy of 2 centimetre (0.78740157480315 in).
Propulsion and control are managed by an onboard "Jason 2" system which was developed by the Woods Hole Oceanographic Institution and the Johns Hopkins University and proven over several hundred deep-water tests. The AUV is powered by 1,000 lithium-ion batteries designed and specially adapted for the great pressure at the depths that Sentry can descend to. It is estimated that Sentry will have a range of 100 km at 2.5 knots and 150 km at 1.5 knots.
(conductivity, temperature and depth) and digital cameras, as well as being able to carry equipment for bathymetric and magnetic mapping, the TETHYS (Tethered Yearlong Spectrometer) in-situ mass spectrometer and the Nakamura redox potential
probe.
The survey was carried out in the Strait of Juan de Fuca running between north-west Washington State and Vancouver Island, British Columbia, Canada, which links Puget Sound and the Strait of Georgia with the Pacific Ocean.
and subsequentoil spill
in the Gulf of Mexico. It was sent 19 times into the under-water oil plume
to provide data, using the TETHYS and CTD sensors, giving information on the chemical make-up and the positions of the plume. Detection was made as low as 50 micrograms per litre.
Autonomous Underwater Vehicle
An autonomous underwater vehicle is a robot which travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles...
(AUV) made by the Woods Hole Oceanographic Institution
Woods Hole Oceanographic Institution
The Woods Hole Oceanographic Institution is a private, nonprofit research and higher education facility dedicated to the study of all aspects of marine science and engineering and to the education of marine researchers. Established in 1930, it is the largest independent oceanographic research...
. Sentry is designed to descend to depths of 4500 metres (14,763.8 ft) and to carry a range of devices for taking samples, pictures and readings from the deep sea.
Sentry is the successor to ABE (Autonomous Benthic Explorer) and is designed for research at the mid-water and near-seabed depths. The UAV was first trialled in deep-sea operations off Bermuda in April 2006.
Sentry is 6 feet (1.8 m) feet in height, 7.2 feet (2.2 m) wide (including thrusters) and 9.5 feet (2.9 m) long.
Operation
The Sentry is carried to its work location in a container containing all the systems necessary for operation. Communications can be established from land-based or ship-based locations for control and data reception.Navigation
Sentry navigates by means of a dopplerDoppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
velocity log combined with an inertial navigation system. These are used in conjunction with a USBL, or LBL, acoustic navigation system
Underwater Acoustic Positioning System
An underwater acoustic positioning system is a system for the tracking and navigation of underwater vehicles or divers by means of acoustic distance and/or direction measurements, and subsequent position triangulation...
which is also used to communicate with the vessel—providing it with commands as well as receiving the data from the sensors and onboard equipment.
Sentry is powered by four thrusters attached to four "tilting planes", similar to small wings, attached in pairs at the front and rear of the vehicle. Sentry has two modes of operation, hover mode and forward flight mode. In hover mode the control surfaces are moved into a vertical position, and in forward mode the surfaces can be moved to +45 and -45 degrees from horizontal. Sentry uses these to give a 6-DoF
Six degrees of freedom
Six degrees of freedom refers to motion of a rigid body in three-dimensional space, namely the ability to move forward/backward, up/down, left/right combined with rotation about three perpendicular axes...
(degrees of freedom) capability to its sensors for measurement.
Sentry tracks its direction and attitude with a TCM2 PNI sensor and a Systron Donner Inertial yaw rate sensor. The doppler sonar, a 300kHz RD Instruments bottom-lock unit, measures the heading in 3D as well as altitude above the sea floor while a Paroscientific depth sensor monitors depth below the sea surface. These systems allow for an accuracy of 1/2 a degree in heading and to maintain depth to an accuracy of 2 centimetre (0.78740157480315 in).
Propulsion and control are managed by an onboard "Jason 2" system which was developed by the Woods Hole Oceanographic Institution and the Johns Hopkins University and proven over several hundred deep-water tests. The AUV is powered by 1,000 lithium-ion batteries designed and specially adapted for the great pressure at the depths that Sentry can descend to. It is estimated that Sentry will have a range of 100 km at 2.5 knots and 150 km at 1.5 knots.
Sensors, measurement and sampling
The equipment that can be carried by Sentry is extensive in range. The vessel carries standard sensors, such as CTDConductivity, temperature, depth
A CTD profiler is an essential instrument of physical and biological oceanographic field research. Operated from a ship, it greatly contributes to our understanding of ocean dynamics by gathering information on the distribution and variation of the ocean's properties...
(conductivity, temperature and depth) and digital cameras, as well as being able to carry equipment for bathymetric and magnetic mapping, the TETHYS (Tethered Yearlong Spectrometer) in-situ mass spectrometer and the Nakamura redox potential
Reduction potential
Reduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts , or millivolts...
probe.
Underwater observatory
Sentry was used to map possible sites for an undersea observatory along the US coast. John Delaney of the University of Washington said "Sentry has given us a survey with great precision and resolution. These maps will help with the installation of the primary nodes of a networked observatory on the Juan de Fuca tectonic plate".The survey was carried out in the Strait of Juan de Fuca running between north-west Washington State and Vancouver Island, British Columbia, Canada, which links Puget Sound and the Strait of Georgia with the Pacific Ocean.
Deepwater Horizon oil spill survey
Recently Sentry was used to help take 5,800 mass spectrometer readings in the sea at the site of the Deepwater Horizon explosionDeepwater Horizon explosion
The Deepwater Horizon drilling rig explosion refers to the April 20, 2010 explosion and subsequent fire on the Deepwater Horizon semi-submersible Mobile Offshore Drilling Unit , which was owned and operated by Transocean and drilling for BP in the Macondo Prospect oil field about southeast of the...
and subsequentoil spill
Deepwater Horizon oil spill
The Deepwater Horizon oil spill is an oil spill in the Gulf of Mexico which flowed unabated for three months in 2010, and continues to leak fresh oil. It is the largest accidental marine oil spill in the history of the petroleum industry...
in the Gulf of Mexico. It was sent 19 times into the under-water oil plume
Plume (hydrodynamics)
In hydrodynamics, a plume is a column of one fluid or gas moving through another. Several effects control the motion of the fluid, including momentum, diffusion, and buoyancy...
to provide data, using the TETHYS and CTD sensors, giving information on the chemical make-up and the positions of the plume. Detection was made as low as 50 micrograms per litre.