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Deep Submergence Vehicles
From: Woods Hole Oceanographic Institution
| By:
Rick Chandler |
EDITOR'S INTRODUCTION |
The vehicles of the National Deep Submergence Facility and their autonomous cousins transport both humans and a virtual "human presence" to the remote seafloor. They are invaluable assets to the research of scientists at the Woods Hole Oceanographic Institution (WHOI) and other research institutions. Whether diving more than 14,000 feet below the surface or remaining submerged for several days at a time, each of the vehicles described in this feature offers scientists unique tools to explore the mysteries beneath the ocean's surface.
The National Deep Submergence Facility operated by the Woods Hole Oceanographic Institution (WHOI) comprises Atlantis, a research vessel and support ship for the Deep Submergence Vehicle (DSV) Alvin; Alvinitself; the remotely operated vehicle system Jason/Medea and towed vehicles Argo II and DSL-120A. This feature describes the National Deep Submergence Facility vehicles as well as other WHOI-developed and -operated vehicles. |
 he vehicles operated by the Woods Hole Oceanographic Institution take scientists or a "scientific presence" into the deep sea to observe, sample and conduct experiments. |
<I>Alvin</I>
WHOI operates the US Navy-owned Deep Submergence Vehicle (DSV) Alvin as a national oceanographic facility.
A typical eight-hour dive takes two scientists and a pilot as deep as 4,500 meters (14,764 feet). When working at maximum depth, it takes about two hours for the sub to reach the seafloor and another two to return to the surface. The four hours of working time on the bottom are crammed with carefully planned photography, sampling and experiments. Alvin can hover, maneuver in rugged topography or rest on the bottom. |
Three 12-inch-diameter viewports allow scientists to observe the seafloor directly, and three video cameras mounted on Alvin's exterior record a wider view. Because there is no light in the deep sea, the sub carries metal-halide lights to illuminate the bottom. Two hydraulic, robotic arms manipulate sampling and experimental gear specially designed to work with their grasping "hands." |
A sample basket or sled mounted on the front of the sub can carry a variety of instruments. Scientists using the sub can bring up to 1,000 pounds of their own gear that may include sediment corers, temperature probes, water samplers and biological sample pumps. |
Alvin has made more than 3,800 dives for a wide variety of scientific endeavors. The sub's most famous exploits include locating a hydrogen bomb accidentally dropped into the Mediterranean Sea in 1966, exploring deep-sea hydrothermal vents discovered some two decades ago and surveying the sunken ocean liner Titanic. |
<I>Jason/Medea</I>
Jason/Medea is a remotely operated vehicle (ROV) system designed by the Institution's Deep Submergence Laboratory for scientific investigation of the deep ocean and seafloor. It is a dual vehicle system, with Medea serving in a tether management role that decouples Jason from surface motion. |
The Jason/Medea system offers wide area survey capabilities with Jason as a precision multi-sensory imaging and sampling platform. Both Medea and Jason are designed to operate to a maximum depth of 6,500 meters (21,450 feet). They are transportable and can be operated from a variety of vessels. The first Jason, introduced in 1991, was replaced in 2002 with a more powerful and versatile version of the vehicle. |
Movements of the support ship maneuver Medea utilizing dynamic positioning. Jason is propelled by seven DC electric thrusters that provide excellent passive stability in pitch and roll. Jason is designed for detailed survey and sampling tasks that require a high degree of maneuverability. It weighs about 7,800 pounds
(3,545 kilograms) in air but is nearly neutrally buoyant at depth. Jason's dynamic design makes it a very controllable platform. |
Jason is equipped with sonar imaging as well as video, still, and electronic cameras and appropriate lighting gear. It carries precision navigation equipment and sensors for depth, vehicle attitude (tilt), and altitude from the seafloor. Jason's manipulator can collect samples that may be put in a small basket attached to the vehicle or, for heavier items, on an "elevator" platform that carries them to the surface. Nine engineers and technicians from WHOI's Deep Submergence Operations Group operate the system at sea, and six 20- x 8-foot containers known as "vans" travel with Jason/Medea to serve as workshops and control rooms for seafloor operations. |
<I>ABE</I>
ABE, the Autonomous Benthic Explorer, is the first of its kind. ABE was born of scientists' frequent need to monitor an area over long periods of time, which is very expensive when using a surface ship for repeated visits with Alvin or Jason. ABE is a true robot, able to move on its own with no pilot or tether to a ship.
It is designed to perform a predetermined set of maneuvers to take photographs and collect data and samples within an area about the size of a city block. Currently, ABE is deployed for less than 24 hours at a time, but eventually the robot's designers expect that during long deployments, ABE will "sleep" at a docking station between data excursions, conserving power so it can work for months at a time. |
ABE was developed by a team of engineers as a true robot, with its own muscles (thrusters), nerves (cabling and power to operate the motors, cameras, and sensors), and brain (computer systems for powering up and down and for determining where to go and when to make measurements). Each of these components presented a complex design challenge. |
Currently, ABE follows a set of instructions placed in its memory before deployment and is recovered for data download following an excursion. However, its developers envision the not-too-distant day when ABE will be on station for long periods, and underwater acoustic transmission systems now being developed will allow scientists anywhere in the world to receive video and data from the robot and to control its movement and measurements from their home laboratories. |
<I>REMUS</I>
REMUS, or Remote Environmental Monitoring UnitS, is a low-cost autonomous underwater vehicle (AUV) developed by WHOI's Oceanographic Systems Laboratory for coastal monitoring and multiple-vehicle survey operations. |
The strength of the torpedo-shaped REMUS is its versatility. REMUS can be operated in fresh or salt water, in open ocean or narrow channels (even urban underground tunnels in one instance). Because REMUS is so small, it can be easily transported by compact car or shipped by air as baggage. Designed to be lightweight, it can be launched and recovered from a small vessel without special handling equipment. Despite its diminutive size, REMUS is configured to support a wide variety of sensor packages, allowing methodical sampling of key ocean characteristics such as temperature, currents, salinity, fluorescence, turbidity and water depth. The vehicle is particularly well suited to surveying and mapping tasks, with a 40-nautical-mile track taking about 10 hours. For ease of use by different experimenters, the REMUS control computer is compatible with PC technology and the vehicle user interface is designed to run on a laptop.
REMUS carries a sophisticated acoustical system. To determine its position, REMUS transmits a coded ping to a transponder and listens for a reply. The range and bearing of the reply allows REMUS to determine its location. By setting the transponders once using the Global Positioning System, a known track line can be followed on mission after mission. This system has been used to autonomously dock the vehicle. |
Towed vehicles
Oceanographers employ towed vehicles for a wide variety of measurement and surveying purposes. The two described here are part of WHOI's National Deep Submergence Facility. |
<I>Argo II</I>
Towed sleds, like Argo II, allow researchers to cover a great deal of ground in lowerings that may last for several days. Argo II carries video cameras, 35-mm and electronic still cameras, and several different acoustic sensors. It can be operated around the clock as deep as 20,000 feet, sending acoustic and video signals via fiber-optic cable to a shipboard control center, where five technicians fly the vehicle, record data and monitor equipment. The resulting suite of data, which may include 100,000 still images and 200 gigabytes of information, requires many months of analysis following the cruise. |
<I>DSL-120A</I>
DSL-120A is an underwater vehicle that is tethered to the ship by a long fiber-optic cable. Scientists use DSL-120A to map underwater terrain. However, instead of using light to map the bottom, it uses sound. |
The DSL-120A is equipped with two side-scan sonars--one that maps to the right, and one that maps to the left. Each sonar has one transducer that sends sound waves to the ocean floor once every 0.8 seconds, and two receivers that catch the echoes. The sonars gather two types of information. First, they measure the intensity of the returning signal. Just as a tennis ball bounces higher off of a driveway than off of the soft grass, the sound waves bounce harder off of hard surfaces than soft surfaces. Second, the sonar measures the bathymetry or contours of the surface it is mapping. Here is where the two receivers come into play. When the transducer bounces a signal from a flat area, the echo should reach the two receivers at the exact same time. If, however, the transducer bounces the signal off a slope, the echo returns at a different angle and reaches one of the receivers before the other. The time interval between when the echo reaches the first receiver and the second receiver is called the phase shift. The length of the phase shift depends on the slope. |
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