This AUV runs on solar power. The amount of power available and the weight of the power source are major factors for AUV designers and users. Click image for larger view and image credit.
This sonar image of a shipwreck off Prudence Island in Rhode Island demonstrates why marine archaeologists are interested in using AUVs for their research. Click image for larger view and image credit.
View a video animation demonstrating how the sonar mounted on AUVs can quickly and accurately provide images of underwater objects.
What Are AUVs, and Why Are They Used?
Denise Crimmins
Engineer and Project Manager
Naval Undersea Warfare Center Division Newport
Justin Manley
Technology Goal Lead
NOAA Ocean Exploration and Research (Battelle)
At their most fundamental, autonomous underwater vehicles (AUVs) are simply computer-controlled systems operating undersea. They are considered autonomous because they have no physical connection to their operator, who may be onshore or aboard a ship. They are also self-guiding and self-powered.
Not long ago, AUVs looked and operated like torpedoes: they were long cylinders that kept moving. As technology improved, AUVs have become more complex and adopted a variety of new forms and functions. Now, AUVs can glide from sea surface to depths and back. Others can stop, hover, and move like blimps or helicopters do through the air. Solar-powered AUVs can spend a portion of their time at the surface, blurring the distinction between undersea and surface vehicles.
AUVs can operate in intertidal waters (between the limits of high and low tide), and some AUVs are designed to operate to 6,000 meters. The most advanced undersea system, which can reach the bottom of the ocean at 11,000 meters, is a special hybrid vehicle that includes an AUV mode. AUV systems can be small, easily portable vehicles under 100 pounds, or they can be long-endurance gliders or very large systems. The largest AUVs in service weigh thousands of pounds and require their own dedicated support vessels.
Fully autonomous operations carry power onboard. Power is needed in large part to move an AUV through the water with propellers or powering thrusters, and also to operate sensors onboard the AUVs. AUVs use more energy for their size and weight relative to above-water vehicles, like cars and airplanes; think about walking alongside a pool versus swimming a lap. Most AUVs use specialized batteries, although some AUVs have used fuel cells or rechargeable solar power. Certain AUVs, such as gliders, minimize energy demands by allowing gravity and buoyancy to propel them. Depending on the type of power and task at hand, AUVs can run for as short as hours or as long as days or even months before battery recharging is needed. AUV technicians are constantly thinking about extending battery life by reducing drag or making AUVs lighter.
Early AUVs were totally reliant on their onboard software for decision making, and until recently, undersea wireless communications were effectively impossible. Once an early AUV was launched, there was no opportunity to change its programming or otherwise alter its mission. At best, operators had a tracking system so they could observe where the AUV went. If it was on course, it could be very uninteresting; if it was not on course, not knowing the reason for the error and the inability to do anything about it provided some excitement and anxiety.
AUVs can be extremely maneuverable, as shown in this clip of the Hydrobatic UUV in a pool test site.
The Remus AUV demonstrating maneuverability in a pool test site.
The Transphibian, an AUV used by the Navy for mine identification and neutralization, is similarly nimble.
With improvements in acoustic systems, it is now possible to transmit small amounts of data between AUVs and their operators. Now vehicle status such as depth, battery level, and even some sensor data can be sent from the AUV to the mission control computer on shore or on a boat. Low-level decisions, such as “speed up” or “turn,” are made by the computer and software on the AUV, but operators can transmit higher-level decisions, like “stop” and “come home.” Operators can also change the survey area while an AUV is submerged. Even though AUVs may receive messages from an operator, the operator is not driving. This is an important distinction from remotely operated vehicles, which an operator can use a joystick to control.
Since the early 1990s, the Office of Naval Research has invested heavily in autonomous underwater vehicle (AUV) technology development for military purposes, including underwater mine hunting. In the last five years, the National Oceanic and Atmospheric Administration (NOAA) has been considering the role of AUVs in missions that include coastal survey, fisheries research, and ocean exploration. Pilot programs have used commercially available AUVs to evaluate their ability and performance in NOAA missions. With advancements in AUV technology, some are now available commercially. As they become more sophisticated, less expensive, and able to work together as a coordinated AUV fleet, their use will likely increase.
Already, AUVs are attractive options for ocean-based research. They can reach shallower water than boats, and deeper water than human divers or tethered vehicles. Once deployed and underwater, AUVs are safe from bad weather. They are also scalable, or modular, meaning that scientists can choose which sensors to attach to them, depending on their research objectives. AUVs are also much less expensive than research vessels, and can complete identical repeat surveys of an area.
Large AUVs typically carry very advanced instruments for imaging what is on and even below the seafloor. Allowing underwater robots to sense dangerous hazards, like live underwater mines, can save lives and property. Locating hazards or shipwrecks on or below the seafloor also makes AUVs of interest to the shipping industry and maritime archaeologists. The offshore oil industry can use the sensors to find the geological formations below the seafloor that make oil deposits more likely. Industries with underwater infrastructure, like pipes and cables, can use AUVs to identify areas that need repair.
Gliders outfitted with oceanographic sensors can measure the ocean’s conductivity, turbulence, pollutants, dissolved oxygen and temperature. This data can provide oceanographers with better information about ocean processes, like mixing; meteorologists with more data about weather events like El Niño and hurricanes; managers with more information about water quality; and climate modelers a better understanding of changes over time. Small AUVs can be equipped with unique sensors to study ocean phenomena, map coastal features like deep-water corals, and observe marine life. Some have suggested that AUVs can even help natural resource managers monitor the activity around protected areas, like shipwrecks, or marine reserves.
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