Autonomous underwater vehicles (AUVs) play a valuable role in the maintenance and observance of our oceans, seas, rivers and lakes to ensure safety to our most valuable natural resources, as well as provide assistance to the divers who perform important tasks within the depths of our largest bodies of water.
India is looking to expand research and development work on underwater vehicles and intends to develop long-endurance AUVs for commercial and defence applications in the near future. While there is significant growth in the sector, not many people are aware about the functionalities of AUVs and what their advantages are.
IEEE Senior Members Roberto Petroccia, Fausto Ferreira and Gabriele Ferri, who are also members of the IEEE Oceanic Engineering Society (OES), gave their insights on AUVs. They currently work at the NATO Science and Technology Organization Centre for Maritime Research and Experimentation in La Spezia, Italy.
“AUVs can work for a long time without getting tired and at depths impossible for a diver,” Ferri said. “Divers can operate typically up to 60 meters, requiring use of special gases and tools when operating at higher depths. Additionally, the time they can spend at such a high depth is quite limited. However, the sea bottom goes much deeper (up to 11,000 meters) and many installations are below the operating depth of divers, such as oil rigs or communications pipelines.”
Essentially, vehicles and sensors are capable of covering and collecting data in larger areas, at greater depths and at quicker speeds than human divers and researchers. Plus, the deployment of a swarm of long-range and long endurance AUVs are capable of collecting environmental measurements without impacting marine life, says Ferreira.
“These systems of new generation can increase the spatial and temporal scale of the monitoring and can provide the persistence and synopticity (measurements at different locations at the same time),” says Petroccia. “This is crucial for understanding the state of the sea and for tracking ongoing phenomena, such as an oil spill or an algal bloom.”
This important type of research is only possible through the use of AUVs because surface ships and oceanographic observatories can only collect measurements in a single point.
To further their sustainability efforts through passive data collection, technologists who create AUVs often draw their creative designs from nature itself. “Many designs mimic marine life, such as jellyfish or fish, to optimize the efficiency of navigation taking inspiration by nature,” says Petroccia. “Other shapes, such as octopus have become a source of inspiration to support manipulators that are able to work without damaging the marine ecosystem, such as when working in the coralline reefs or when monitoring clams.”
How does an autonomous underwater vehicle work?
When we think of autonomous technology, the first thing that comes to mind is often a vehicle found on the highway. While some of the technologies are similar to a car, AUVs must have a complex system because of the hostile environment the robot must endure in the water.
“Global navigation satellite system (GNSS) is not available [underwater]”, says Ferreira. “This makes underwater robot self-localization challenging and still an open issue in the research community. Doppler velocity logs can measure the speed of the robot with respect to the seafloor, but only when the robot is not navigating too high from the bottom.”
Another difference of an AUV from an autonomous car is that a gasoline or diesel engine cannot be submerged underwater because of the lack of oxygen. Ferri explains that this challenge has actually pushed technologists to turn to cleaner propulsion technologies, “such as fuel cells that increase their endurance with respect to typical lithium batteries.”
Technologists also face the challenge of efficient communication and sensing underwater. Their reliable solution is to utilize the acoustics underwater. “Acoustic communications enables us to exchange data over long distances (up to tens of kilometers) but with a low data rate (typically few hundreds of bits per second or up to few kilobits per seconds) and long propagation delays,” says Petroccia. “This is very different with respect to what is experienced in terrestrial wireless radio networks, requiring to design novel communications solutions and networking protocols. This dictates that AUVs need to become more and more autonomous to accomplish their missions, since a direct and reliable link with a pilot cannot be guaranteed.”
AUVs are keeping our oceans clean and spill-free
The gas and oil industry is beginning to tap into the technology and advantages of AUV monitoring, inspection, maintenance and even intervention in reducing chemical and oil spills in our oceans.
“Several solutions have been proposed to allow AUVs following in an autonomous way along pipelines on the seabed, thus inspecting the thickness and status of the pipes, and detecting possible leakage of oil and gas,” says Ferri. “Additionally, there is a growing interest in deploying resident subsea systems which are capable of inspecting, maintaining and repairing the required equipment.”
AUVs and marine robots are also capable of helping during the oil clean-up process as well. “Oil tends to submerge with the passing of time,” says Ferreira. “AUVs can follow the plume, study the phenomena and localize the leak source. For instance, one expedition characterized subsurface oil plumes extending from the Deepwater Horizon (the massive accident that happened in the Gulf of Mexico in 2010) using novel technology and the latest in biogeochemical techniques.”
