A charging station for underwater robots has been installed on the seabed in a Norwegian fjord, and special training will ensure the robots can always find the shortest route to the power source.

Seven years ago, Trondheim fjord was declared the world’s first test site for autonomous vehicles and the Norwegian University of Science and Technology's (NTNU) largest laboratory describes it as an Eldorado for researchers developing underwater robots. NTNU is highly active in the development of robotics that operate under water, on the surface of the water and in the air, and the researchers make frequent use of the large ocean laboratory.

The robots have many uses, from mapping coral reefs and the geology of the seabed to inspecting maritime installations and mapping archaeological sites.

Recently, students, doctoral research fellows, researchers and partners from trade and industry took a trip aboard the research vessel Gunnerus, out on to the fjord, to see how some of the underwater robotics work. A robot measuring approximately 1 cubic metre, housed in an open crate, was loaded on board.

The vessel chugs towards its destination - a charging station located on the seabed. In 2022, the charging station was established not far from the isle of Munkholmen, at a depth of 350 metres. This station is a joint venture between NTNU and Norwegian energy company Equinor.

It has recently been moved a little closer to Trondheim Biological Station and is located close to another subsea installation belonging to Equinor. The robots can connect themselves to these stations when they need to top up their batteries.

This means it is important that the robots can find their way to the charging station – and as efficiently as possible.

The first underwater drone developed at NTNU is a snakelike robot called Eelume, based on technology developed by both NTNU and the SINTEF European research institute. Eelume is strongly inspired by how snakes and sea eels move through water.

Professor Kristin Pettersen is the brain behind the fully developed version of Eelume, which is now in production. Huge amounts of mathematical calculations form the basis of adaptations and efficiency improvements for the technology.

These snakelike robots are now being approved for use on the Åsgård oilfield in the Norwegian Sea. They will operate there as caretakers on the seabed, checking that the underwater installations are in order. When they are out checking and possibly repairing something, the robots use electricity, meaning they need to recharge between jobs.

On the demonstration trip, once Gunnerus has reached the correct position, the robot is slowly lowered into the sea. The goal is for it to find the charging station as efficiently as possible

A container standing on the deck is filled with powerful computers with large screens. Researchers, students and doctoral research fellows all pay close attention to the screens and monitor how the robot moves underwater when searching on its own for the charging station.

One of them is doctoral research fellow Gabrielė Kasparavičiūtė from the department of marine technology, she says, “A hypothetical scenario might be that there has been a leak at an installation, such as an oil platform. We would send down an autonomous underwater robot to examine the damage.

"The robot then has to check whether it has enough energy to reach the accident site, and it has to find the right algorithm to solve the task."

The robot’s journey towards the charging station takes time. Kasparavičiūtė has fed it algorithms that should give it a few extra challenges. The robot has to figure these out and ends up getting a hard, but useful workout.

“What we are testing and demonstrating here is a planning algorithm that enables the robot to choose a route to an inspection point," explains Martin Ludvigsen, professor at the department of marine technology, and one of the leading researchers in the field of underwater robotics. "The choice of route is based on how much activity or work it must perform, and this is then linked to how much energy the robot has at its disposal.”

A lot of work is being done in this research community to make the robots as autonomous as possible and able to make independent and smart choices. It involves a robot choosing which tasks it has the capacity to complete based on how much power it has left, finding the shortest route to the places it will conduct inspections, and calculating how much power it requires to return to the charging station.

The underwater robots have many applications, such as inspection of maritime installations like oil platforms, fish farms, quays and boat hulls. Underwater robots are also used to map the geology of the seabed and marine life, such as coral reefs.

Mapping marine life provides important information about environmental changes. The underwater robots are also used to transport measuring equipment and sensors used to collect data from the ocean.

They are also being used to investigate archaeological finds on the seabed and are being used in a major survey taking place at the bottom of Mjøsa, Norway’s largest lake; and to document the ship graveyard around the Norwegian arctic archipelago of Svalbard.