The artificial fish of the Venice lagoon

The European H2020 Subcultron project was completed in November 2019 and successfully deployed an autonomous fleet of underwater robots in the Venice lagoon. After four years of work, the research consortium  — which includes IMT Atlantique ­— has demonstrated the feasibility of synchronizing a swarm of over one hundred autonomous units in a complex environment. An achievement made possible by the use of robots equipped with a bio-inspired sixth sense known as an “electric sense.”

Curious marine species inhabited the Venice lagoon from April 2016 to November 2019. Nautical tourists and divers were able to observe strange transparent mussels measuring some forty centimeters, along with remarkable black lily pads drifting on the water’s surface. But amateur biologists would have been disappointed had they made the trip to observe them, since these strange plants and animals were actually artificial.  They were robots submerged in the waters of Venice as part of the European H2020 Subcultron project. Drawing on electronics and biomimetics, the project’s aim was to deploy an underwater swarm of over 100 robots, which were able to coordinate autonomously with one another by adapting to the environment.

To achieve this objective, the scientists taking part in the project chose Venice as the site for carrying it out. “The Venice lagoon is a sensitive, complex environment,” says Frédéric Boyer, a robotics researcher at IMT Atlantique — a member of the Subcultron research consortium. “It has shallow, very irregular depths, interspersed with all sorts of obstacles. The water is naturally turbid. The physical quantities of the environment vary greatly: salinity, temperature etc.” In short, the perfect environment for putting the robots in a difficult position and testing their capacity for adaptation and coordination.

An ecosystem of marine robots

As a first step, the researchers deployed 130 artificial mussels in the lagoon.  The mussels were actually electronic units encapsulated in a watertight tube. They were able to collect physical data about the environment but did not have the ability to move, other than sinking and resurfacing. Their autonomy was ensured by an innovative charging system developed by one of  the project partners: the Free University of Brussels. On the surface, the floating “lily pads” powered by solar energy were actually data processing bases. There was just one problem: the artificial mussels and lily pads could not communicate with one another. That’s where the notion of coordination and a third kind of robots came into play.

In the turbid waters of the Venice lagoon, artificial fish were responsible for transmitting environmental data from the bottom of the lagoon to the surface.

To send information from the bottom of the lagoon to the surface, the researchers deployed some fifty robotic fish. “They’re the size of a big sea bream and are driven by small propellers, so unlike the other robots, they can move,” explains Frédéric Boyer. This means that there is only a single path for transmitting data between the bottom of the lagoon and the surface: the mussels transmit information to the fish who swim towards the surface to deliver it to the lily pads, and then return to the mussels to start the process over again.  And all of this takes place in a variable marine environment, where the lily pads drift and the fish have to adapt.

Fish with a sixth sense

Developing this autonomous robot ecosystem was particularly difficult . “Current robots are developed with a specific goal, and are rarely intended to coordinate with other robots with different roles,” explains Frédéric Boyer. Developing the artificial fish, which played a crucial role, was therefore the biggest challenge of the project. The IMT Atlantique team contributed to these efforts by providing expertise on a bio-inspired sense: electric sense.

“It’s a sense found in certain fish that live in the waters of tropical forests,” says the researcher. “They have electrosensitive skin, which allows them to measure the distortions of electric fields produced by themselves or others in their immediate environment: another fish passing nearby causes a variation that they can feel. This means that they can stalk their prey or detect predators in muddy water or at night.” The artificial fish of the turbid Venice lagoon were equipped with this electric sense.

This capacity made it possible for the fish to engage in organizational, cooperative behaviors. Rather than each fish looking for the mussels and the lily pads on their own, they grouped together and travelled in schools. They were therefore better able to detect variations in the electric field, whether under the water or on the surface, and align themselves in the right direction. “It’s a bit like a compass that aligns itself with the Earth’s electromagnetic field,” says Frédéric Boyer.

The Subcultron project therefore marked two important advances in the field of robotics: the coordination of a fleet of autonomous agents and equipping under-water robots with a bio-inspired sense. These advances are of particular interest for monitoring ecosystems and the marine environment. One of the secondary aims of the project, for example, was tracking the phenomenon of oxygen depletion in the water of the Venice lagoon. An event that occurs at irregular intervals, in an unpredictable manner, which leads to local mortality of aquatic species. Using the data they measured, the swarm of underwater robots successfully demonstrated that it is possible to forecast this phenomenon more effectively. In other words, an artificial ecosystem for the benefit of the natural ecosystem.

Learn more about Subcultron

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The Subcultron project was officially launched in April 2015 as part of the Horizon 2020 research program . It was coordinated by the University of Graz, in Austria. It brought together IMT Atlantique in France, along with partners in Italy (the Pisa School of Advanced Studies, and the Venice Lagoon Research Consortium), Belgium (the Free University of Brussels), Croatia (the University of Zagreb), and Germany (Cybertronica).

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