WiMUST, or Widely scalable Mobile Underwater Sonar Technology, is a project funded by the EU H2020 program, which started in 2015 and is now on its final stage. Besides several European partners from Italy, Germany, Holand, France and the UK, it features three Portuguese partners: Geosurveys of Aveiro, Cintal of University of Algarve and Instituto Superior Técnico, through the Dynamical Systems and Ocean Robotics Lab (DSOR) here at ISR-Lisboa, under the coordination of António Pascoal. The project developed work in the area of cooperative marine robots, with applications to seismic reflection mapping.
“This process is like performing an ultrasound to the bottom of the ocean. Its aim is to map not its shape – that’s called bathymetry – but what we can be found underneath the seabed.”
Luís Sebastião, one of the researchers involved in the project, explained that seismic reflection is currently used in several scales and contexts. “It can be used, for instance, to search for oil and gas deposits by using very powerful sound sources. The sound waves travel through the water column to the bottom, where they penetrate several layers of sediment. Arrays of hydrophones called streamers record the echoes from those layers, which allows for the 3D reconstruction of the geological features in the soil underneath the water.” Currently, this is a costly process, mostly in time and resources, since the streamers can reach 12km in length, something that greatly limits the manoeuvrability of the survey vessel and frequently calls for repetitive manoeuvres in order to reach complete coverage. Since these processes often need to be undergone in specific windows of time and certain natural conditions, a new technology was needed that would allow for more control, more flexibility and higher precision.
That is why WiMUST intended to develop a new breed of ultra-high resolution seismic mapping using robots to carry the sound sources and the streamers. Placing the streamers closer to the bottom allows for the ‘ultrasound’ to be done in even higher resolution, with less powerful sources of sound but with much superior demands in terms of positioning and reach. By varying the formation of the vehicles and their streamers the system behaves as an antenna, which can be adapted for different sites with different conditions.
“It’s necessary not only to know with great precision where the source of sound and hydrophones are but also to drive them precisely to where they should be in order to obtain a full coverage of the sea bottom. This technology makes sense for a number of activities, from civil engineering, where you might need to know very well the conditions of the soil, whether you want to build a pillar for a new bridge, install a wind turbine or do constructions in a harbor. There are many possibilities.”
Luis Sebastião added that initially the project aimed at using the robots only for the purpose of replacing conventional streamers, for increased flexibility and error reduction, but ended up using other (bigger) robots to carry the sound sources, since a human driving the ship couldn’t follow the desired path with the required accuracy. This permitted a shift, just like Wi-Fi set us free from network cables in our daily lives since the physical freedom is much higher. “By using electric sparks inside the water with an equipment called a sparker, you create a bubble that upon collapsing irradiates sound waves to the bottom. We had two precisely synchronized sparkers firing alternately every second, on two autonomous catamarans, and the underwater robots with the hydrophones followed to do the readings. We managed to decouple from the vessel not only the streamers but also the sound source.” Recently, the fleet of Italian and Portuguese vehicles (7 in total) managed to work in an orchestrated manner during the final survey of the project, in the sea, just outside the port of Sines.
“IST/ISR-Lisboa’s team main task in the project concerned the design and implementation of the cooperative navigation systems for the complete fleet of vehicles. Our team was also very proud to host again the WiMUST trials in Sines, Portugal. We are extremely satisfied with these achievements and look forward to exploring new opportunities in this area.”