Multiple cleanup and prevention initiatives target the ghost gear issues around the globe, with the Global Ghost Gear Initiative (GGGI) being the largest international alliance of over 100 entities, founded in 2015. The organization brings together various stakeholders, including industry, academia, governments, and NGOs, to address the environmental and economic impacts of ghost gear in the world’s oceans.
Side-Scan Sonar Detection
One of the founding members of the Global Ghost Gear Initiative is the World Wide Fund for Nature (WWF). WWF has been actively involved in tackling the widespread problem of ghost nets through both global and localized projects.
A notable WWF initiative in Europe is the GhostDiver App, introduced in 2020. The app lists the suspected locations of ghost nets obtained with side-scan sonar surveys and encourages experienced divers to visit and confirm these locations, as well as report newly discovered ghost gear. Diver-verified ghost gear can be subsequently removed by professional team efforts and retrieved ghost gear are recorded to support mitigation measures.
WWF Germany has been successfully implementing side-scan sonar technology to search for ghost nets since 2018. Back then, the organization liaised with sonar imaging experts from the US to benefit from the technology in the Baltic Sea, known for its low-visibility waters.
Ghost net surveys conducted by WWF Germany involve towing a side- scan sonar in the survey area and analyzing the sonar visuals for cues. The operator must be trained and have enough experience to recognize a potential ghost net in the side-scan sonar images at various angles, a time-consuming process that might require several runs over the object. Another limitation of towed technology is entanglement of the sonar in the ghost net itself, and the efforts needed for deployment and recovery.
Automating the Search
Modern autonomous uncrewed surface vehicles (USVs) can open up new opportunities for improving and automating the search for ghost nets, and in April 2024, WWF Germany met with experts from EvoLogics for a demonstration session of the Sonobot 5 vehicle, a small catamaran platform with a side-scan sonar and AI-powered object recognition.
The goal was to demonstrate the workflow of conducting a side-scan survey with the Sonobot and to verify that ghost nets are visible in its sonar output.
Taking place near the town of Kiel-Schilksee, the Sonobot trials involved placing sample nets at 5- and 10-meter depths at known locations in the Kieler Förde, an inlet of the Baltic Sea. The vehicle then ran a sonar survey over a pre-programmed grid at the location. For the experiments, the net was laid out straight, along a curved line, and randomly folded to imitate the real-world occurrence of ghost gear. The net was successfully identified in the Sonobot’s sonar imagery.
A net (a straight line) is visible in the Quadroin side-scan sonar output on the left. (Image credit: EvoLogics)
The positive outcome is promising to further advance the search for ghost nets with EvoLogics object recognition, an AI-based system that runs directly onboard the vehicle and analyzes raw side-scan sonar output. Found objects are detected and highlighted in the operator’s control software in real time.
With enough sample data, EvoLogics’ object recognition neural network can be trained to detect nets. This allows the search for ghost gear to be conducted with robotic technology that helps scale up and simplify these missions.
Future Prospects
In 2023, EvoLogics trialed a cooperative mission of the Sonobot vehicle with a team of divers working with the company’s newly released Diver Navigation system. The system enables georeferenced underwater map-based navigation and text message exchange between the divers and with the support team on the surface.
Location of an object identified by the Sonobot’s object recognition system was sent to the maps on the diver consoles, so the team could navigate towards it for visual inspection and confirmation. The same setup could benefit the ghost gear cleanup operations, where the Sonobot would survey the area, detect an object, and direct a team of professional divers towards it for recovery.
The Sonobot platform is suitable for inland and harbor waters, and for the open sea, EvoLogics experts see a lot of potential for its Quadroin autonomous underwater vehicle (AUV). Carrying a side-scan sonar, a downward-facing underwater camera, and an object recognition module, the Quadroin AUV could detect ghost gear away from the coastlines.
During the Quadroin’s trials in the Attersee (Austria) in June 2024, the team encountered a fishing net and verified that it was visible in both the Quadroin’s side-scan and video feeds. Thus, the AUV is a viable side- scan sonar carrier for ghost net surveys.
Autonomous AI-powered side-scan sonar surveys can improve the cost and time efficiency for ghost net cleanup, and EvoLogics is looking forward to future workshops to drive the technology forward.
To find out more, visit: www.evologics.com www.wwf.de/themen-projekte/plastik/geisternetze
This feature appeared in Environment, Coastal & Offshore (ECO) Magazine’s 2024 Autumn edition Sampling & Survey, to read more access the magazine here.
