Tracking marine litter in the Arctic from the air
On the current Polarstern expedition, scientists from the Alfred Wegener Institute have deployed a multicopter with a high-resolution camera to quantify marine litter floating on the sea surface. The deep-sea researchers had recorded a marked increase of man-made litter on the Arctic seafloor over the last ten years. That was the reason to now start the programme for the quantitative analysis of waste-entry on the sea surface.
The quantitative studies of litter in the Arctic are the prelude to the so-called Pollution Observatory, a component of the FRAM Infrastructure (Frontiers in Arctic Marine Monitoring), which is funded by the Helmholtz Association. The idea came from Dr Melanie Bergmann, Deep-Sea Ecologist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). For a number of years, her research has focused on the subject of marine litter, and, she has found that in certain areas of the deep Arctic Ocean, there is as much litter on the seafloor as there is near the city of Lisbon. Overall, the pollution is steadily increasing: "In some areas, there has been a twenty-fold increase in litter over the past decade," says Melanie Bergmann.
The AWI biologist also discovered floating plastic litter on the sea surface, and much more has been identified during the on-going expedition than in the study from 2012 with a helicopter. Depending on sea state and light conditions, observations from the ship's rail can be difficult because of the angle of view. An alternative method to assess litter involves manned helicopter flights, but these are also very expensive and only large object can be seen from great heights. Fortunately, scientists and engineers in the HGF-MPG Joint Research Group for Deep-Sea Ecology and Technology are working very closely together. To assess marine litter at the sea surface, they developed a multicopter, which can be used when the ship is committed to stationary work.
"During a Polarstern expedition in the Arctic in 2015, we already used a multicopter, which we developed together with colleagues from the University of Würzburg," explains Sascha Lehmenhecker, Lead Engineer for this new technology of the Deep-Sea Research Group of the AWI. The new multicopter with its 24-megapixel compact camera weighs 4.8 kg. "With this weight and a size of 50 by 50 centimetres, it is possible to fly for 20 minutes and, in the view of the pilot, to cover a distance of up to six kilometres," says Lehmenhecker.
Another important step of the development, which took place in the Helmholtz Alliance Robotic Exploration of Extreme Environments (ROBEX), was to use a multicopter safely despite magnetic aberration at the North Pole and various confounding factors caused by the ship. "This was only possible after we no longer used the magnetic compass for navigation," Lehmenhecker explains. The task of determining the location of its own axis is now taken over by two mounted GPS receivers, a fast computer and a complex, specifically programmed software.
The newly developed sensor electronics of the multicopter also calculate when and how often a photo should be taken. "The use of such a multicopter can help us to grasp the extent and distribution of plastic litter that is floating at the sea surface," Melanie Bergmann explains. She uses the images from the multicopter flights, to detect floating litter and other large objects in well-defined areas on the sea surface. "Eighty-eight percent of fulmars from Spitsbergen already have waste in their stomachs. This is another indication that the 6th Rubbish Patch, as projected by oceanographers from the Imperial College London, is in the process of becoming a reality in the north, in addition to the five known garbage patches in temperate latitudes," says Bergmann. "Our new technology allows us to track such developments with little technical effort in order to increase the awareness of this environmental problem," says the scientist.