According to the United Nations, the world produces about 430 million tons (267 U.S. tons) of plastic annually, two-thirds of which is only used for short periods of time and quickly becomes waste. In addition, plastics are the most harmful and persistent fraction of marine debris, accounting for at least 85% of all marine debris. This problem is easily seen in the Great Pacific Garbage Patch and the amount of plastic waste that washes up on beaches and shores each year. If no action is taken to address this problem, the annual flow of plastic into the ocean could triple by 2040.
One way to address this problem is to improve global tracking of plastic waste using Earth observation satellites. In a recent study, a team of Australian researchers developed a new method for detecting plastic waste on our beaches and successfully tested it on a remote stretch of coast. This satellite imaging tool distinguishes between sand, water and plastics based on the difference in light reflection. It can detect plastics on coastlines from an altitude of more than 600 km (~375 miles) – higher than the orbit of the International Space Station (ISS).
The paper describing their tool, “Beached Plastic Debris Index; “A Modern Index for Detecting Plastic on Beaches,” was recently published by the Marine Pollution Bulletin. The research team was led by Jenna Guffogg, a researcher at the Royal Melbourne Institute of Technology University (RMIT) and the Faculty of Geoinformation Science and Earth Observation (ITC) at the University of Twente. She was joined by several colleagues from both institutions. The study was part of Dr. Guffogg's joint doctoral research supported by an Australian Government Research Training Program (RTP) fellowship.
Dr. Jenna Guffogg said plastic on beaches, as well as in open waters, can have serious impacts on wildlife and their habitats. Photo credit: BPDI
Current estimates suggest that humans dump well over 10 million tons (11 million US tons) of plastic waste into our oceans each year. As plastic production continues to increase worldwide, these numbers are expected to rise dramatically. What ends up on our beaches, just like in open waters, can have serious impacts on wildlife and marine habitats. If these plastics are not removed, they will inevitably break down into micro- and nanoplastics, another major threat to the environment. Dr. Guffogg said in a recent press release from RMIT University:
“Plastics can be confused with food; Larger animals get tangled and smaller ones, like hermit crabs, get caught in things like plastic containers. Remote island beaches have some of the highest plastic densities ever recorded in the world, and we are also seeing increasing amounts of plastic and abandoned fishing gear on the remote coasts of northern Australia.
“While the impacts of these marine plastics on the environment, fisheries and tourism have been well documented, methods of measuring the precise extent of the problem or targeting cleanup efforts, sometimes most needed in remote locations, have been hampered by technological limitations. “
Satellite technology is already being used to track the plastic waste floating in the world's oceans. These include relatively small drifts containing thousands of plastic bottles, bags and fishing nets, but also huge floating garbage islands such as the Great Pacific Garbage Patch. In 2018, this garbage patch was approximately 1.6 million km2 (620,000 mi2) in size and consisted of 45,000–129,000 tonnes (50,000–142,000 US tons). However, the technology used to locate plastic debris in the ocean is largely ineffective in detecting plastic on beaches.
Geospatial scientists have found a way to detect plastic waste on remote beaches, bringing us closer to global monitoring capabilities. Photo credit: RMIT
A big part of the problem is that plastic can be mistaken for specks of sand when viewed from space. The one from Dr. Guffogg and her colleagues' Beached Plastic Debris Index (BPDI) gets around this by using a spectral index – a mathematical formula that analyzes patterns of reflected light. The BPDI is specifically designed to map plastic waste in coastal areas using high-resolution data from the WorldView-3 satellite, a commercial Earth observation satellite (owned by Maxar Technologies) that has been in operation since 2014.
Thanks to their efforts, scientists now have an effective way to monitor plastic on beaches, which could help with cleanup efforts. As part of the remote sensing team at RMIT, Drs. Guffogg and her colleagues developed similar instruments to monitor forests and map bushfires from space. To validate the BPDI, the team tested it in the field by placing 14 plastic targets on a beach in south Gippsland, about 200 km (125 miles) southeast of Melbourne. Each target was made of a different type of plastic and was two square meters in size – smaller than the satellite's pixel size of about three square meters.
The resulting images were compared to three other indices, two for detecting plastics on land and one for detecting plastics in aquatic environments. The BPDI outperformed all three as the others had difficulty distinguishing between plastics and sand or misclassified shadows and water as plastic. As study author Dr. Mariela Soto-Berelov explained, this makes the BPDI far more useful for environments where water and plastic-contaminated pixels are likely to coexist.
“This is incredibly exciting as we have not previously had a tool to detect plastics in coastal environments from space. The beauty of satellite imagery is that it can cover large and remote areas at regular intervals. Detection is an important step in understanding where plastic waste accumulates and in planning cleanups that are consistent with multiple Sustainable Development Goals, such as protecting seas and oceans.”
The next step is to test the BPDI tool in real-world scenarios. To do this, the team will work with various organizations dedicated to monitoring and solving the plastic waste problem.
Further reading: RMIT, Marine Pollution Bulletin
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