Plastic Waste on our Beaches Now Visible from Space, Says New Study

According to the United Nations, the world produces about 430 million metric tons (267 U.S. tons) of plastic annually, two-thirds of which are only used for a short time and quickly become garbage. What’s more, plastics are the most harmful and persistent fraction of marine litter, accounting for at least 85% of total marine waste. This problem is easily recognizable due to the Great Pacific Garbage Patch and the amount of plastic waste that washes up on beaches and shores every year. Unless measures are 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 the global tracking of plastic waste using Earth observation satellites. In a recent study, a team of Australian researchers developed a new method for spotting plastic rubbish on our beaches, which they successfully field-tested on a remote stretch of coastline. This satellite imagery tool distinguishes between sand, water, and plastics based on how they reflect light differently. It can detect plastics on shorelines from an altitude of more than 600 km (~375 mi) – higher than the International Space Station‘s (ISS) orbit.

The paper that describes their tool, “Beached Plastic Debris Index; a modern index for detecting plastics 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 Geo-Information Science and Earth Observation (ITC) at the University of Twente. She was joined by multiple colleagues from both institutions. The study was part of Dr. Guffogg’s joint PhD research with the support of an Australian Government Research Training Program (RTP) scholarship.

According to current estimates, humans dump well over 10 million metric tons (11 million U.S. tons) of plastic waste into our oceans annually. Since plastic production continues to increase worldwide, these numbers are projected to increase dramatically. What ends up on our beaches can severely impact wildlife and marine habitats, just like the impact it has in open waters. If these plastics are not removed, they will inevitably fragment into micro and nano plastics, another major environmental hazard. Said Dr. Guffogg in a recent RMIT University press release:

“Plastics can be mistaken for food; larger animals become entangled, and smaller ones, like hermit crabs, become trapped inside items such as plastic containers. Remote island beaches have some of the highest recorded densities of plastics in the world, and we’re also seeing increasing volumes of plastics and derelict fishing gear on the remote shorelines of northern Australia.

“While the impacts of these ocean plastics on the environment, fishing and, tourism are well documented, methods for measuring the exact scale of the issue or targeting clean-up operations, sometimes most needed in remote locations, have been held back by technological limitations.”

Satellite technology is already used to track plastic garbage floating around the world’s oceans. This includes relatively small drifts containing thousands of plastic bottles, bags, and fishing nets, but also gigantic floating trash islands like the Great Pacific Garbage Patch. As of 2018, this garbage patch measured about 1.6 million km² (620,000 mi²) and consisted of 45,000–129,000 metric tons (50,000–142,000 U.S. tons). However, the technology used to locate plastic waste in the ocean is largely ineffective at spotting plastic on beaches.

Much of the problem is that plastic can be mistaken for patches of sand when viewed from space. The Beached Plastic Debris Index (BPDI) developed by Dr. Guffogg and her colleagues circumvents this by employing a spectral index – a mathematical formula that analyzes patterns of reflected light. The BPDI is specially designed to map plastic debris in coastal areas using high-definition 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 assist in clean-up operations. As part of the remote sensing team at RMIT, Dr. Guffogg and her colleagues have developed similar tools for monitoring forests and mapping bushfires from space. To validate the BPDI, the team field-tested it by placing 14 plastic targets on a beach in southern Gippsland, about 200 km (125 mi) southeast of Melbourne. Each target was made of a different type of plastic and measured two square meters (21.5 square feet) – smaller than the satellite’s pixel size of about three square meters.

The resulting images were compared to three other indices, two designed for detecting plastics on land and one for detecting plastics in aquatic settings. The BPDI outperformed all three as the others struggled to differentiate 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 up to now we have not had a tool for detecting plastics in coastal environments from space. The beauty of satellite imagery is that it can capture large and remote areas at regular intervals. Detection is a key step needed for understanding where plastic debris is accumulating and planning clean-up operations, which aligns with several Sustainable Development Goals, such as Protecting Seas and Oceans.”  

The next step is to test the BPDI tool in real-life scenarios, which will consist of the team partnering with various organizations dedicated to monitoring and addressing the plastic waste problem.

Further Reading: RMIT, Marine Pollution Bulletin

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