Plastic pollution along coastlines is an environmental nightmare. Each year, millions of tons of plastic wash up on beaches worldwide, affecting ecosystems, marine life, and even local economies. But the challenge isn’t just in clearing it up: it’s also in detecting and measuring it reliably. This is where the new study comes in. Using satellite imagery, researchers have developed the Beached Plastic Debris Index (BPDI), which could be a game-changer in tracking beach pollution.

Seeking Plastic from Space

Plastic bottles, packaging, cigarette butts — beach litter comes in different shapes and sizes. It’s also often mixed with sand and vegetation, making it difficult to spot from afar. Traditional beach surveys involve people physically walking the shorelines, a time-consuming and expensive process. But what if you could first map the pollution hotspots, and then concentrate efforts of them?

This is where the new research led by Jenna Guffogg comes in. By harnessing data from satellites like the WorldView-3, the researchers want to create a faster, more accurate picture of where plastics are accumulating. The BPDI, specifically designed for beach settings, leverages the satellite’s shortwave infrared (SWIR) spectral bands, which can capture plastics’ unique “spectral fingerprint.”

It’s not the first time that satellite technology has been used to map plastic. Satellite imagery is already used to track plastic floating in our oceans. However, detecting plastic on a beach is more difficult because it tends to blend in with the surrounding environment.

“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,” said Guffogg, from RMIT University in Australia.

The Science Behind the plastic index

At the core of the BPDI’s effectiveness is the shortwave infrared range. Plastics absorb SWIR radiation differently than natural materials like sand or vegetation, creating a distinct signal in the data. To test the BPDI’s accuracy, researchers conducted an experiment at Shallow Inlet, a sandy coastal area in Victoria, Australia. They placed various plastic targets, including common beach debris like bottle caps and fishing nets, in a grid and then captured satellite images to analyze how well the BPDI could detect the plastic amid the sand.

The researchers didn’t just throw random plastic on the beach. They carefully chose materials based on characteristics like color, transparency, and composition. This allowed them to see how the BPDI performed with different types of plastic.

The study wasn’t limited to testing the BPDI in isolation. The team compared its results against other widely used indices. The BPDI outperformed these indices by a notable margin in separating plastic from other materials like water, sand, and vegetation.

“This is incredibly exciting, as up to now we have not had a tool for detecting plastics in coastal environments from space,” said co-author Mariela Soto-Berelov. “The beauty of satellite imagery is that it can capture large and remote areas at regular intervals. 

We could monitor beach plastic better than ever before

Beyond detection, the BPDI offers two key benefits: speed and scalability. Conducting beach surveys manually isn’t feasible across vast coastlines. Satellite imaging with a precise index like BPDI allows environmental organizations and governments to quickly get an overview of contamination hotspots. This enables them to deploy cleanup resources more effectively, focusing on areas with the highest debris loads rather than using guesswork.

Accuracy is another win for BPDI. Unlike previous indices, which often blurred the line between plastic and organic matter, BPDI consistently showed accurate results even when plastics only covered a small fraction of the image pixels (below 30%). This level of precision is critical for identifying plastic pollution at the early stages, ideally before it spreads further or becomes deeply embedded in the shoreline.

The BPDI’s potential goes beyond just beach monitoring. With modifications, it could be used to monitor riverbanks and estuaries where plastics frequently accumulate before entering oceans.

Moving into the real world

Researchers are now looking to take this index from the test site and into the real world. However, there are still big challenges, and one issue is cost. High-resolution imagery from satellites like WorldView-3 isn’t cheap, which could limit BPDI’s accessibility for low-budget environmental projects or small organizations.

Moreover, environmental factors like cloud cover or moisture in sand could affect BPDI’s performance. The research team found that water absorption of certain wavelengths in the SWIR spectrum could sometimes interfere with the signal, particularly when plastics are partially submerged.

Nonetheless, the research lays a foundation to build on. The index can be refined for different types of weather or terrain conditions, adapted based on the situation. Ridding our beaches of plastic won’t be easy, but at least we can start mapping it.

“We’re looking to partner with organisations on the next step of this research; this is a chance to help us protect delicate beaches from plastic waste,” Soto-Berolov said.

This study lays the groundwork for smarter, more targeted beach cleanups. With further development and wider adoption, tools like the BPDI could transform our ability to manage plastic pollution, helping protect coastal ecosystems and communities alike.

Journal Reference: ‘Beached Plastic Debris Index; A modern index for detecting plastics on beaches’ (DOI: 10.1016/j.marpolbul.2024.117124) by Jenna Guffogg, Mariela Soto-Berelov, Chris Bellman, Simon Jones and Andrew Skidmore is published in Marine Pollution Bulletin.