Satellites Can Spy on Microplastics, Researchers Show

In fictional stories told on pages, stages, and screens, it’s not uncommon for lovelorn beachgoers to find romantic messages in bottles. In the reality that is the 21st century, however, there’s only one thing that people are guaranteed to find when they visit the coast: plastic.

Every year, over 8 million metric tons of plastic waste end up in the ocean, where 150 million metric tons of plastic already linger, according to the environmental advocacy group Ocean Conservancy. Encompassing everything from plastic bottles, bags, and straws to plastic food containers, plates, and packaging, the waste impacts nearly 700 marine species that call the oceans home and often mistake plastic for food.

Especially harmful to marine wildlife are microplastics—small bits of plastic that are created when plastic waste is subjected to wind, waves, and sunlight. Because they’re so tiny, microplastics are easy for animals to ingest, difficult to clean up, and extremely mobile. In fact, they’re so lightweight that microplastics often travel hundreds of thousands of miles from their point of entry atop raucous ocean currents.

Although it isn’t easy to do, many organizations want to help remove microplastics from oceans. In order to do so, they must be able to locate microplastics at sea, including where they’re coming from and in what direction they’re going. Fortunately, that’s about to become a lot easier thanks to researchers at the University of Michigan, who announced last month that they have developed a new method for finding and tracking microplastics on a global scale.

Led by Frederick Bartman Collegiate Professor of Climate and Space Science Chris Ruf, the research team is using satellites—specifically, NASA’s Cyclone Global Navigation Satellite System (CYGNSS), a constellation of eight microsatellites developed by the University of Michigan to measure wind speeds over Earth’s oceans, thereby increasing the ability of scientists to understand and predict hurricanes. To determine wind velocity, the satellites use radar images to gauge the roughness of the ocean’s surface. The same data, researchers found, can be used to detect marine debris.

“We’d been taking these radar measurements of surface roughness and using them to measure wind speed, and we knew that the presence of stuff in the water alters its responsiveness to the environment,” said Ruf, who reported his findings in a paper titled “Toward the Detection and Imaging of Ocean Microplastics With a Spaceborne Radar,” published in June by the Institute of Electrical and Electronics Engineers (IEEE). “So I got the idea of doing the whole thing backward, using changes in responsiveness to predict the presence of stuff in the water.”

Surface roughness isn’t caused by microplastics themselves, however. Rather, it’s caused by surfactants, which are oily or soapy compounds that lower the tension on a liquid’s surface and often accompany microplastics in the ocean.

“Areas of high microplastic concentration, like the Great Pacific Garbage Patch, exist because they’re located in convergence zones of ocean currents and eddies. The microplastics get transported by the motion of the water and end up collecting in one place,” Ruf explained. “Surfactants behave in a similar way, and it’s very likely that they’re acting as sort of a tracer for the microplastics.”

Currently, environmentalists tracking microplastics rely mostly on anecdotal reports from plankton trawlers, who often net microplastics along with their catch. Unfortunately, trawlers’ accounts can be incomplete and unreliable. Satellites, on the other hand, are an objective and consistent data source that scientists can use to create a day-by-day timeline of where microplastics enter the ocean, how they move across it, and where they tend to collect in the water. For example, Ruf and his team have determined that microplastic concentrations tend to be seasonal; they peak in June and July in the Northern Hemisphere, and in January and February in the Southern Hemisphere.

Researchers also confirmed that a major source of microplastics is the mouth of China’s Yangtze River, which has long been suspected to be a microplastics culprit. 

“It’s one thing to suspect a source of microplastic pollution, but quite another to see it happening,” Ruf said. “What makes the plumes from major river mouths noteworthy is that they are a source into the ocean, as opposed to places where the microplastics tend to accumulate.”

Ruf, who developed his tracking method alongside University of Michigan undergraduate Madeline C. Evans, says environmental cleanup organizations can use high-fidelity microplastics intelligence to deploy ships and other resources more effectively. One such organization, for example, is Dutch nonprofit The Ocean Cleanup, which is working with Ruf to confirm and validate his initial findings. Another is the United Nations Educational, Scientific, and Cultural Organization (UNESCO), which is currently seeking new ways to track the release of microplastics into marine environments.

“We’re still early in the research process, but I hope this can be part of a fundamental change in how we track and manage microplastic pollution," Ruf concluded.