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A video screen grab shows an illustration of the Cyclone Global Navigation Satellite System.
A video screen grab shows an illustration of the Cyclone Global Navigation Satellite System. (YouTube)

Among the NASA satellites swirling around Earth are eight small ones that measure wind speeds and hurricanes.

Turns out they can do another task: help scientists figure out where microplastics go in the ocean.

Launched in 2016, NASA's Cyclone Global Navigation Satellite System (CYGNSS) measures wind speeds over oceans using radar. The constellation of satellites takes stock of ocean surface roughness - rougher waters mean higher winds.

But the University of Michigan researchers who helped develop the system wondered whether their measurements could help them spot microplastics, too.

Most plastics floating in the ocean break up into what are known as microplastics - plastic particles less than 5 millimeters in diameter. Smaller than a sesame seed, these fragments make their way into animals' stomachs and even our water.

Since microplastics are so tiny, they're difficult to spot. Researchers have long relied on reports from trawlers that snag small bits of plastic along with plankton for a sense of where microplastics go once they enter the water. But that data is incomplete and doesn't reflect real-time conditions.

The researchers used the satellite data to search for areas where the ocean seemed smoother than it should while it was buffeted by high winds. When they compared those areas with observations from plankton trawlers and added in prediction data about where microplastics go given ocean currents, they found a direct connection between surface smoothness and the presence of microplastics.

The new technique revealed that microplastic concentrations peak in each hemisphere during its respective summer season. It also provided even more evidence that China's Yangtze River - long suspected to be a big source of microplastics - spews them into the oceans.

"It's one thing to suspect a source of microplastic pollution, but quite another to see it happening," said Christopher S. Ruf, a climate and space science professor at the University of Michigan who is CYGNSS's principal investigator, in a news release.

He worked on the new method alongside undergraduate Madeline C. Evans. The duo published a paper on their technique in IEEE Transactions on Geoscience in Remote Sensing.

They said they hope the new model helps with cleanup efforts, and attempts to spot pollution at its source.

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