Environmental watchdogs now can detect deforestation even when it's hidden from sight by rain and clouds. They're using data from radar on a European satellite.



The world continues to lose some of its most valuable tropical forests, millions of acres each year. Defenders of the forest are trying to halt that and preserve endangered species and slow down climate change. They just deployed a new tool in that effort. Here's NPR's Dan Charles.

DAN CHARLES, BYLINE: Practically every day, Mikaela Weisse transports herself by computer to distant tropical forests.

MIKAELA WEISSE: OK. So we're in the Central African Republic. That's where I'm zooming in.

CHARLES: She's sharing her computer screen. We see a map of the forest created from a flood of images collected by satellites. Weisse works for the World Resources Institute, and she helps run this site called Global Forest Watch. Behind the scenes, computers sift through the images as they come in day by day. And when the software detects a change, when trees have disappeared, it issues an alert.

WEISSE: If we can detect deforestation and other changes as soon as they're happening, then there's a possibility to send in law enforcement or what have you to actually stop it before it goes further.

CHARLES: There's some evidence that this works, she says. According to one study, in places where people know they're being watched, there's been less forest clearing. One problem, though - when it's raining or cloudy, regular satellite sensors can't see the forest. And it rains a lot in the tropics.

WEISSE: In Indonesia, my impression is it's the rainy season almost all the time (laughter). So there's, like - there's almost always cloud cover.

CHARLES: So it might not be possible to see deforestation until months later when the weather clears. But last month, Weisse and her colleagues unveiled something new. Their system now collects images from an additional kind of satellite sensor, radar, which sees right through clouds.

WEISSE: Essentially, the satellites are, like, sending radio waves to the Earth and collecting how they come back.

CHARLES: The satellite's operated by the European Space Agency. And it delivers even sharper pictures than what Global Forest Watch had been getting.

WEISSE: And so we can actually see these little patches that indicate where there's been, you know, removal of a single tree.

CHARLES: At that site in Central African Republic in front of us on the computer, the map shows dark pink spots where trees disappeared just within the past few weeks. Anybody in the world can log in and see this. So local environmentalists or even big food companies that have pledged not to buy crops grown on deforested land can react more quickly.

Dan Charles, NPR News.

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