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Emptying into the Arctic Ocean, the 2,800-mile-long Lena River in Siberia forms one of the world’s largest deltas. (USGS)

Earth’s Mirror

Landsat shows us the home planet, warts and all.

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From volcanoes to urban sprawl, crop yields to glaciers, Landsat images have for 40 years told the story of a changing planet. Like the satellites that preceded it, Landsat 8, which was launched in February, carries sensors that detect and measure radiation in seven visible and infrared spectral bands as well as an instrument to measure thermal radiation. It will continue the mission of its predecessors: to give scientists a running account of the surface conditions of Earth.

From This Story

The Landsats have also reached beyond science. They are, says Matt Hansen, a land change scientist and geography professor at the University of Maryland, “a follow-on to those first photos taken by Apollo astronauts.” The environmental idea awakened by seeing the blue Earth hanging in a black void—“Our planet is fragile; we should protect it”—has been intensified by a gallery of Landsat images showing the planet’s diversity and splendor. Says Hansen: “Scientists using Landsat data say ‘It’s absolutely not art. We’re very quantitative. We’re not cooking here.’ ” But Hansen believes that geography is also qualitative. Moreover, the U.S. Geological Survey, which manages the Landsat data archive in Sioux Falls, South Dakota, maintains on its Web site a gallery, “Earth as Art” (eros.usgs.gov/imagegallery). And NASA, responsible for building the satellite and its sensors and launching them, has published an eBook with the same title. Among the book’s 95 images is a picture of Russia’s Lena River Basin, which shows what can be done with the spectral bands of Landsat 7’s sensors. Compare the pretty pictures in these collections, Photoshopped as they are, to the ruddy sameness of pictures sent back from Mars; you may come away with the happy conviction that there’s no place like home.

But the story of change told by the series of seven Landsats is a story of human impact, and that is not a pretty picture. In the 40 years since the first satellite was launched, the number of humans on Earth has almost doubled, from under four billion in 1972 to more than seven billion in 2013. The record preserved in the Landsat archive is the record of loss—of forests, glaciers, and pristine, natural spaces—as humans occupy ever more area on Earth and affect its climate. “We are an impressive species,” says Hansen. “We are everywhere doing stuff. And very few forests are left alone. From Scandinavia to Australia to Chile, Brazil, and back up to Canada—the forests are just used all the time.”

There’s an up side to the story, though, and Landsat is also essential to it. Impressive for their reach and appetites, humans are equally impressive for analyzing and understanding change. Landsat images have been used around the world by resource managers who have put in place practices to mitigate human impact as well as cope with the effects of natural forces like floods and wildfires.

An even sunnier side of the story: Since 2008, Landsat archived imagery has been free and accessible without restriction to anyone in the world. As of August 2012, nine million images have been downloaded.

Change

Tom Loveland, the USGS lead of the interagency Landsat science team, has spent a career studying land cover change. Among the most dramatic changes he’s seen are in a pair of images of Beijing.

“We’ve been imaging Beijing and the rest of the planet since 1972, so because we’re looking at it periodically over time, we have this continuous record that allows us to go back after an event and see what was then and how it has changed as a result of the event,” he says.

Loveland points out that the image of Beijing in the mid-1970s shows a compact urban center. Surfaces like roads and rooftops appear blue or gray, surrounded by the green of vegetation. In a 1990s image, the blues and grays have sprawled outward; three concentric circles are visible, the outer beltways of Beijing. Says Loveland: Once the economic engagement with the West began, with the 1972 visit to China by U.S. President Richard Nixon, the satellites began to see the city’s massive growth.

Landsat has recorded surface change not only on the most populated continent, but also on the least populated. In Antarctica, there is simply no way other than satellite remote sensing to keep track of what’s going on, says glaciologist and NASA scientist emeritus Robert Bindschadler. “Satellites can guide field researchers to the places where things are happening,” he says. “Without them, we’d just be flailing in a dark room.” Data from Landsat and other satellites, for example, indicated that the Pine Island Glacier on the continent’s west coast was thinning and accelerating seaward. “We could see that the trigger was at the coast,” says Bindschadler, “and that led to the NASA IceBridge flights,” which made headlines in 2011 with the discovery of a 19-mile-long crack in the glacier, which has by now extended several more miles.

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