Discovering the Surface of Greenland

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The technology makes use of existing Earth-observing satellites. But these aren't the only ones up there. Other satellites, notably NASA's Landsat and ASTER sensors, are also well-known for making sharp images of the home planet. The main advantage of Terra and Aqua, though, is the greater sensitivity to subtle light contrasts--a big help when the photographic subject is a vast white surface. Plus, Terra and Aqua are available more often. Landsat doesn't cross the same spot more than once every 16 days. Since many satellite images are unusable because of cloud cover, as a practical matter it would take many hundreds of Landsat images to make a similar map, Scambos says.

The new approach also allows rapid reevaluation of the entire sheet on Greenland to detect important short-term changes. In fact, the technology allows scientists to build a new high-res picture of the entire sheet every two months. And if scientists decide that they'd like another look at a small area, other satellites can potentially be brought to bear.

The subject is of more than academic interest, notes Mark Fahnestock, a geologist at the University of New Hampshire, in Durham, who collaborated with Scambos on the technology. "Basically, the Greenland ice sheet is putting out--in the last six, seven years--40 percent more ice than it was ten years earlier," Fahnestock says. "We are trying to understand why, so we can have some idea of how to project it into the future." Once this understanding becomes clearer, scientists will be able to tell the world how fast and how far sea levels might rise. This might even prod policymakers to reduce greenhouse-gas emissions and plan for receding coastlines and the inundation of populated areas.

One of the disturbing trends in Greenland is the growth of huge lakes of ice melt that form atop the ice sheet during summer months. These masses of water find cracks and drain deep into the ice sheet, to uncertain effect. The new imaging technology can see such cracks and how they are changing, Fahnestock says.

At a high level, the technology can show ice as a kind of slow-motion river. "In a river you can see standing waves and rapids," Fahnestock says. "It's the same sort of picture of the ice, even though it is moving much slower. You see this bumpiness because this ice is in motion." The rate of ice-sheet melting is poorly understood, and "knowing where it's bumpy lets us figure out why Greenland is changing as fast as it is today," he says.