Antarctica may appear to be a land frozen in time, but it certainly is not still. Glaciers plow down the continent's center to the sea, icebergs snap off and crash into the ocean, and great rivers of ice snake through the ice sheet, evidence of a dynamic relationship between this remote continent and global climate.

A joint NASA and Canadian Space Agency mission now provides a more comprehensive view of how the Antarctic ice sheet moves and changes and may help answer some fundamental questions about this mysterious place at the end of the world, including whether the ice sheet is advancing or retreating.

The initial mapping campaign, the 1997 Antarctic Mapping Mission, resulted in the first high-resolution radar satellite map of the continent. The second phase, the Modified Antarctic Mapping Mission, completed last November, once again charted Antarctica with space-based imaging radar. This second mission gives scientists a way to see how the continent has changed over the past three years as well as a wealth of new information on the movement of the most active region, the outer half of the ice sheet.

"The 1997 map became a benchmark for studying changes on the continent and also revealed fascinating features, including enormous ice streams in East Antarctica, that we had never seen before. We expect to find even more surprises from this second, even more detailed map that will help us unravel some of the mysteries behind how our global environment behaves," said Dr. Ghassem Asrar, Associate Administrator for NASA's Office of Earth Sciences, Washington, D.C.

For the new mission, the Canadian Space Agency's RADARSAT-1 satellite trained its imaging radar on the outer half of the continent twice during each of three consecutive 24-day periods, ending last Nov. 14. "The mission was a challenge for us because we had to accurately navigate the satellite to within a few hundred meters of its nominal track on each orbit," said Rolf Mamen, Director General of Space Operations at the Canadian Space Agency.

Precise navigation and data from the six passes make it possible to create detailed topographic maps and to measure the speed of the moving glaciers. "Most of the Antarctic ice sheet moves imperceptibly slowly but nevertheless surely," says science team member Dr. Frank Carsey of NASA's Jet Propulsion Laboratory, Pasadena, Calif.

"This mission gives us an overall snapshot of how the ice moves and how it is changing. By measuring the extent and velocity of the moving ice and estimating its thickness, we can estimate how much ice may be lost into the ocean from Earth's largest storehouse of freshwater," Carsey added. "These calculations are important for understanding Antarctica's contribution to the present rate of sea-level rise of about two millimeters, or the thickness of a dime, a year."

Mission scientists are now developing velocity maps showing the direction and speed of the ice. They have already created the first-ever complete velocity maps of the spectacular Lambert Glacier, a sinuous ice stream more than 500 kilometers (311 miles) long, which reaches speeds of more than one kilometer (about two-thirds mile) a year once the ice spreads onto the Amery Ice Shelf.

They are also beginning to create a new map of Antarctica to compare with the one made in 1997. The process of turning the radar images into map-quality mosaics will take about a year to complete.

"We already can see several glaciers along the Antarctic Peninsula coastline where the ice edge has retreated over 30 kilometers (about 19 miles) in just three years. But this is not the whole story. We also see places where the ice sheet is advancing, such as the Amery Ice Shelf. The Antarctic Ice Sheet is huge, and this is the first time we have the data to study and compare ice sheet behavior around the entire continent," says mission principal investigator Dr. Kenneth Jezek, of Ohio State University's Byrd Polar Research Center. "These data will help us determine whether the local changes we see represent expected, episodic behavior or whether they represent regional trends driven by changing climate. "

More information on the mission is available on the Internet at . Images associated with this release are available at .

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