David E. Steitz
Headquarters, Washington, DC            February 21, 2001
(Phone:  202/358-1730)

Rosemary Sullivant
Jet Propulsion Laboratory, Pasadena, CA
(Phone:  818/354-0474)

RELEASE:  01-24

SPACE MAPPING MISSION CATCHES ANTARCTICA IN MOTION

     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, DC.

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, CA. 

"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 (18.6 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:
        http://www-bprc.mps.ohio-state.edu/radarsat
Images associated with this release are available at:
       http://www.jpl.nasa.gov/pictures/antarctica

                           -end-