Maps of Antarctica are nearly all white--but not because of the snow and ice. Rather, this frozen land contains the largest unmapped regions on earth. Teams of scientists regularly make the four-hour jaunt from the main U.S. base at McMurdo Sound to the permanent South Pole station. But even today, parties on the ground are little better off than the great explorers--Robert Falcon Scott, Roald Amundsen and Ernest Shackleton--were, as they struggle to find their way across an uncharted continent the size of the U.S. and Mexico combined.

That is about to change: the last terra incognita is being mapped. From September 26 to October 14, RADARSAT, an earth-sensing satellite operated by the Canadian Space Agency (CSA), pointed its instruments at Antarctica as it made hundreds of passes over the South Pole from various angles.

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Cartographers at the Byrd Polar Research Center at the Ohio State University will "stitch" the collection of more than 8,000 images together to produce the most detailed map ever made of Antarctica--a process that will take more than a year to complete. "The last satellite map of Antarctica not only failed to provide an entire picture but required images from 13 different satellites over a six - year period from 1980 to 1987," says Rolf Mamen, director general of space operations at the CSA.

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NASA launched RADARSAT for Canada in 1995, in return for two mapping missions over Antarctica during the satellite's lifetime. The Antarctic Mapping Mission is part of NASA's Mission to Planet Earth program. RADARSAT's microwave radar system can pierce cloud cover, smog, haze, smoke and darkness. It can be programmed to capture images of an area as wide as 320 miles (500 kilometers) and can detect objects as small as 26 feet (eight meters) long.

The new composite snapshot of the Antarctic was made possible by rotating the RADARSAT satellite 180 degrees from its normal orientation and by making use of its ability to aim its radar beam so it would cross the pole in each pass. The rotation took place on September 11; the satellite was returned to its standard configuration on November 4.

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From the very first, the pictures snapped by RADARSAT excited polar scientists. An early image of the Amunsden-Scott Station at the South Pole revealed traces of a long - abandoned runway and picked up radar reflections that are probably buildings from the first polar station, established by Admiral Richard E. Byrd in 1957. These buildings are now buried under more than 30 feet (9 meters) of snow and ice.

The South Pole station sits at the center of a vast plain of ice, ringed in by mountain ranges. The elevation there is 9,000 feet (2,700 meters) above sea level--and it is ice all the way to the bottom. From here the ice flows to the sea. This enormous reservoir contains 70 percent of the Earth's fresh water. Changes in this ice directly influence world sea levels and climate; were all of it to melt, global sea levels would rise by 230 feet (70 meters).

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The strikingly beautiful high-resolution images from RADARSAT reveal features of "the Ice" with startling clarity. They show ice streams, rivers of ice measuring tens of miles wide and about half a mile thick that flow rapidly within the predominantly slow-moving ice sheet. These streams feed the "ice shelves," large, floating slabs of ice that form most of the Antarctic coastline. The ice moves seaward at about half a mile per year, occasionally "calving" to form huge icebergs. When the creeping ice grinds against the seabed or crosses an obstruction on land, progress is slowed and the ice bulges upward, forming ice rises.

The new data are already helping scientists to better understand the formation and flow of the Antarctic ice. "The radar image of earth's geographic South Pole shows an unexpectedly complex surface structure over what was previously believed to be the nearly featureless East Antarctic Ice Sheet," says Kenneth Jezek, director of the Byrd Polar Research Center. He believes the textured features mirror the bedrock topography beneath the ice sheet.

The critical question is whether the ice sheets are expanding or shrinking. If a warming ocean melted the ice sheets from beneath, the rate of flow from the continent would increase--potentially leading to a catastrophic rise in sea level. The images promise to provide some answers. And already scientists are looking forward to the next RADARSAT mapping in several years. Comparing those images to this earlier set will allow them to see any changes that have occurred.