Mar. 26, 2001 There appears to be a new crack in the Antarctic's icy armor. The massive iceberg-to-be was captured by a NASA satellite that's also tracing hidden continental features that shape the future of the world's largest ice sheets.
Landsat 7, a cooperative mission between NASA and the United States Geological Survey, Reston, VA, completed its second annual continent-wide mapping of Antarctica last month. With its capability to see features as small as 15 meters (50 feet) across, Landsat 7 provides the most detailed observations available of the remote continent, many parts of which have never been mapped at this resolution before.
"This multi-year archive of Landsat 7 images is an invaluable investment in research on Antarctica," says glaciologist Robert Bindschadler of NASA's Goddard Space Flight Center, Greenbelt, MD, a member of the Landsat 7 science team. "We only have one chance to capture today's changes on this dynamic continent, and with this targeted mapping strategy, we're committed to doing that." NASA plans to conduct annual Antarctic surveys.
On January 16 Bindschadler, during his daily review of new Landsat 7 images of Antarctica, noticed a striking feature on the Pine Island Glacier: a thin crack more than 25 kilometers (15 miles) long, stretching more than two-thirds of the way across the glacier. There was no crack in a previous image 10 months earlier.
To get a fix on when the fracture had formed and how fast it was growing, Bindschadler contacted colleagues working with other earth-observing sensors -- two instruments onboard NASA's Terra satellite, the Canadian Space Agency's Radarsat, and the European Space Agency's radar imager. By comparing observations from different dates, the researchers were able to estimate the growth rate of the crack and when it had formed.
"Most of this crack formed very rapidly, in less than five weeks," says Bindschadler. "Right now it is growing much more slowly, at about 13 meters (40 feet) a day. My prediction is that the crack will result in the calving of a major iceberg in probably less than 18 months."
Landsat 7 was launched by NASA in April 1999 and began routine scientific observations in June 1999. Images are archived, processed, and distributed by the U.S. Geological Survey, which is also responsible for day-to-day operations of the satellite.
Landsat 7 passes over the continent 16 times a day in its nearly pole-to-pole orbit, taking an average of 300 images each week during the Antarctic summer (November to February) when the surface is best illuminated with sunlight.
This year's collection of images promises to reveal a wealth of new surface features due to a change in the spacecraft's observing schedule. In previous years, Landsat took images of the surface as it approached the pole, but this year for the first time images were taken after the spacecraft passed by the pole. The new viewing angle changed the patterns of shadows on the uniform, white surface, exposing subtle differences in surface topography.
When the two years of Antarctic images taken at different sunlit angles are combined, researchers will not only have an unprecedented view of the ice surface, they will also be able to infer the hidden topography of the continental bed below. Features visible on the ice are shaped by the contours and roughness of the underlying surface as the ice slowly moves across it.
This Landsat 7 project is part of NASA's Earth Science Enterprise, an interdisciplinary research program dedicated to improving our understanding of the Earth System and how it is changing due to both natural and human-induced processes.
Images to illustrate this story are available on the Internet at: http://www.gsfc.nasa.gov/gsfc/earth/environ/antarctic/pineisla nd.htm
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