NASA’s Ice, Cloud and land Elevation Satellite (ICESat)
has resumed measurements of the Earth’s polar ice sheets,
clouds, mountains and forests with the second of its three
lasers. Crisscrossing the globe at nearly 17,000 miles per
hour, this new space mission is providing data with
unprecedented accuracy on the critical third dimension of the
Earth, its vertical characteristics.

“The first set of laser measurements is revealing features of
the polar ice sheets with details never seen before, and is
detecting dust storms, cloud heights, tree heights and smoke
from forest fires in new and exciting ways,” said Jay Zwally,
ICESat Project Scientist at NASA’s Goddard Space Flight
Center, Greenbelt, Md.

The principal mission of ICESat is to measure the surface
elevation of the large ice sheets covering Antarctica and
Greenland. Measurements of elevation-change over time will
show whether the ice sheets are melting or growing as the
Earth’s climate undergoes natural and human-induced changes.

The Geoscience Laser Altimeter System (GLAS) instrument on
ICESat sends short pulses of green and infrared light though
the sky 40 times a second, all over the globe, and collects
the reflected laser light in a one-meter telescope. The
elevation of the Earth’s surface and the heights of clouds
and aerosols in the atmosphere are calculated from both
precise measurements of the travel time of the laser pulses,
and ancillary measurements of the satellite’s orbit and
instrument orientation. This marks the first time any
satellite has made vertical measurements of the Earth through
the use of an onboard light source.

Operating in a near-polar orbit, ICESat is adding to our
understanding of the mass-balance of the Greenland and
Antarctic ice sheets. ICESat’s first topographic profiles
across Antarctica revealed details of features such as the
ice streams of the Siple Coast and the Amery Ice Shelf, as
well as the atmospheric phenomena above them.

ICESat is also making unique measurements of cloud heights
and global distribution. ICESat detects distributions of
aerosols from sources such as dust storms and forest fires.
And because its laser pulses continuously, ICESat also
measures the Earth’s topography with high accuracy.

“ICESat has already demonstrated the unique capability of
lasers to make a variety of Earth Science measurements. When
the calibration experiments are completed, we believe the
accuracy and sensitivity will exceed previous capabilities by
nearly an order of magnitude,” stated Bob Schutz, GLAS
Science Team Leader, of the University of Texas at Austin.

ICESat was launched January 12, 2003, on a Boeing Delta II
rocket from Vandenberg Air Force Base, Calif. On March 29,
ICESat’s Laser 1 unexpectedly stopped working after providing
36 days of data. NASA will issue a report shortly on the
reason for the anomaly.

“Despite the problem with the first laser, ICESat is
providing a new perspective on elements within the Earth
System with amazing accuracy. We are especially looking
forward to the information this capability will provide on
how the polar ice sheets are changing,” said Waleed Abdalati,
ICESat Program Scientist at NASA Headquarters, Washington.

The ICESat scientists will convene a special session to
present the latest results from ICESat at the 2003 Fall
Meeting of the American Geophysical Union in San Francisco.

ICESat is the latest in a series of NASA’s Earth observation
spacecraft designed to study the environment of our home
planet and how it may be changing. NASA’s Earth Science
Enterprise is dedicated to understanding the Earth as an
integrated system and applying Earth System Science to
improve prediction of climate, weather and natural hazards
using the unique vantage point of space.

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