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 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.
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
Sky Image at Bonneville
The series of near-circular green spots in the sky picture are caused by the
green-laser pulses from GLAS illuminating thin clouds or aerosols in the atmosphere.
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
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.
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 the first polar-orbiting satellite to directly measure the heights
of clouds and aerosols.
"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.
More information, movies and high resolution images see: NASA Goddard Space Flight Center