More clues in the global warming
mystery and its resulting polar ice cap melts will emerge from NASA’s
next space mission, thanks to the leadership of engineers at The
University of Texas at Austin who helped design the mission’s
instruments and will monitor their valuable measurements.
Dr. Bob Schutz, professor of aerospace engineering
and engineering mechanics and associate director of the Center
for Space Research, is the science/engineering team leader
for NASA's ICESat mission.
Powerful laser-based instrumentation designed to precisely measure
Earth’s features that influence sea levels will launch Dec.
19 aboard NASA’s new Ice, Cloud and Land Elevation Satellite
About $232.1 million was budgeted for the mission, which has been
under preparation for four years.
University of Texas at Austin Aerospace Engineering Professor Bob
Schutz headed a nationwide team who developed the satellite’s
orbit and the technical specifications for the laser system whose
reflected light will reveal ice, land and other Earth changes over
time. This Geoscience Laser Altimeter System (GLAS) will be the
Dec. 19 mission’s sole payload.
The mission is well poised to gather just the kind of data sorely
needed by the academics, energy experts and environmentalists who
attended President Bush’s meetings on climate change research
last week. The effect of global warming on net loss vs. gain of
polar ice mass remains to be established. The same elevated temperatures
that cause the ice sheets to melt around their edgesraising
sea level—might also lead to a globally moister climate. This
in turn could result in more precipitation everywhere, including
over the ice sheet themselves, which could actually thicken toward
the middle, offsetting the sea water gain from melting peripheral
ice. Determining exactly what happens is a vital first step toward
understanding the consequences—and setting policy.
“Our measurements will set the standard for future measurements,
and our discoveries will become a basis for policy-making,”
Schutz says. “The innovation that gives our instrument its
unprecedented accuracy is the use of laser technology. That’s
what gives it the ability to operate over the ice sheets, especially
over the sloping areas of the ice sheets, which are out near the
edges where melting is taking place. Radar altimeters, which have
been used in the past, are unable to generate comparable accuracy,
especially for those sloping regions.”
The GLAS instrument will emit 40 pulses of laser light per second as ICESat hurtles through space at 16,000 miles per hour, 370 miles above Earth's surface, making 15 passes over the Arctic and Antarctic ice sheets daily.
Among the questions the ICESat/GLAS team wants to answer:
- Are the Greenland and Antarctic ice sheets growing or shrinking?
- Will the ice sheets thin, or thicken in a warmer climate?
- How fast is sea level rising?
ICESat will measure details of the planet’s all-important
polar ice sheetsand, secondarily, land elevations, vegetation
cover and ocean icethroughout the year, while taking into
account the influence of such important atmospheric phenomena as
clouds and aerosols. Its goal is to gather accurate data about a
host of climate variables and their near- and far-range effects,
information that will improve understanding and protect the planet
against changes in weather patterns that have climatologists concerned.
“The satellite’s information will stream in over the
Internet in the form of distance measurements recording the distance
from the satellite to a point on the surface,” Schutz says.
“By comparing repeat profiles, we determine surface change.
And then we’ll take a series of those numbers to get a profile
of the surface. We’re particularly interested in looking at
the changes in thickness of both ice sheets: Greenland and Antarctic.”
Information ICESat/GLAS generates will help identify the annual
net change in polar ice mass believed partly responsible for a global
sea level rise of about 0.8 inch every 10 years. The increase, small
in any given year, is nonetheless sufficient over a period of several
decades to seriously affect low-lying coastal regions through shoreline
retreat and flooding.
GLAS instrument will be the ICESat mission’s sole payload
on Dec. 19.
The launch, from Vandenberg Air Force Base, Calif., is the first
in an anticipated series of multi-year ICESat missions stretching
over decades. Cutting-edge Global Positioning System technology
aboard ICESat will track its position at every instant it orbits
some 370 miles above Earth’s surface. A ground-based network
of laser ranging stations, including the university’s McDonald
Observatory, will augment the GPS positioning.
At the mission’s heart is GLAS, the instrument that will
determine the distance between the satellite and Earth’s features
as ICESat traces out a uniform pattern over the globe each 180 days.
GLAS works by sending out short pulses of laser light—at a
rate of 40 per second—and measuring the time it takes them
to bounce back after striking their target—be it the Antarctic
Ice Sheet, a cloud, an erupting volcano or a swath of Brazilian
rain forest. The higher a feature’s elevation, the less time
it will take the laser beam to make its round trip.
GLAS will illuminate spots on Earth’s surface with a diameter
of 230 feet, separated by a distance of 560 feet. Two wavelengths
of light are emitted simultaneously: a “long” infrared
one for surface targets and a shorter, green one to chart atmospheric
interactions. GLAS then converts the data from time into distance
information. Using complex mathematical formulae that compensate
for the ICESat satellite’s 16,000 miles per hour forward motion
and regular changes in its path, researchers will be able to plot
minute changes in surface feature elevation to an accuracy of four
inches in 370 miles.
Information collected by GLAS during its three- to five-year lifespan
will be analyzed by researchers at the Center for Space Research
(CSR) at The University of Texas at Austin. The CSR will calibrate
GLAS at White Sands, N.M., using ground truth instrumentation developed
at The University of Texas at Austin.
The profiles obtained will ultimately be used to create topographical
The ICESat mission crowns a 10-year collaboration between investigators
at the Center for Space Research and NASA Goddard Space Flight Center,
with additional support from personnel at academic institutions
and private corporations throughout the United States.