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 (ICESat).

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 edges—raising 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 sheets—and, secondarily, land elevations, vegetation cover and ocean ice—throughout 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.

The 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 maps.

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.