13 Oct UW-Madison Laser Device to Study Polar Ice Caps
MADISON, WI – A laser device developed by the University of Wisconsin-Madison Lidar (Light Detection and Ranging) group was used to test NASA’s ICESat (Ice, Cloud and Land Elevation Satellite) laser device. Lidar’s Arctic HSRL (High Spectral Resolution Lidar) instrument was chosen for the test because it operates on the same wavelength as the ICESat. NASA will use the ICESat instrument to study the climate and changing polar ice sheets in the Arctic.
Lidar, which is used by both the Arctic HSRL and the ICESat, allows scientists to measure distance, speed, rotation, and chemical composition and concentration of a remote target. The target can be a clearly defined object, such as a vehicle, or a diffuse object such as a smoke plume or clouds.
Both UW-Madison’s and NASA’s lasers measure the heights of clouds and aerosols in the atmosphere from precise measurements obtained by laser pulses calculated against the satellite’s orbit and instrument orientation. The Arctic HSRL operates at the same wavelength as NASA’s instrument and makes calibrated measurements of atmospheric scattering characteristics. It can provide a more direct comparison check on the calibration of the satellite instruments and similar instruments.
“Our next step is to compare the two measurements to see how well the satellite calibration and satellite retrieval algorithms are working,” said Ed Eloranta, senior scientist of UW Lidar Group. “We’re going to repeat this process for the next month or so; every eight days the satellite is going to come over us and each time it comes near enough to us it’s going to be steered to point at the building. We’ll make a series of measurements like this under different conditions.”
Arctic HSRL, now working on the roof of the UW-Madison’s Atmospheric, Oceanic and Space Sciences Building, is slated for placement in the Arctic ice some time in 2005.
According to Eloranta, the test results already look promising. “The ground instrument has been running almost continuously for the last three months and it performed well throughout the entire test; we got good data from the ground,” he said. “The initial test went over very well, we got good data on both ends and it looks like we’ll be able to do what we set out to do.”
ICESat is a small satellite with the ability to precisely measure height changes of polar ice sheets. It will allow scientists to get a precise look at the dynamics of the West Antarctic Ice Sheet, one of the least understood and most critical variables in the global climate change equation.
“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.
ICESat will emit pulses of green and infrared laser light at a rate of 40 times per second. The laser light will be reflected back into space and collected by a telescope aboard the satellite from its orbit 420 miles above the Earth. The distance from the satellite to a reflecting surface will be determined by measuring the time taken for the laser pulse to make the round trip.
NASA’s ICESat mission will provide multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information over polar areas. The ICESat satellite and its laser altimeter represent a new way to precisely measure change over the vast desert of ice. These 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.
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Jamie Lyn Hofmeister is a freelance technology writer and regular contributor to the Wisconsin Technology Network. She can be reached at jamie@wistechnology.com.