UW-Madison Lidar instruments will test NASA’s ICESat

Tonight (Oct. 8) at 8:45 p.m. Central time, NASA will test a laser instrument on the Ice, Cloud and Land Elevation Satellite (ICESat) using accurately calibrated instruments developed by the UW Lidar group and housed atop the Atmospheric, Oceanic and Space Sciences Building on UW–Madison’s south campus.

This test, which will produce a pulsing, ghostly green light, may be visible over Madison’s nighttime sky.

Both UW–Madison’s and NASA’s lasers measure the heights of clouds and aerosols in the atmosphere from precise measurements of the travel time of the laser pulses, calculated against the satellite’s orbit and instrument orientation. The UW instrument operates at the same wavelength as NASA’s instrument, so NASA can use it to calibrate their laser.

Ed Eloranta, part of UW–Madison’s Space Science and Engineering Center and principal investigator for the UW Lidar program, says his group’s High Spectral Resolution Lidar (HSRL) laser “is the best instrument in the world for this test.” This laser instrument directly measures the quantities it is hoped that NASA’s Geoscience Laser Altimeter System (GLAS) instrument on ICESat will measure.

With ICESat, NASA hopes to study how the polar ice sheets are changing. UW’s instruments are also used in climate studies, particularly to finely tune numerical models of climate and weather. SSEC’s Arctic HSRL, now working on the building’s roof, is slated for placement in the Arctic ice some time in 2005.

It is possible that Madison residents will have a visual treat during the test. The pale, ghostly green laser light is tested in a series of pulses. When the beams meet from the satellite and UW’s earth-based instruments, especially if the sky is hazy or high thin cirrus clouds are present, the beam will be brighter, and special effects may occur.

“The sight could be spectacular,” says Eloranta. “I’m hoping we can see something.”

Unlike many laser beams, these are completely safe.

The test is the first of several planned to happen about every eight days at about the same time each night. More information about the UW instruments is available on the Web: http://lidar.ssec.wisc.edu/.