Since October 8, UW¿Madison's lidar group has helped NASA test its ICEsat, the Ice, Cloud and land Elevation Satellite that is studying changes in polar ice thickness and extent. UW's High Spectral Resolution Lidar measures the same atmospheric quantities measured by the Geoscience Laser Altimeter System (GLAS) on the satellite and when ICEsat is directly overhead about every eight days, the two laser beams can meet to calibrate the GLAS. The UW instrument operates at the same wavelength as NASA's instrument.
The two instruments both measure the heights of clouds and aerosols, such as haze and particles in smoke, in the atmosphere from precise measurements of the travel time of the laser pulses and, in the satellite's case, calculated against its orbit and instrument orientation.
Both instruments are used in climate studies; the UW lidar is used particularly to finely tune numerical models of climate and weather, leading to increasingly better weather forecasts and a better understanding of Earth's climate.
Calibration tests are dependent on the weather to work well. Thick clouds keep the beams from meeting. The scientists hope for cirrus clouds or haze for the maximum effect, and best test¿something we can see through, but that gives a nice signal.
NASA's Goddard Space Flight Center tentatively plans to test the GLAS this Friday afternoon, November 7. If the laser being tested is still on in mid-November¿it may be turned off by then¿the satellite will pass almost directly over Madison on the evening of November 11. Times will be known the day of the pass. If the weather is right, the UW lidar will be seen as a green beam and the satellite as a green flash, as captured in the video on the UW Lidar
