ICESat Laser Spots over the Mojave Desert and Santa Rosa, New Mexico, USA
The Ice, Cloud, and land Elevation Satellite (ICESat) carries the Geoscience Laser Altimeter System (GLAS). This altimeter emits laser pulses at 1064 nm (infrared) and 532 nm (green) wavelengths 40 times per second from a nominal altitude of 600 km above the Earth.
The time-lapse picture on the left shows pulses emitted from the GLAS laser, photographed relative to the star field from the ground using a high-resolution digital camera in the Mojave Desert, California. The picture on the right shows the same phenomena above Santa Rosa, New Mexico. The movement of the satellite against the star field during the multiple second exposure is clear. The perceived blurring of the stars due to the motion of the Earth during the exposure is also evident. The image on the right shows thin clouds scattering the green light photons, producing the large spots seen on the left. The camera is slightly to the side of the ground track of the satellite as indicated by the spots being to one side of the image. Comparison of onboard laser pointing information and spot geolocation from photographs like this example allows calibration/verification of the GLAS precision attitude determination system. This information enables ICESat to gather elevation information on the Earth below with centimeter-level precision.
Images courtesy of Dr. J. Marcos Sirota, Claudia C. Carabajal, and David K. Mostofi, members of the ICESat Mission Team.