Take NASA's Ice, Cloud and land Elevation Satellite (ICESat), for instance, which uses lasers to meticulously measure Earth's polar ice sheets, clouds, mountains and forests. ICESat recently resumed measurements with its Geoscience Laser Altimeter System (GLAS), which periodically pierces the sky with short pulses of green and infrared light about 40 times a second. The reflected light bounces back to the satellites one-meter telescope, which calculates precise elevations by measuring the travel time of laser pulses.

In this image, scientists and engineers with the Center for Space Research at the University of Texas at Austin photographed ICESat laser pulses in the sky and on the ground at Bonneville Salt Flats in Utah on Sept. 30. The series of green, near-circular spots is caused by GLAS's green laser light as it illuminates thin clouds and aerosols in the atmosphere. The spots captured here in an eight-second camera exposure occurred in intervals of less than three hundredths of a second, each separated by a distance of 170 meters. The bright streak slicing upwards through the image is from an airplane looking down on Earth to photograph the green and infrared light on the ground. The smaller, white spots are stars.

Credit: NASA/University of Texas