An Earth observing satellite that provides new insight into the role that clouds and atmospheric aerosols play in regulating weather, climate, and air quality has hit its target two billion times. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission, developed by NASA's Langley Research Center, Hampton, Virginia, and the French space agency Centre National d'Etudes Spatiales (CNES) has fired its lasers into the Earth's atmosphere over two billion times since its April 2006 launch.

Along with passive infrared and visible imagers, CALIPSO's lidar, an advanced laser ranging technique, probes the vertical structure and properties of thin clouds and aerosols over the globe. This unique, high-resolution, top-to-bottom profile created from pulses of laser light is used by the international science community to better understand the complicated interaction of clouds and aerosols — one of the least understood processes in the Earth system. As very few lasers of the type used on CALIPSO have been flown in the hostile environment of space, the satellite was designed and launched with two lidar units. The primary laser almost completed its three-year mission generating more than 1.6 billion pulses of light and 20 terabytes of data but had developed a slow leak in its pressure canister. The backup laser was switched on in early 2009 and nearly three years after launch, sent back its "first light" image on March 12. NASA and Ball Aerospace designed the lidar instrument; CNES and Thales Alenia Space, previously Alcatel Space, built the Proteus satellite platform.