An environmental satellite operated jointly by NASA and the French Centre National d’Études Spatiales (CNES) carrying three instruments that monitor clouds and aerosols and their effects on weather, climate, and air quality 24 hours a day. It was launched together with CloudSat on 28 April 2006 into a Sun-synchronous orbit at approximately 750 km altitude, and flies in formation with four other satellites, known as the A-Train. In May 2017 the mission was extended for a further three years.

http://www-calipso.larc.nasa.gov/ A joint CNES and NASA mission to study the role that clouds and atmospheric aerosols play in regulating the Earth’s weather and climate.