Clouds exert an enormous influence on our weather and climate. They are the key element of Earth’s hydrological cycle, bringing water from the air to the ground and from one region of the globe to another. Clouds also dominate the energy budget of Earth through their influence on the exchange of solar and thermal energy within the atmosphere and between the atmosphere, hydrosphere, land surface, biosphere, and space.
Because clouds have such a large impact on Earth’s radiation budget, even small changes in cloud abundance or distribution could alter the climate more than the anticipated changes in greenhouse gases, anthropogenic aerosols, or other factors associated with global change. Changes in climate that are caused by clouds may in turn give rise to changes in clouds due to climate: a cloud-climate feedback. These feedbacks may be positive (reinforcing the changes) or negative (tending to reduce the net change), depending on the processes involved. These considerations lead scientists to believe that the main uncertainties in climate model simulations are due to the difficulties in adequately representing clouds and their radiative properties.
CloudSat was selected as a NASA Earth System Science Pathfinder satellite mission in 1999 to provide observations necessary to advance our understanding of cloud abundance, distribution, structure, and radiative properties. Since 2006, CloudSat has flown the first satellite-based millimeter-wavelength cloud radar—a radar that is more than 1000 times more sensitive than existing weather radars. Unlike ground-based weather radars that use centimeter wavelengths to detect raindrop-sized particles, CloudSat's radar allows us to detect the much smaller particles of liquid water and ice that constitute the large cloud masses that make our weather.
CloudSat was co-manifested with the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite aboard a Delta II rocket for its launch on 28 April 2006. In a series of maneuvers, CloudSat and CALIPSO joined three satellites already in orbit ( Aqua, PARASOL, and Aura) to form a constellation of satellites known as the A-Train on 1 June 2006. The satellites fly in a nearly circular orbit with an equatorial altitude of approximately 705 km. The orbit is sun-synchronous, maintaining a roughly fixed angle between the orbital plane and the mean solar meridian. CloudSat maintains a close formation with Aqua and a particularly close formation with CALIPSO, providing near-simultaneous and collocated observations with the instruments on these two platforms. Combined data products are in development using data streams from CloudSat + Aqua and CloudSat + CALIPSO.
Science leadership for CloudSat is provided by the Principal Investigator, Prof. Graeme Stephens of Colorado State University, in cooperation with the CloudSat Science Team. NASA's Jet Propulsion Laboratory provides overall project and mission management and development and implementation of CloudSat's instrument, the Cloud Profiling Radar. A more extensive description of CloudSat mission participants and their roles is given on the Partners page.