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CloudSat: How Clouds Relate to Climate

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NASA artisit's view of CloudSat in orbit

CloudSat is designed to clarify the relationship between clouds and climate. It will fly in formation and coordinate measurements with other NASA spacecraft in the A Train.

CloudSat will use a millimeter-wavelength radar to measure the altitude and properties of clouds. Slicing a vertical cross-section of the atmosphere, the satellite's cloud profiling radar will relay meteorological data including cloud-layer thickness, cloud top and base altitudes, cloud optical properties, and cloud water and ice content.

CloudSat will improve numerical weather prediction models by directly measuring cloud properties from the top of the atmosphere to the surface of the Earth. It will help meteorologists:

improve weather forecasts through better numerical prediction models by directly measuring cloud properties from the top of the atmosphere to the surface of the Earth.

mitigate natural hazards with new information from its radar penetrates thick clouds increasing the accuracy of severe storm, hurricane, and flood warnings.

manage water resources by linking climate conditions such as El Nino and La Nina with hydrological processes that affect the occurrence of regional drought and incidences of severe weather.

understand the relationship of climate to the chemical, hydrological, and dynamic processes that maintain Earth's energy balance. Data from CloudSat will help us understand how the ability of clouds to heat and cool our planet determines Earth's energy balance.
Why CloudSat?

CloudSat has a number of important goals in its mission, including:

improving weather prediction, help mitigate natural hazards, aid water resource management, clarify climatic processes, and develop critical spacebornetechnologies.

filling an observational gap in existing and planned spacebornesurveillance systems.

distributing data to civilian and military weather forecast agencies.

demonstrating active sensor technology for future scientific, civilian, and tactical weather forecast systems.

providing an opportunity to validate and improve theenvironmental data records being proposed for the National PolarOrbiting Environmental Satellite System (NPOESS).

demonstrating innovative, new processes to reduce mission costs and development time.
Advancing technology:

CloudSat is spurring innovative technology including:

Spacecraft formation flying techniques
High-power millimeter-wave radar
Quasi-optical radar transmission lines
Integrated geophysical retrieval algorithms
In the A Train:

The CloudSat payload is a millimeter-wave radar.

The satellite will fly in orbit around Earth in a tight formation with the CALIPSO satellite, which carries a backscattering lidar. In turn, the two satellites will follow behind the Aqua satellite in a looser formation. As a group, the satellites have been referred to as the A Train.

The combination of data from the CloudSat radar with coincident measurements from CALIPSO and Aqua provides a rich source of information that can be used to assess the role of clouds in both weather and climate.

Click to enlarge NASA artist concept of the A Train satellites above Earth

The environmental satellites Aura, Aqua, Terra, CloudSat, CALIPSO and PARASOL are referred to as the A Train in space because the caravan will resemble a train of satellites flying around Earth. The A-Train reference comes from a jazz tune, Take the 'A' Train, about riding a subway to New York City's Harlem, written in 1941 by Billy Strayhorn and made famous by jazz maestro Duke Ellington. [ lyrics »» ]

In orbit, the sequence of six satellites in the convoy runs from Aqua to Aura. Each is part of NASA's fleet of Earth watching satellites that the space agency refers to as the Earth Observing System.

The ability to reduce risk is a benefit of flying satellites in formation. Sets of less costly, less expensive, less complex satellites means that failure of one does not kill an entire mission.

Formation flying:

Formation flying is a station keeping exercise that enables CloudSat to track the orbit of CALIPSO in a very precise way.

The CloudSat orbit will be adjusted and monitored to keep it a fixed distance from CALIPSO. The spacecraft will be controlled so both sets of sensors view the same ground track for the majority of the time. The average separation between the satellites will be about 286 miles which corresponds to approximately 60 seconds delay between lidar and radar measurements.

Formation flying with CALIPSO provides direct overlap of the lidar footprint within the footprint of the radar most of the time.

CloudSat radar:

The CloudSat payload is a 94-GHz Cloud Profiling Radar (CPR). Associated with it are the payloads of the other A Train satellites including the dual wavelength lidar system aboard CALIPSO and the CERES, AIRS, AMSR and MODIS payloads aboard Aqua.

The CPR was developed jointly by NASA's Jet Propulsion Laboratory (JPL) and the Canadian Space Agency (CSA).

NASA explained that the choice of the 94 GHz radar frequency was a trade-off between sensitivity, antenna gain, atmospheric transmission, and radar transmitter efficiency. Sensitivity and antenna gain increase with frequency while atmospheric transmission and transmitter efficiency decrease with frequency. Since the size and shape of a space satellite constrain antenna size, a frequency of 94 GHz is a good compromise. At the same time, an international frequency allocation at 94 GHz has been set aside for spaceborne radar use. The choice of frequency means a small percentage of the time when very thick clouds or heavy precipitation is present, the radar will not be able to penetrate to the cloud base.

CloudSat orbit:

The 1,543-lb. CloudSat is likely to work three years in the same sun-synchronous, 438-mi.-high orbit of the Aqua satellite.

CloudSat will be launched on the same Delta rocket as CALIPSO from Vandenberg Air Force Base, California.

Data from the satellite will transmitted to Earth ten times a day and processed by the Cooperative Institute for Research in the Atmosphere (CIRA) at Colorado State University (CSU).

JPL is responsible for mission operations and payload development. Ball Aerospace built the spacecraft. Radar calibration will use the U.S. Department of Energy (DOE) Cloud and Radiation Test bed (CART), NASA aircraft, and university and government research facilities including University of Utah, Pennsylvania State University, GKSS in Germany, NOAA Environmental Technology Lab, Atmospheric Environmental Services (AES) in Canada, and Communication Research Lab (CRL) in Japan.