CloudSat Key CloudSat Facts Joint with Canada Orbit: Type: Sun-synchronous Altitude: 705 km Inclination: 98.2° Period: 99 minutes Repeat Cycle: 16 days Dimensions: 2.3 m × 2.3 m × 2.8 m CloudSat URLs Mass: 999 kg cloudsat.atmos.colostate.edu essp.gsfc.nasa.gov/cloudsat Power: 700 W cloudsat.cira.colostate.edu Downlink: S-band to U.S. Air Force antenna network Mission Life: 22 months Summary Design Life: 3 years CloudSat will study clouds in detail to better characterize the role they play in regulating Earth’s climate. CloudSat Contributors will provide the first direct, global survey of the vertical structure and overlap of cloud systems and their liquid- Canadian Space Agency (CSA), U.S. Air Force (USAF), U.S. Department of Energy (DOE) and ice-water contents. Data returned should lead to improved cloud representations in atmospheric models, which should help improve the accuracy of weather fore- casts and climate predictions made using these models. Launch Date and Location: April 28, 2006 (shared launch with Instrument CALIPSO), from Vandenberg Air Force Base, California Cloud Profiling Radar (CPR) Vehicle: Delta II rocket Points of Contact • CloudSat Principal Investigator: Graeme Stephens, Relevant Science Focus Areas Colorado State University (see NASA’s Earth Science Program section) • CloudSat Deputy Principal Investigator: Deborah • Climate Variability and Change Vane, NASA Jet Propulsion Laboratory/California • Weather Institute of Technology Related Applications (see Applied Sciences Program section) Other Key Personnel • Aviation • CloudSat Program Scientist: Donald Anderson, Also valuable for weather prediction NASA Headquarters • CloudSat Program Executive: Steve Volz, NASA Headquarters CloudSat Science Goals • CloudSat Project Manager: Thomas Livermore, Profile the vertical structure of clouds:Understanding the NASA Jet Propulsion Laboratory/California Institute vertical structure of clouds is fundamentally important to of Technology improving our understanding of how clouds affect both the local and large-scale environment. Mission Type Measure the profiles of cloud liquid water and ice water Earth Observing System (EOS) Exploratory Mission content: These two quantities—predicted by cloud process (Earth System Science Pathfinder) and global scale models alike—determine practically all Earth Science Reference Handbook [ Missions: CloudSat ] 125 other cloud properties, including precipitation and cloud CPR optical properties. Cloud Profiling Radar Measure profiles of cloud optical properties:These mea- CPR is a 94-GHz radar with 500-m vertical resolution. The radar sends out a pulse and receives a return signal. Because the 94- surements, when combined with water and ice content GHz signal is not strongly attenuated by most clouds, the radar information, provide critical tests of key cloud process should be able to detect more than 90% of all ice clouds and parameterizations and enable the estimation of flux pro- 80% of all water clouds. files and radiative heating rates through the atmospheric column. CloudSat will utilize a 94-GHz Cloud Profiling Radar to obtain measurements of cloud properties. Cloud radars now operate routinely or quasi-routinely at a number CloudSat Mission Background of surface sites worldwide and are also deployed on a number of research aircraft. Measurements collected by Clouds and their properties are inadequately represented these instruments provide a rich heritage for the CloudSat in climate models, leading to continued uncertainty in radar. the prediction of global warming with increasing carbon Because clouds are weak scatterers of microwave dioxide (CO2). Even small changes in abundance or radiation, the overriding requirement on the radar is to distribution of clouds can profoundly alter the climate achieve the maximum possible sensitivity and hence response to changes in greenhouse gases. Clouds also maximize cloud detection. Sensitivity is primarily de- influence climate by affecting the efficiency at which the termined by radar-received power and noise level, and hydrological cycle operates. optimizing this sensitivity involves a careful tradeoff One of the main reasons model predictions of cli- among competing and conflicting factors, including the mate warming vary from model to model is the different cloud backscattering properties, the vertical resolution, ways models specify vertical cloud distributions and atmospheric attenuation, available power delivered to the overlap. The vertical distribution and overlap of cloud system, the orbit altitude, and radar technology. Increasing layers directly determine both the magnitude and vertical the antenna size and increasing transmitter output power profile of heating in the atmosphere. The heating by high are both ways to increase the power received. The antenna cloud layers in the tropical atmosphere exerts a dominant diameter of 1.85 m is limited by launch constraints. The influence on the large-scale, ‘Hadley’ circulation of the transmitter power is also limited by both the transmitter atmosphere. The vertical distribution of clouds assumed in technology and the power-supply capability of the space- models also influences the predicted precipitation. Direct craft. measurements of the vertical structure of clouds have, The amount of power received is also strongly until now, been limited to a few ground-based sites. influenced by the cloud reflectivity and atmospheric at- CloudSat will provide the observations necessary to tenuation. Cloud reflectivity increases with increasing advance our understanding of these issues. It will provide radar frequency but atmospheric attenuation becomes the first direct measurements of cloud vertical structure on prohibitive at higher frequencies. From these consider- a global basis. CloudSat will also measure the profiles of ations, the operating frequency of 94 GHz is an optimum cloud liquid-water and ice-water content (microphysical compromise and provides an increase of more than 30 dB properties) and will match these microphysical properties over the 14-GHz Tropical Rainfall Measuring Mission to cloud optical properties. This matching is a critical test (TRMM) radar. An international frequency allocation of of key parameterizations in models that enable calculation 94 GHz has been established for spaceborne radar use. of flux profiles and radiative heating rates throughout the Sensitivity is also related to the pulse length. The atmosphere. radar uses 3.3-µs pulses providing cloud and precipita- CloudSat data will provide a rich source of informa- tion information with a 500-m vertical range resolution tion for evaluating cloud properties derived from other between the surface and 25 km. The radar measurements satellite data. CloudSat will fly as part of the A-Train of along-track are averaged by the on-board data processor satellites including four other NASA missions—Aqua, over 0.16 s intervals, producing an oblong effective foot- Aura, Cloud-Aerosol Lidar and Infrared Pathfinder print of 1.4 km × 1.8 km. The radar data can be further Satellite Observations (CALIPSO), and eventually the averaged in ground processing to 0.48 s, increasing the Orbiting Carbon Observatory (OCO)—as well as a French effective footprint in the along-track dimension to 3.8 km. Centre National d’Etudes Spatiales (CNES) mission This provides the averaging needed to achieve the required called Polarization and Anisotropy of Reflectances for sensitivity. Atmospheric Sciences coupled with Observations from CPR will be sensitive enough to detect the majority a Lidar (PARASOL). This combination of observations of clouds that significantly affect the radiation budget and offers an unprecedented resource for exploring aerosol- critical elements of the water budget of the atmosphere. chemistry-cloud interactions. CPR is expected to detect 90% of all ice clouds and 80% 126 [ Missions: CloudSat ] Earth Science Reference Handbook of all water clouds. Other sensors that are flying or will fly as part of the A-Train formation, particularly the Moderate Resolution Imag- Key CPR Facts ing Spectroradiometer (MODIS) on Aqua and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on CALIPSO, are Heritage: Aircraft and ground-based expected to augment the cloud-detection capabilities of CPR. 94-GHz radars Likewise, CPR will improve the cloud-detection capabilities of Nadir-pointing 94-GHz radar measures MODIS. This is but one of many examples of the value of the cloud reflectivity vs. altitude along nadir synergistic measurements enabled by the A-Train formation. track If CloudSat were flying in isolation, it would probably reside Single science operation mode at a lower altitude, similar to that of TRMM. This would give CPR Vertical resolution: ~500 m from 0 to even greater sensitivity and improved ability to detect clouds. 25 km altitude However, because CloudSat has chosen to be part of the A-Train Transmits 3.3-µs monochromatic formation, it flies at a higher altitude. This compromise still gives pulses CPR excellent cloud-detection capabilities to achieve CloudSat’s Horizontal resolution: ~1.4 km mission objectives, while also enabling maximum synergism with Duty cycle: 100% the other A-Train missions. Technical Resource Allocations: The antenna subsystem consists of the collimating antenna Mass: 260 kg and the Quasi-Optical Transmission Line (QOTL). The antenna, Power: 270 W constructed of composite graphite material, meets the challenge of low surface roughness (less than an RMS of 0.05 mm over the Data