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The CLARREO (Climate Absolute Radiance and Refractivity Observatory) is a high priority NASA Decadal Survey mission recommended by the National Research Council in 2007.[1] The CLARREO mission may provide a metrology laboratory in orbit for the purpose of accurately quantifying and attributing Earth's climate change (see List of climate research satellites). CLARREO's observations could be used to detect climate trends and to test, validate, and improve prediction by climate models. The mission also might provide the first orbiting radiometers with accuracy sufficient to serve as reference calibration standards for other spaceborne sensors. [2]

The mission concept[edit]

CLARREO is currently in an extended planning phase or "Pre-Phase A," where the mission and science teams are funded to continue advancing the science of CLARREO, explore alternative implementation strategies, and reduce technical risk.[3]

Below is the most recent mission concept presented at the Mission Concept Review in November 2010.[4] CLARREO is currently envisioned to consist of four observatories on two dual-manifested launches on Minotaur IV+ vehicles.

Current CLARREO Mission Concept
  • Four Observatories, two dual-manifested launches on Minotaur IV+ vehicles
    • July 2018: Two infrared observatories, each with GNSS-RO
    • May 2020: Two reflected solar observatories
  • 609 km polar orbits (90 degree inclination)

The science behind CLARREO[edit]

CLARREO could make highly accurate decadal change observations that are traceable to International Systems of Units (SI) standards. These observations are sensitive to the most critical but least understood climate radiative forcings, responses, and feedbacks, such as:

  • Infrared spectra to infer temperature and water vapor feedbacks, cloud feedbacks, and decadal change of temperature profiles, water vapor profiles, clouds, and greenhouse gas radiative effects
  • GNSS-RO to infer decadal change of temperature profiles
  • Solar reflected spectra to infer cloud feedbacks, snow/ice albedo feedbacks, and decadal change of clouds, radiative fluxes, aerosols, snow cover, sea ice, and land use[5]

Reference intercalibration[edit]

CLARREO RS measurements (in red) are matched in time, viewing geometry, and spatially to cross-track observations by VIIRS (in green). On-orbit data matching is enabled by CLARREO's ability to point its RS instrument in two dimensions.

Current satellite-based sensors are not designed to meet the accuracy requirements of CLARREO. Many sensors used for climate measurements were designed to meet operational weather needs and are not optimized for climate sampling. These sensors, along with older instruments designed for climate, lack the ability to test for systematic errors on orbit. The CLARREO mission is designed to meet these goals through careful consideration of the instrument design, calibration traceability at all stages of development and operation, and spectral, spatial, and temporal sampling focused specifically on the creation of climate records. With development of new cross-calibration methodology there is a possibility that CLARREO may serve as an in-orbit standard to provide reference intercalibration for missions like the broadband Clouds and the Earth's Radiant Energy System (CERES), operational sounders including the Cross-track Infrared Sounder (CrIS) and Infrared Atmospheric Sounding Interferometer (IASI), and imagers such as the Visible Infrared Imaging Radiometer Suite (VIIRS) and Advanced Very High Resolution Radiometer (AVHRR).[6]

CLARREO selection[edit]

The 2007 National Research Council (NRC) Decadal Survey report,[7] "Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond," provides the basis for the future direction of NASA’s space-based Earth observation system. Missions were ranked according to scientific merit, contributions to long-term observational records, societal benefits, affordability, and technological readiness. The four missions recommended for earliest implementation by NASA were classified as “Tier 1” missions and included CLARREO. The NRC Decadal Survey concluded that the single most critical issue for current climate change observations was their lack of accuracy and low confidence in observing the small climate change signals over decade time scales. CLARREO observations of climate change on decadal scales address this issue by achieving the required levels of accuracy and traceability to SI standards for a set of observations sensitive to a wide range of key climate change observations.

Decadal Survey recommendations represent the community's input on the future direction of space-based Earth science; therefore, NASA will continue to engage the scientific community to refine mission requirements during the planning for CLARREO.

The CLARREO Team[edit]

CLARREO is recommended as a joint NASA/NOAA mission.[8] NOAA will contribute the total and spectral solar irradiance measurements and the Earth energy budget climate data records by flying the Total Solar Irradiance Sensor (TSIS) and the Clouds and the Earth’s Radiant Energy System (CERES) sensors. The NASA portion involves the measurement of spectrally resolved thermal IR and reflected solar radiation at high absolute accuracy.

A NASA team led by Langley Research Center with contributions from other NASA Centers, government organizations, academia, and NASA HQ successfully developed a feasible mission concept that achieved all science objectives. CLARREO was the first Earth Science Decadal Survey mission to fully pass its Mission Concept Review (MCR) on 11/17/10. [9] The MCR Board chair, Dennon Clardy, cited the exceptional working relationship among science, project management, and engineering as a major strength of the project, leading to a mission concept that was extremely mature for MCR. The team’s successful completion of this milestone demonstrated CLARREO's readiness to proceed into Phase A.

Societal benefits of CLARREO[edit]

CLARREO might provide the data necessary to accelerate decisions on public policy concerning climate change by 15 to 20 years. Earlier and better informed decisions would provide a large economic benefit to the United States and the world, estimated to be about 12 Trillion dollars (at 3% discount rate) over the next 40 - 60 years,[10] CLARREO possibly establishes a record with the high accuracy and information content necessary to detect long-term climate change trends and to test and systematically improve climate predictions. If it can reduce climate prediction uncertainties, CLARREO impacts: civil Government and military planning (i.e., Navy bases), disaster mitigation, response, and recovery (i.e., insurance industry), and U.S. international policy decisions.

The Science Value Matrix (SVM) – Potential benefit to other NASA missions[edit]

For a complex mission with multiple science objectives, the relative merits of competing goals are difficult to quantify. Without an objective means of calculating science benefit, a project team cannot effectively evaluate the cost/benefit of multiple engineering approaches. The CLARREO team developed the Science Value Matrix[citation needed] (SVM) in an attempt to solve this challenge by : an approach that quantitatively defines science value for key aspects of the mission such as measurement accuracy, orbit type, and record length. By defining relative science value across the broad climate objectives of CLARREO, the team provided a mechanism for optimizing science value relative to cost. Not only was the SVM used to evaluate options within the very broad trade space, it was also designed to be a management tool to be used over the project lifecycle. In an environment of increasingly cost-constrained budgets, the SVM provides teams with the opportunity to rapidly assess alternative implementation options. This tool is actively being used in Pre-Phase A to evaluate lower cost options for implementing a portion of the CLARREO science.[11]


  1. ^ National Research Council, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. National Academies Press, Washington, D.C., 426pp, 2007.
  2. ^ Wielicki et al., "Achieving Climate Change Absolute Accuracy," Bull. Amer. Meteor. Soc., pp. 1829 1519-1539, 2013.
  3. ^
  4. ^ "CLARREO Mission Overview 2011 (21 January 2011)". Retrieved 18 July 2012. 
  5. ^
  6. ^
  7. ^ National Research Council, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. National Academies Press, Washington, D.C., 426pp, 2007.
  8. ^
  9. ^
  10. ^ R. Cooke, B.A. Wielicki, D.F. Young, M. Mlynczak, "Value of Information for Climate Observing Systems," Environ. Syst. Decis., 12 pp., 201, DOI 10.1007/s10669-013-9451-8.
  11. ^

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