NASA Logo - National Aeronautics and Space Administration

The CLARREO Vision Outlined in the 2007 Decadal Survey: Achieving Climate Change Absolute Accuracy in Orbit

The NRC Decadal Survey concluded that the single most critical issue for current CLARREO BAMS Cover climate change observations was their lack of accuracy and low confidence in observing the small climate change signals over long decade time scales1,2,3,4,5. Observing decadal climate change is critical to assessing the accuracy of climate model projections6,7,8 as well as to attributing climate change to various sources6. Sound policymaking requires high confidence in climate predictions verified against decadal change observations with rigorously known accuracy.

The Challenge:

The need to improve satellite data accuracy has been expressed in U.S. interagency reports4,5, international observing system plans9,10, and the Global Space-Based Intercalibration System11,12. Common challenges identified in these documents include uncertain long-term calibration drift, insufficient absolute accuracy, gaps in observations, and increased uncertainty even for overlapped and intercalibrated instruments13.


The Climate Absolute Radiance and Refractivity Observatory addresses these challenges by providing improved absolute accuracy in global satellite observations that can be traced continuously on orbit to international physical standards such as the Systeme Internationale (SI) standards for seconds, kelvins, and watts. CLARREO observations fill a critical need for unambiguous climate change measurements with an unprecedented level of accuracy. The mission also provides the first orbiting radiometers with accuracy sufficient to serve as reference calibration standards for other space sensors, essentially serving as a "NIST in orbit". This improves the accuracy, by a factor of 5 to 10, and relevance of a wide range of spaceborne instruments for observing Earth's changing climate.

The Overarching CLARREO SCIENCE OBJECTIVE: Make highly accurate and SI-traceable decadal change observations sensitive to the most critical but least understood climate radiative forcings, responses, and feedbacks.

Critical Observations of Climate Change:

  • The climate benchmarks established by CLARREO are critical for assessing changes in the Earth system as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. CLARREO data will be used to test and validate climate models.
  • CLARREO benchmarks are obtained from direct measurements of the Earth's complete thermal infrared spectrum (IR), the complete spectrum of solar radiation reflected by the Earth and its atmosphere (RS), and radio occultation (RO) from which accurate temperature profiles are derived. IR, RS, and RO measurements provide information on the most critical but least understood climate forcings, responses, and feedbacks associated with the vertical distribution of atmospheric temperature and water vapor (IR/RS/RO), broadband reflected (RS) and emitted (IR) radiative fluxes, cloud properties (IR/RS), and surface albedo (RS), temperature (IR), and emissivity (IR).
  • CLARREO provides the first spectral observations of the far-infrared, which includes 50% of the Earth's energy emitted to space and contains most of the water vapor greenhouse effect.
  • CLARREO's ability to establish a reference calibration standard for sensors in Earth's orbit will improve weather forecasting and data assimilation, and will improve the accuracy of a wide variety of climate-relevant observations including land processes, atmospheric state variables, aerosols and trace gases, and surface temperature.
  • CLARREO provides accurate spectral surface reflectance for selected sites and advanced hyperspectral retrievals.


  1. NRC, 2007: Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. National Academy Press, 428 pp.
  2. Trenberth, K.E. and Coauthors, 2013: Challenges of a sustained climate observing system. Climate Science for Serving Society: Research, Modeling and Prediction Priorities, G. R. Asrar and J. W. Hurrell, Eds., Springer, 13–50.
  3. Trenberth, K. E., and J. T. Fasullo, 2010: Tracking Earth’s energy. Science, 328, 316–317.
  4. Ohring, G.B., B. A. Wielicki, R. Spencer, B. Emery, and R. Datla, 2005: Satellite instrument calibration for measuring global climate change: Report on a workshop. Bull. Amer. Meteor. Soc., 86, 1303–1313.
  5. Ohring, G. B., Ed., 2007: Achieving satellite instrument calibration for climate change (ASIC3). NOAA, 142 pp.
  6. Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. Averyt, M. M. B. Tignor, and H. L. Miller Jr., Eds., 2007: Climate Change 2007: The Physical Science Basis. Cambridge University Press, 996 pp.
  7. Masson, D., and R. Knutti, 2011: Spatial-scale dependence of climate model performance in the CMIP3 ensemble. J. Climate, 24, 2680–2692.
  8. Stott, P. A., and J. A. Kettleborough, 2002: Origins and estimates of uncertainty in predictions of twentyfirst century temperature rise. Nature, 416, 723–726.
  9. GEO, 2005: The Global Earth Observation System of Systems (GEOSS) 10-Year Implementation Plan. Group on Earth Observations, 11 pp.
  10. Global Climate Observing System, 2011: Systematic observation requirements for satellite-based data products for climate: 2011 update. GCOS-154, WMO, 128 pp.
  11. GSICS, 2006: Implementation plan for a Global SpaceBased Inter-Calibration System (GSICS). WMOCGMS, 22 pp.
  12. Goldberg, M., and Coauthors, 2011: The Global SpaceBased Inter-Calibration System (GSICS). Bull. Amer. Meteor. Soc., 92, 467–475.
  13. GEO, 2010: A quality assurance framework for Earth observation: Principles, version 4. Group on Earth Observations, 17 pp.