The CLARREO imperative to initiate an unprecedented, high accuracy record of climate change that is tested, trusted and necessary to provide sound policy decisions can only be achieved through advances in the current state of satellite sensor calibration. Accuracy requirements and attributes of a climate monitoring system are outlined in the recent "Achieving Satellite Instrument Calibration for Climate Change" (ASIC³) report. As stated in ASIC³, “Design of climate observing and monitoring systems must ensure the establishment of global, long-term climate records that are of high accuracy, tested for systematic errors on-orbit, and tied to irrefutable international standards maintained in the U.S. by the National Institute of Standards and Technology (NIST).”

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.

Operational principle for CLARREO RS reference intercalibration with sensors on JPSS and in cross-track data taking mode, e.g. VIIRS. CLARREO RS measurements (shown in red) are matched in time, viewing geometry, and spatially to cross-track observations by VIIRS (shown in green). The on-orbit data matching is enabled by CLARREO ability to point its RS instrument in two dimensions (azimuth and elevation angles).