The Climate Absolute Radiance and Refractivity Observatory (CLARREO), a Tier-1 Decadal Survey mission recommended by the National Research Council, is a climate observation system designed to characterize Earth’s climate and how it is changing. CLARREO benchmarks will be derived from its spectrally resolved measurements of Earth-reflected shortwave (0.32 to 2.3 µm) and Earth-emitted thermal infrared (5 to 50 µm) radiation, and from radio occultation measurements from which accurate temperature profiles will be derived. CLARREO will provide the first orbiting radiometers with unprecedented accuracy sufficient to serve as reference calibration standards for other space sensors, essentially serving as a NIST in orbit. Accurate decadal-length records are essential for climate change detection and attribution and for rigorous testing of climate predictions. CLARREO data will provide a critical test of uncertainty in future climate change prediction and will contain the information needed to accelerate decisions on climate-related public policy by 15 to 20 years. Earlier and better-informed climate policy is economically valuable to the amount of about $12 Trillion over the next 40 to 60 years, which illustrates the value of having such a climate observing system in place.

The intercalibration capability of CLARREO will enable the improvement in accuracy of geophysical variable trends (e.g. cloud properties) retrieved using measurements from other satellite sensors, such as MODIS. Understanding how cloud properties are changing spatially and temporally is essential for understanding changes in Earth’s radiation budget and climate. Because typical process-specific studies that use these cloud properties focus on small spatial (e.g. instantaneous) and short time (e.g. hourly, diurnal) scales, satellite instrument calibration and cloud retrieval algorithms have been developed to minimize retrieval errors on these scales. However, measurement uncertainties at the pixel level may alias into global, decadal-scale trends of cloud properties, which are the scales relevant to climate change detection. The CLARREO accuracy framework is a rigorous, universal method that quantifies the impact of instrument uncertainty on the time to detect trends. In our studies, we are employing this accuracy framework to evaluate the impact that measurement calibration uncertainty has on our ability to detect cloud property trends.