Monitoring climate from space: a metrology perspective

摘要

Application of the principles of metrology for the NASA Climate Absolute Radiance and Refractivity Observatory (CLARREO) infrared high spectral resolution measurements is presented, starting with the use of a Standard International (SI) reference source on orbit, developing uncertainty traceability for intercalibration to other spaceborne sensors, and finally tracing the direct effects of radiance uncertainty on climate products originating from state parameter retrievals. The Absolute Radiance Interferometer (ART) IR prototype employs an On-orbit Absolute Radiance Standard (OARS), developed under the NASA Instrument Incubator Program for CLARREO, for on-orbit calibration verification to better than 0.1 K 3-sigma. The OARS consists of a variable temperature, high emissivity blackbody with temperature calibration established to better than 16 mK on-orbit and provision for on-orbit emissivity monitoring. The temperature scale is established using miniature melt cells of Ga, H_2O, and Hg. Transferring the high accuracy of ARI measurements to other IR instruments, especially the high spectral resolution operational sounders (AIRS, CrIS and IASI), is an important objective of CLARREO. The mathematical approach to rigorous traceability of sampling uncertainties is explained and applied in simulations of the intercalibration process. Results show that it will be possible to make intercomparisons of better than 0.05 K 3-sigma with just 6 months of observations from a single CLARREO in true polar orbit. Finally, the effects of radiance perturbations representing realistic uncertainties (for the CrIS on Suomi NPP) on retrieved temperature and water vapor profiles are evaluated. The results demonstrate a stable, physically reasonable impact of Dual regression retrievals.