SI-Traceability of the Atmospheric Infrared Sounder Version 5 Level 1B Radiances

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on May 4, 2002. The AIRS was designed to measure atmospheric temperature and water vapor profiles and has demonstrated exceptional radiometric and spectral accuracy and stability in-orbit. The International System of Units (SI)-traceability of the derived radiances is achieved by transferring the calibration from a Large Area Blackbody (LABB), and Space View Source (SVS), to the On-Board Calibrator (OBC) blackbody during preflight testing and frequent on-board calibration. The AIRS also provides a full aperture space view every scan for offset calibration. AIRS nonlinearity and polarization calibration coefficients are based on pre-flight testing and have been among the highest uncertainty sources in the calibration. Recent methods using on-board data has improved our understanding of the magnitude and uncertainty of these terms. An estimate of the system radiometric accuracy (defined as the uncertainty relative to SI-traceable standards), is made based for the Version 5 AIRS L1B radiance product. SI-traceability and quantification of the radiometric uncertainty is critical to reducing biases in reanalysis products and radiative transfer models that use AIRS data, as well as establishing the suitability of AIRS as a benchmark for radiances established in the early 2000’s.