Updates to the absolute radiometric accuracy of the AIRS on Aqua

Abstract

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 accuracy is achieved by transferring the calibration from a Large Area Blackbody (LABB) to the On-Board Calibrator (OBC) blackbody during preflight testing and frequent on-board calibration. The LABB theoretical emissivity is in excess of 0.9999 and temperature uncertainty is less than ±60 mK. The LABB emitted radiance is NIST traceable through thermistors located on the internal surfaces. The AIRS also provides a full aperture space view every scan for offset calibration. AIRS nonlinearity and polarization calibration coefficients were based on pre-flight testing and have been among the highest uncertainty sources in the calibration. A recent method using on-board space view data has reduced the uncertainty of the polarization coefficients and use of separate A side and B side data from pre-flight testing has reduced the uncertainty of the nonlinearity estimates. An update to the system radiometric uncertainty is made based on the new data and includes other refinements and is presented in this paper. This paper does not address the stability of the AIRS radiances in orbit that is usually determined by comparison with surface observations.