Inter-comparison of NPP/CrIS radiances with VIIRS, AIRS, and IASI: a post-launch calibration assessment

Abstract

The Cross-track Infrared Sounder (CrIS) on the newly-launched Suomi National Polar-orbiting Partnership (Suomi NPP) is a Fourier transform spectrometer that provides soundings of the atmosphere with 1305 spectral channels, over 3 wavelength ranges: LWIR (9.14 - 15.38 μm); MWIR (5.71 - 8.26 μm); and SWIR (3.92 - 4.64 μm). An accurate spectral and radiometric calibration as well as geolocation is fundamental for CrIS radiance Sensor Data Records (SDRs). In this study, through inter- and intra-satellite calibration efforts, we focus on assessment of NPP/CrIS post-launch performance. First, we compare CrIS hyperspectral radiance measurements with the Atmospheric Infrared Sounder (AIRS) on NASA Earth Observing System (EOS) Aqua and Infrared Atmospheric Sounding Interferometer (IASI) on Metop-A to examine spectral and radiometric consistence and difference among three hyperspectral IR sounders. Secondly, an accurate collocation algorithm has been developed to collocate high spatial resolution measurements from the Visible Infrared Imager Radiometer Suite (VIIRS) within each CrIS Field of View (FOV). We compare CrIS spectrally-averaged radiances with the spatially-averaged and collocated pixels from the VIIRS IR channels. Since CrIS and VIIRS are onboard on the same satellite platform, the intra-satellite comparison will allow examining the radiometric difference between CrIS and VIIRS with scene temperatures, scan angles, and orbital position. In addition, given a high spatial resolution of VIIRS channels, the VIIRS-CrIS comparison results can access geolocation accuracy of CrIS that have relatively large FOVs (14 km at ndair) using high resolution VIIRS pixel (375m or 750m at nadir).