Assessments of S-NPP CrIS Full Resolution SDR Radiometric and Spectral Accuracy

The Cross-track Infrared Sounder (CrIS) on Suomi National Polar-orbiting Partnership Satellite (S-NPP) is a Fourier transform spectrometer. In normal mode (mission mode), CrIS measures the spectral bands from 650 to 1095 cm-1 (long-wave IR band, LWIR), 1210 to 1750 cm-1 (mid-wave IR band, MWIR), and 2155 to 2550 cm-1 (short-wave IR band, SWIR) with spectral resolutions of 0.625 cm-1, 1.25 cm-1 and 2.5 cm-1, respectively. It provides a total of 1305 channels for sounding the atmosphere. CrIS can also be operated in the full spectral resolution (FSR) mode, in which the MWIR and SWIR band interferograms are recorded with the same maximum path difference as the LWIR band. NOAA intends to operate CrIS in FSR mode in the near future. Up to date, the FSR mode has been commanded three times in-orbit (02/23/2012, 03/12/2013, and 08/27/2013). The full resolution SDR data have spectral resolution of 0.625 cm-1 for all three bands (total 2211 channels), and are generated using CrIS Algorithm Development Library (ADL). Quantifying the CrIS radiometric and spectral accuracy is crucial for improving its data assimilation in the numerical weather prediction, and for retrieving atmospheric trace gases. In this study, CrIS full resolution SDR radiometric and spectral accuracy are accessed by using the Community Radiative Transfer Model (CRTM) and European Centre for Medium-Range Weather Forecasts (ECMWF) forecast fields. The biases between observation and simulations are evaluated to estimate the FOV-2-FOV variability and sweep direction bias for clear sky over ocean. Double difference method and Simultaneous Nadir Overpass (SNO) method are also used to assess the CrIS radiance consistency with well-validated IASI. Two basic frequency validation methods (absolute and relative spectral validations) are used to access the CrIS spectral accuracy. Since CrIS SWIR band has much higher resolution than normal mode (2.5 cm-1), it makes possible to use SWIR band to assess the spectral accuracy. All three CrIS bands and 9 field of views (FOVs) are done separately for clear scenes over oceans at nadir (the 15th and 16th field of regards). Results show that CrIS SDRs from FSR have similar radiometric and spectral accuracy as those from normal mode.