Hyper-spectral Infrared Sensor CrIS Sensor Data Record Long-term Radiometric and Spectral Accuracy and Stability

The Cross-track Infrared Sounder (CrIS) on the Suomi NPP (SNPP) is a high spectral resolution Fourier Transform Spectrometer (FTS). Since successfully launched on 28 October 2011, there are more than 4 years operational Sensor Data Records (SDRs) generated by the NOAA operational processing software Interface Data Processing Segment (IDPS). These SDR data are available for improving weather forecasting by providing high vertical resolution of temperature and water vapor profiles, and for climate applications by providing high accuracy, high stability, and extensive information about trace gases, cloud properties, and surface properties. Quantifying the CrIS radiometric and spectral accuracy and long-term stability is crucial for improving its data assimilation in the numerical weather prediction, and for climate application to detect climate trend. In this study, CrIS SDR (including operation IDPS SDRs and full spectral resolution SDRs generated by NOAA/STAR) radiometric accuracy and stability are assessed 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 and the FOV-2-FOV variability is also assessed for clear sky over ocean. Two basic spectral calibration methods are used to assess the CrIS SDR spectral accuracy: 1). Relative spectral calibration, which uses two uniform observations to determine frequency offsets relative to each other; 2). Absolute spectral calibration, which requires an accurate forward model to simulate the top of atmosphere radiance under clear conditions and correlates the simulation with the observed radiance to find the maximum correlation. We use LBLRTM and ECMWF forecast fields to systematically evaluate the spectral accuracy of CrIS SDR at different spectral ranges for all three bands. Based on these results, the best spectral ranges can be chosen to evaluate the spectral accuracy and stability for CrIS, IASI and future FTS infrared instruments. Long-term CrIS radiometric and spectral accuracy and stability from the operational CrIS SDR will be presented in this study.