Improving Suomi NPP CrIS SDR Data Quality to Support Satellite Data Assimilation

Since early 2012, the Cross-track Infrared Sounder (CrIS) on-board the Suomi National Polar-Orbiting Partnership (S-NPP) Satellite has continually provided the hyperspectral infrared observations for profiling atmospheric temperature, moisture and greenhouse gases. CrIS has also been operated in the full spectral resolution (FSR) mode since December 4, 2014. The FSR SDR has more channels in mid-wave and short-wave bands to improve the critical information about atmospheric water vapor and trace gases. The CrIS radiance data are directly assimilated into global NWP models to improve the medium-range forecasts. The CrIS overall performance in spectral, radiometric, geometric calibrations and noise performance in previous studies demonstrated that the CrIS Sensor Data Record (SDR) data meet calibration requirements, thus making it an exceptional asset for weather applications. NWP data assimilation users assume CrIS channels observation error covariance is uncorrelated; the radiance variation among different detectors and sweep directions is less than 0.1 K to effectively apply dynamic bias correction to the radiances; forward simulation can be performed with no knowledge of the CrIS responsivity.

To improve the CrIS data quality and provide the FSR radiance spectra with a spectral resolution of 0.625 cm^-1 for all the three bands, a new calibration algorithm has been developed and implemented for operational uses. The algorithm is an improvement over the previous algorithm that had been operationally used until March 2017. Major changes include the calibration equation, self-apodization correction and resampling matrices, and calibration filter. Compared to the previous algorithm, the improvement reduces the calibration inconsistencies among the nine fields of view and between the forward and reverse interferometer sweep directions by up to 0.5 K, and the differences between observed and simulated spectra by up to 0.4 K by considering the CrIS responsivity in the forward simulation. In this study, the three assumptions will be examined and evaluation results will be presented.