S-NPP CrIS Full Spectral Resolution SDR Processing and Quality Assessment

The Cross-track Infrared Sounder (CrIS) on Suomi National Polar-orbiting Partnership Satellite (S-NPP) is a Fourier transform spectrometer. It has been operated in the so-called normal spectral resolution mode since the beginning of the S-NPP mission. In normal mode, CrIS provides a total of 1305 channels over 3 spectral bands from 650 to 1095 cm-1(LWIR), 1210 to 1750 cm-1 (MWIR) and 2155 to 2550 cm-1 (SWIR), with spectral resolutions of 0.625 cm-1, 1.25 cm-1 and 2.5 cm-1, respectively. 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, and therefore the measurements can be processed into spectra with a spectral resolution of 0.625 cm-1 for all three bands (total 2211 channels). NOAA will operate the S-NPP CrIS in FSR mode for the rest of the mission beginning in December 2014. In the first year of FSR operation, NOAA will offline generate the FSR Sensor Data Record (SDR) product from the FSR measurements, while its operational SDR processing system will still produce normal resolution SDRs by truncating the MWIR and SWIR interferograms to the (“normal”) sizes same as those measured in the normal mode operation.

Up to date, the S-NPP has been commanded three times in-orbit into FSR mode (02/23/2012, 03/12/2013, and 08/27/2013) for testing. The CrIS full resolution Processing System (CRPS) has been developed to generate the FSR SDR, which includes the operational CrIS SDR software in the form of Algorithm Development Library (ADL), modified in both algorithm and code to process the FSR data. The FSR SDR software/algorithm was validated based on the Calibration and Validation (Cal/Val) work performed by the CrIS SDR science team on the normal mode data and the assessment of the FSR SDRs generated from the three in-orbit FSR tests. In the assessment work, the radiometric and spectral accuracies were assessed by analyzing the difference between observations and simulations using the Community Radiative Transfer Model (CRTM) and by comparing CrIS with IASI using the Simultaneous Nadir Overpass (SNO) and Double Difference methods. In addition, the consistency in radiometric and spectral accuracy among the 9 Field-of-Views (FOVs) is also evaluated through FOV-to-FOV comparisons. Results showed that CrIS FSR SDRs generated with CRPS have similar radiometric and spectral accuracy as those from normal mode. In this presentation, we will overview the FSR SDR processing algorithms and show the results of the SDR quality assessments from the data collected during the in-orbit FSR tests and the new data that will be received after the S-NPP CrIS is commanded into FSR mode in December 2014.