An Overview of JPSS-1 CrIS SDR Algorithm and Pre-launch Performance Test Results

The Cross-track Infrared Sounder (CrIS) is a Fourier Transform spectrometer, measuring Earth view interferograms at 30 cross-track positions, each with a 3x3 array of Field-of-Views (FOVs) in the three infrared spectral bands from 650 to 1095 cm-1, 1210 to 1750 cm-1, and 2155 to 2550 cm-1. The first CrIS on the Suomi National Polar-orbiting Partnership Satellite (S-NPP) has been successfully operated since October of 2011. The second CrIS will be on the first Joint-Polar Satellite System (JPSS-1) scheduled to be launched in early 2017. It will be operated in the full spectral resolution (FSR) mode, in which the interferograms of all the three bands are recorded with a maximum optical path difference (MPD) of 0.8 cm. The measured interferograms are processed into calibrated and geolocated spectra at ground by the CrIS Sensor Data Record (SDR) algorithm. The JPSS-1 CrIS SDR algorithm makes significant improvements over the one currently used for the S-NPP CrIS SDR processing. These improvements include: significant reduction of the radiance spectral ringing artifacts; better radiometric consistence among the 9 FOVs; smaller radiometric difference between the interferometer moving mirror's forward and reverse sweep directions in each band. As a result, the bias of the observed and simulated unapodized CrIS spectra is largely reduced. The SDR algorithm has been tested and validated using the measurements from the S-NPP CrIS, which was commanded to the FSR mode on December 4, 2014. The JPSS-1 CrIS pre-launch ground testing work (including the TVAC data collection and analysis) has been successfully completed. These works include: characterization of the instrument noise performance; evaluation of the nonlinearity (NL) for each FOV and determination of the NL correction coefficients; derivation of the Instrument Line Shape parameters for each FOV and the neon metrology wavelength; and establishment of the error budgets for the radiometric, spectral and geolocation calibrations. Overall, the performance of the JPSS-1 CrIS is excellent.