I. Introduction
The cross-track infrared sounder (CrIS) is a Fourier transform spectrometer (FTS), currently on board the Suomi National Polar-Orbiting Partnership (S-NPP) and NOAA-20 satellites. S-NPP was launched on October 28, 2011, while NOAA-20 was launched on November 18, 2017. The CrIS ground processing software Interface Data Processing Segment (IDPS), part of the Joint Polar Satellite System (JPSS) ground processing system, transforms the measured raw interferograms [raw data records (RDRs)] into calibrated and geolocated spectra in the form of sensor data records (SDRs). The SDRs cover three spectral bands: the long-wave IR (LWIR) band from 650 to 1095 cm−1, mid-wave IR (MWIR) band from 1210 to 1750 cm−1, and short-wave IR (SWIR) band from 2155 to 2550 cm−1 with the nominal spectral resolutions (NSRs) of 0.625, 1.25, and 2.5 cm−1, respectively. CrIS also provides a full spectral resolution (FSR) SDR with a spectral resolution of 0.625 cm−1 for all three bands since December 4, 2014. For an 8-s scan, CrIS sequentially measures 34 interferogram sweeps or fields of regard (FORs) with a 3 3 array of fields of view (FOVs), including 30 earth scene (ES), two deep space (DS), and two internal calibration target (ICT) measurements. Among them, half of the ES, DS, and ICT interferograms are measured in a forward direction and the other half in the reverse direction according to the moving direction of the interferometer porchswing mirror. Radiometric calibrations are separately performed for different sweeping directions, FOVs, and bands using ICT and DS measurements as calibration references.