Inter-Comparing SNPP and NOAA-20 CrIS Toward Measurement Consistency and Climate Data Records

The cross-track infrared sounder (CrIS) is a Fourier transform spectrometer that provides hyperspectral soundings of the atmosphere over three wavelength ranges onboard on both Suomi National Polar-orbiting Partnership (SNPP) and NOAA-20 satellites. Quantifying the radiometric difference and creating a calibration link between SNPP and NOAA-20 CrIS are crucial for creating CrIS long-term climate data records and establishing the space-based calibration standard. This study explores the inter-comparison strategy to identify the radiometric differences between SNPP and NOAA-20 CrIS along the finest spectral scale, including 1) direct comparison; and 2) the two double difference methods using infrared atmospheric sounding interferometer and radiative transfer calculations as transfer targets. Each method has its own advantages and disadvantages. The preliminary results based on the above methods suggest good agreement generally between SNPP and NOAA-20 CrIS. Some consistent findings are disclosed by the above three methods, including 1) around the CO2 absorption band at 650-750 cm
^-1
range, a consistent warm bias is found on the level of 0.1 K; 2) at the water vapor absorption band, the two CrIS instruments are well consistent to each other and their BT differences are close to zero lines albeit with spectral variation; 3) the largest BT difference of more than -0.6 K is found at the spectral line transition region (around 2380 cm
^-1
). The root causes still need further investigation.