Assessment of CrIS Geolocation Accuracy using VIIRS

The Cross-track Infrared Sounder (CrIS) on the newly-launched Suomi National Polar-orbiting Partnership (Suomi NPP) and future Joint Polar Satellite System (JPSS) is a Fourier transform spectrometer that provides soundings of the atmosphere with 1305 spectral channels, over 3 wavelength ranges: LWIR (9.14 - 15.38 μm); MWIR (5.71 - 8.26 μm); and SWIR (3.92 - 4.64 μm). An accurate spectral and radiometric calibration as well as accurate geolocation is fundamental for CrIS radiance Sensor Data Records (SDRs). Given a 14-km CrIS field-of-view (FOV) at nadir, the designed specification of CrIS Geolocation is less than 1.5km, which is on the order of tenth of CrIS FOV size.

In order to evaluate CrIS geolocation at a sub-pixel level, a method is developed by using the collocated radiance measurements from Visible Infrared Imaging Radiometer Suite (VIIRS) infrared bands. Specifically, an algorithm has been developed to accurately determine the footprint shapes of CrIS FOVs. The VIIRS pixels are then spatially averaged to compare with CrIS measurements, which are convolved with VIIRS spectral response function to generate VIIRS band radiances. By shifting the VIIRS pixel toward along- and cross-track direction, the perfect collocation position can be indentified to quantify the geolocation bias of CrIS geolocation FOVs. The poster overviews the method, summarizes the first year of geolocation analysis, and provides the assessment results on CrIS geolocation. More important, the proposed approach allows an operational, long-term characterization of the CrIS geolocation and enables individual CrIS observations to be geolocated to the sub-pixel accuracy that is required for CrIS data application.