Validation of VIIRS with CrIS by taking into account the sub-pixel cloudiness and viewing geometry (Conference Presentation)

The Cross-track Infrared Sounder (CrIS) onboard Suomi NPP (SNPP) and JPSS series has high radiometric accuracy, which can be used for validating some infrared bands of Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the same platform. The collocated CrIS and VIIRS sensor data record (SDR) along with the VIIRS cloud mask product from 19 to 21 September 2016 (during a period of blackbody warm-up cool-down, or WUCD) are used for inter-comparisons. This study addresses the questions on how the sub-pixel cloud presence and the local zenith angle impact the radiometric differences between CrIS and VIIRS. Both VIIRS brightness temperature (BT) bias and standard deviation for I5, M13, M15 and M15 whose spectral response functions (SRFs) have the full coverages over the CrIS spectral regions, are analyzed over the clear and cloudy skies, respectively. Results show good agreement between VIIRS and CrIS, cloud presence has substantial impact on STD, and also impact on BIAS, local zenith angle has also substantial impact on STD, but impact on bias is small. Both bias and STD are large in DCC (deep convective cloud) areas. The study clearly shows the VIIRS scene temperature bias during WUCD, as well as the bias removal after reprocessing the M15 and M16 with the improved calibration bias correction algorithm. The methodology can be applied to monitor and validate the imager with advanced infrared (IR) sounder onboard the same platform, such as CrIS for VIIRS (SNPP, JPSS), IASI for AVHRR (Metop), and GIIRS for AGRI (FengYun-4).