Monitoring and Validating VIIRS Level 1b Senor Data Record with Collocated CrIS Measurements

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 M16 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 also has substantial impact on STD, but impact on bias is small. 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.

As uniform and stable objects, the deep convective clouds (DCCs) are often used to monitor the stability of VIIRS Reflective Solar Bands (RSB) and Day-Night-Band (DNB). Usually DCCs are identified by VIIRS 11 µm band brightness temperature (BT), studies show that CrIS has better performance than VIIRS on DCC identification with its stronger and weaker water vapor absorption channels. A BNR (BT difference to noise ratio) method has been developed, and is applied to identify DCCs from collocated CrIS radiance measurements for VIIRS RSB monitoring. This improved DCC detection provides reliable monitoring the stability of RSB bands, which is important for applications.

The methodologies 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).