Intercomparison Between VIIRS and CrIS by Taking Into Account the CrIS Subpixel Cloudiness and Viewing Geometry

Abstract

The Cross-track Infrared Sounder (CrIS) onboard the Suomi National Polar-orbiting Partnership (SNPP) has high radiometric accuracy, which can be used to intercompare and understand the radiometric performance of the thermal emissive bands of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the same platform. Previous studies usually selected uniform scenes to avoid potential uncertainties due to geolocation errors. This study focuses on all scenes (including nonuniform scenes), as well as CrIS subpixel cloudiness, local zenith angle and surface type, and their impacts on VIIRS/CrIS intercomparisons. A geolocation error correction scheme is applied to mitigate the geolocation mismatch between CrIS and VIIRS. Intercomparison results of three days from 19 to 21 September 2016, a quarterly warm up/cool down calibration period, show overall good agreement in terms of radiance biases (less than 0.2 K in terms of brightness temperature) between VIIRS and CrIS, for scene temperatures between 220 and 300 K; however, larger biases are evident outside of this range. The three factors—CrIS subpixel cloudiness, local zenith angle, and surface type—show weak impacts on VIIRS radiance biases. Both clear-sky and overcast conditions have slightly different radiance biases from other partially cloudy conditions because of more contributions from colder or warmer scenes. The time series show the impact of warm up/cool down and the effectiveness of the correction algorithm for reprocessing VIIRS M15 and M16 data sets. The methods and tools can be applied to monitor and validate other infrared imager/sounder duos onboard the same platform.