Intercalibration of Successive Sensors in the Same Sun-Synchronous Orbit Utilizing Libya-4

Multiple copies of Reflective Solar Band (RSB) imagers are launched into the same mean local time sun-synchronous orbits to facilitate operational weather forecasting and climate quality retrievals. The successive sensor records need to be intercalibrated to enable consistent cloud and other environmental retrievals. A Pseudo Invariant Calibration Site (PICS), such as Libya-4, can provide radiometric scaling factors between successive sensors without relying on simultaneous nadir overpasses. The clear-sky Libya-4 observed radiances were characterized both spectrally and angularly and were also corrected for atmospheric effects. The Libya-4 natural variability was found to be consistent across the MODIS, VIIRS, and broadband CERES records. The NOAA20 VIIRS and CERES radiances were radiometrically scaled to their SNPP counterparts. This was accomplished by applying the SNPP VIIRS or CERES reflectance characterization models to both the NOAA-20 and SNPP instrument radiances. By comparing the monthly normalized radiance sensor pair relative ratios the sensor pair calibration difference was estimated. The relative monthly ratios also mitigated the Libya-4 surface reflectance and atmospheric variations. The methodology enables future VIIRS or CERES instruments to be scaled against concurrent NOAA instruments within a few months after launch.