Update on the Performance of Suomi-NPP VIIRS Lunar Calibration

Lunar observations have been regularly scheduled for the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite since its launch on October 28th, 2011. In reference to the ROLO irradiance model, the detector gain coefficient (F-factor) can be derived from these lunar observations for the reflective solar bands (RSB). Unlike its predecessor Moderate Resolution Imaging Spectro-radiometer (MODIS), the Moon and the on-board solar diffuser (SD) are viewed by VIIRS detectors at the same angle of incidence (AOI) to the half angle mirror (HAM). This design eliminates the impact of the variation in the instrument response to the HAM AOI and allows the detector gain changes tracked by the Moon and the SD directly comparable. In this paper, we update the results of scheduled lunar calibration. The long-term trends of F-factors calibrated by the Moon and by the SD still agree within +/-1% for all RSBs. We also calculate the lunar F-factor at detector level and compare the detector dependency of the lunar F-factor and the SD F-factor. For a few bands, deviation of up to 1% between the two has been identified. The deviation indicates another unspecified systematic bias between the lunar and SD calibration approaches. Applying detector dependency based on lunar calibration may reduce the striping observed in the Earth view product derived using SD F-factor.