Improving the low light radiance calibration of S-NPP VIIRS day/night band in the NOAA operations

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard Suomi-NPP is equipped with a Day/Night Band (DNB), a major advancement in nighttime imaging capability as compared to the heritage Operational Linescan System (OLS) onboard Defense Meteorological Satellite Program (DMSP). DNB High Gain Stage (HGS) operational radiometric calibration involves estimation of dark offsets using the nighttime measurements over Pacific Ocean during new moon. However, the DNB detectors were found to be highly sensitive, enough to detect faint emission from airglow even during the moonless nights. Thus, the on orbit calculated dark offset is overestimated by an amount equivalent to that of airglow. This causes direct impact in calibrated data such that the radiance values are underestimated in the absolute scale. The impact is prominent at low light radiance. This study focuses on analyzing the airglow using DNB measurements. In addition, the impact on operational calibrated radiance product and how the absolute accuracy can be improved especially at low light radiance are also explored.