A New Method for Suomi-NPP VIIRS Day-Night Band On-Orbit Radiometric Calibration

The Suomi National Polar-orbiting Partnership Visible Infrared Imaging Radiometer Suite (S-NPP VIIRS) instrument contains a visible imaging band designed to produce imagery during both daytime and nighttime, which is called the day-night band (DNB). The DNB is a three-gain-stage backside-illuminated charge-coupled device (CCD) with four detector arrays that aggregate the individual CCD pixels into 32 different aggregationmodes across scan, yielding imagery with a roughly constant horizontal sampling interval. The highest gain stage is over 100 000 times more sensitive than the lowest gain stage; the combination of the three gain stages allows for imagery with radiances ranging from 10(-10) to 10(-2) W . cm(-2) . sr(-1). The initial DNB on-orbit calibration relies onmonthly sensor special operations. This offline calibration approach results in discrete calibration and the loss of some science data. In this paper, we will present a new calibration method based solely on VIIRS onboard calibrators (OBCs). The calibrator data collected on the nighttime side of an orbit are used to determine the dark offset and the data collected over the daytime side of the orbit, and the day-night terminators are used to compute the cross-stage gain ratios. The results showed that the dark offset and the gain ratio derived from the initial method could be biased up to ten digital numbers (DN) and 12%, respectively, due to nighttime airglow and Earth scene stray light. The calibration is also continuous as calibrator data are recorded for each scan. Because no special operation and offline analysis are required, this method was approved for VIIRS operational implementation to improve the DNB radiometric calibration and sensor on-orbit operations.