Suomi NPP Day/Night Band (DNB) low light radiometry and long term radiometric characteristics

The Day/Night Band (DNB), part of the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor, was launched aboard the Suomi NPP on 28 October 2011. The DNB covers almost 7 orders of magnitude in its dynamic range from full sunlit scenes to lunar illuminated clouds. The DNB is panchromatic and covers the wavelengths from 500 nm to 900 nm. While DNB has a minimum radiance requirement of 3x10-9 W∙cm-2∙sr-1, we have found that in near-nadir aggregation zones, it is capable of producing useful imagery at a radiance level at least an order of magnitude dimmer at 3x10-10 W∙cm-2∙sr-1 which is approximately equal to the signal expected from airglow. Therefore, in order to use this data quantitatively, one must remove the airglow contamination in the offset determination of the DNB calibration process. In this paper, we will discuss the use of photon transfer curve to extract low light signal in the presence of an unknown offset from the DNB data and how this can be applied to the DNB data to derive the true offset for DNB calibration. We will also discuss the long term trend in DNB SNR, noise characteristics and offset stability which can all be determined with the photon transfer curve technique.