VIIRS day/night band (DNB) stray light characterization and correction

Abstract

The Day/Night Band (DNB) on the VIIRS sensor is a panchromatic band that can detect very dim nighttime scenes. After launch of Suomi NPP in October 2011 we observed a gray haze in radiance images with offsets up to 5×10^-9 W cm^-2 sr^-1. Overall this impacts about 25% of nighttime scenes. We considered stray light as the likely cause, and studied calibration data from the space view. We concluded that stray light is likely entering the VIIRS scan cavity directly or indirectly through the nadir door and solar diffuser openings. We also studied the darkest earth scenes without any solar, lunar or artificial illumination, and found that the offset is a function of cross-track pixel, solar angle of incidence (AOI) and detector number. We observed a strong detector dependence causing striping. Dividing scenes into 3 or 4 zones in each hemisphere based on solar AOI, we devised an algorithmic correction based on polynomial fits of the medians of the data for each zone. The correction removed almost all the haze and striping and improved dynamic range by 2 orders-of-magnitude, to as low as 1×10^-10Wcm^-2 sr^-1, but some striping remains in the twilight region due to extrapolation.