Determining the DNB dark offset for NASA-provided VIIRS data products

Abstract

Visible Infrared Imaging Radiometer Suite (VIIRS) instruments are currently operating onboard the Suomi-NPP, NOAA-20, and NOAA-21 spacecraft. Two additional instruments are slated to launch as part of JPSS-4 and JPSS-3 in 2027 and 2032, respectively. Unique among the VIIRS bands is the Day-Night Band, which can provide continuous Earth scene measurements throughout a sun-synchronous orbit. This is achieved by leveraging four focal plane arrays, using three different gain settings that provide a dynamic range over seven orders of magnitude. To work in concert, the detector arrays must all be properly calibrated before launch and their performance monitored throughout operation. Key among the DNB calibration parameters is the dark offset, which serves as the background signal level during ground processing. Unlike other VIIRS bands, there is no on-board calibrator to determine the DNB background signal level for its most sensitive gain settings. Monthly calibrations are performed to determine the DNB dark offset during each new moon. We present our methodology for measuring the DNB dark offset using these calibrations along with results from the three operational VIIRS instruments. Also included are comparisons against previously reported methods of determining the DNB dark offset and expected implications for future VIIRS instruments.