Calibration of the VIIRS Day/Night Band (DNB)

Day/Night Band (DNB) on the Visible/Infrared Imager Radiometer Suite (VIIRS) is part of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) and the NPOESS Preparatory Project (NPP). NPOESS is the U.S. next generation weather and climate monitoring system administered by DoD, DOC, and NASA. The DNB on VIIRS is a panchromatic solar reflective band with a dynamic range capable of detecting Earth scenes as dim as quarter moon illumination to the brightest daytime—over 7 orders of magnitude in dynamic range. To achieve this large dynamic range it uses a 3 stage focal plane, where each stage essentially functions as a separate band. The low-gain stage (LGS) is used to observe daytime scenes, the mid-gain stage (MGS) is used to observe dawn or dusk scenes near the Earth's terminator, and the high-gain stage (HGS) is used to observe nighttime scenes with lunar illumination or late twilight. The HGS is also sensitive to city lights, nighttime fires, fishing boats, lightning and the Aurora Borealis.

Calibration of the MGS and HGS is accomplished using the Earth view data in the transition regions between the stages. VIIRS has the capability of transmitting the gain stage data separately or merged, and to perform cross-calibration between the stages, separate data from all 3 must be transmitted. There is a limited region where the low-gain is sensitive but the MGS is not saturated, and the calibration process identifies these regions and than takes the ratios of the data to determinate a relative gain. Likewise, this same process is used to transfer calibration from the MGS to the HGS.