Vicarious Validation of Suomi-NPP/VIIRS Day /Night Band using DOME-C and Greenland under moon-light

Abstract:

The Day/Night Band (DNB) of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard Suomi-NPP represents a major advancement in night time imaging capabilities. DNB covers almost 7 orders of magnitude in its dynamic range from full sunlight to quarter moon. To achieve this large dynamic range, it uses four charge-coupled device (CCD) arrays in three gain stages. The low gain stage (LGS) gain is calibrated using the solar diffuser. In operations, the medium and high gain stage values are determined by multiplying the gain ratios between the medium gain stage (MGS), and LGS, and high gain stage (HGS) and LGS, respectively. This work focuses on independently verifying the radiometric accuracy and stability of DNB HGS using DNB observation of ground vicarious sites under lunar illumination at night. Dome C in Antarctic and Greenland in northern hemisphere are chosen as the vicarious sites. Nadir observations of these high latitude regions by VIIRS are selected during perpetual night season, i.e. from April to August for Dome C and from Nov. to Jan. for Greenland over the year 2012 to 2013. Additional selection criteria such as lunar phase being more than half moon and no influence of straylight effects are also applied in data selection. Lunar spectral irradiance model, as a function of Sun-Earth-Moon distances and lunar phase, is used to determine the top-of atmosphere (TOA) reflectance at the vicarious site. The vicariously-derived long-term reflectance from DNB observations agrees with the reflectance derived from Hyperion observations. The vicarious trending of DNB radiometric performance using DOME-C and Greenland under moon light shows that the DNB HGS radiometric variability (relative accuracy to lunar irradiance model and Hyperion observation) is within 10%. Residue variability and future work are also discussed.