Monitoring VIIRS Thermal Emissive Bands Long-Term Performance Using Lunar Observations

Two Visible Infrared Imaging Radiometer Suite (VIIRS) instruments are currently operating in space, one onboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite launched on October 28, 2011 and the other onboard the NOAA-20 satellite launched on November 18, 2017. The performance of the seven VIIRS thermal emissive bands (TEBs) is monitored via on-orbit calibration data, the analysis of Earth view observations, as well as inter-comparisons with other sensors. The Moon has been used as a unique invariant target for on-orbit sensor calibration because its surface property is considered extremely stable over time in spectra, radiometry, and geometry with a repeatable lunar phase. This paper presents the assessments of the S-NPP and NOAA-20 VIIRS TEB on-orbit calibration stability using near-monthly scheduled lunar observations over their respective missions. The methodology previously developed for MODIS is now applied to VIIRS to monitor the TEB long-term stability by extracting and trending the lunar brightness temperatures from selected unsaturated pixels. It includes a correction applied to reduce any impact from the Sun–Moon geometry (e.g. Sun-Moon distance variation). The results show that the mission-long brightness temperature trends from the lunar surface are stable for all VIIRS TEBs, despite noticeable seasonal variations in the lunar thermal emissive radiance.