Long-term on-orbit performance of the VIIRS on Suomi NPP, NOAA-20, and NOAA-21 in reference to partner missions

Since its successful launch in 2011, the VIIRS (Visible Infrared Imaging Radiometer Suite) on Suomi NPP (Suomi National Polar-orbiting Partnership) has been providing continuous global Earth observations with 22 spectral bands spanning 0.41 to 12.01 μm for over a decade. Originally designed for a 7-year lifespan, Suomi NPP VIIRS has consistently exceeded both its operational specifications and user expectations, successively served as the primary, secondary, and now tertiary satellite imaging radiometer for the NOAA's Joint Polar Satellite System (JPSS) program. Meanwhile, VIIRS on NOAA-20 (launched 2017) and NOAA-21 (launched 2022) have become the secondary and primary imaging radiometers in succession. Building upon lessons learned from SNPP, NOAA-20 VIIRS has distinguished itself as having the most stable reflective solar bands with less than 0.15% responsivity degradation per year in the first 5 years before any correction, and has been endorsed by the World Meteorological Organization/Global Space-based Calibration System (WMO/GSICS) as the on-orbit stability reference. More recently, NOAA-21 VIIRS has become the primary instrument, demonstrating robust performance, especially after the second mid-mission outgassing. This paper evaluates the on-orbit performance of VIIRS instruments, incorporating comprehensive assessments with the calibration methodologies encompassing onboard, vicarious, intercalibration, and recalibration techniques. It focuses on the long-term stability, accuracy, and intersatellite bias assessments using various methods. The root cause for the radiometric biases for the reflective solar bands between Suomi NPP and NOAA-20/-21 is explored, and the recalibration methodology to improve stability and consistency is discussed. Collaborative initiatives with partner satellite programs such as MODIS, the recently launched PACE, EMIT, and the to-be-launched METImage on EPS-SG have also been initiated. These activities underscore the efforts towards achieving consistent, long-term global Earth observations, which are crucial for facilitating time series analyses that support studies on atmosphere, land, ocean dynamics, and artificial nightlight, thereby enhancing global climate change research and operational support for numerical weather predictions.