Suomi-NPP VIIRS Recalibration in the Reflective Solar Bands and Day Night Band

The Visible Infrared Imaging Radiometer Suite (VIIRS) was successfully launched on October 28th 2011 on the Suomi-National Polar orbiting Partnership (S-NPP) satellite as a key instrument among other sensors. The VIIRS continues to provide polar orbiting earth observations following the historical sensors such as National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR), National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS), Sea-Viewing Wide Field-of-View Sensor (SeaWiFS), and Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) covering a spectral range from 0.4um to 11.8um in the form of Science Data Records (SDR) and Environment Data Records (EDR). For accurate SDR product generation, the VIIRS uses on-board calibrators that are observed at the end of the Earth View (EV) scans in sequence of Blackbody (BB), Solar Diffuser (SD), Solar Diffuser Stability Monitor (SDSM) and Space View (SV). The primary calibration source of the Reflective Solar Bands (RSB) is the SD. Near the termination point from night to day orbit, the VIIRS makes valid SD observations when the Sun illuminates properly on the SD surface. However there are alternative calibration methods such as lunar and vicarious calibrations, the SD is considered to be the most accurate source of RSB calibration which produces calibration coefficients (so-called F-factors). In this study, the radiometric calibration coefficients, SD based F-factors, are reprocessed within the RSB and day night bands (DNB) from the start of the mission to present. Offline radiometric calibration tools have been developed and implemented in the NOAA ICVS (Integrated Calibration Validation System) for monitoring and long-term validation. The reprocessing of the VIIRS RSB calibration coefficients improved the radiometric accuracy and corrected sudden changes in year 2014. In addition to the RSB calibration coefficient regeneration, the DNB Low Gain State (LGS) gains are reprocessed. Since the DNB LGS gain is linearly proportional the Middle Gain State (MGS) and High Gain State (HGS) gains through the designated gain ratio look-up-tables (LUT), it also affects radiometric accuracy for day and night data products in the DNB band. The reprocessed DNG LGS radiometric gains corrected the sudden radiometric changes caused by Relative Spectral Response (RSR) function update and initial algorithm updates. The reprocessed RSB and DNB calibration coefficients improve and ensure the quality of the early lifetime VIIRS SDR products in year 2012. The details of the calibration trending plots are available at the NOAA ICVS webpage (http://www.star.nesdis.noaa.gov/icvs/status_NPP_VIIRS.php) In the ICVS web page, the reprocessed RSB F-factors and DNB LGS gains are compared with the operational LUTs that are used in the current SDR product generation. The reprocessed radiometric gains are timely monitored by the short and long-term trending charts. These independent off-line calibration coefficients could be used for the entire S-NPP VIIRS reprocessing or product quality monitoring.