Preliminary Study of JPSS-1/NOAA-20 VIIRS Day-Night Band Straylight Characterization and Correction Methods

The JPSS-1 (now named NOAA-20) VIIRS instrument has successfully operated since its launch in November 18, 2017. A panchromatic channel onboard NOAA-20 VIIRS is called the day-night band (DNB). With its large dynamic range and high sensitivity, the DNB detectors can make observations during both daytime and nighttime. However, the DNB night image quality is affected by the straylight contamination. In this study, we focused on Earth view data in the midto-high latitude of the northern and southern hemispheres when spacecraft is crossing the day/night terminators at the beginning of NOAA-20 mission. Based on on-orbit data analysis from previous VIIRS sensor onboard S-NPP mission, straylight contamination mainly depends on the Earth-Sun-spacecraft geometry, and it is also detector and scan-angle dependent. Inter-comparison investigation of straylight behavior in both SNPP and NOAA-20 instruments will be conducted to better understand straylight characteristics. The preliminary study has been performed in this paper to mitigate straylight contamination for NOAA-20VIIRS DNB night images. The effectiveness of the straylight correction algorithm, directly adapted from the S-NPP DNB, is assessed for night images in the day/night terminators. Further work has been identified to improve current straylight correction methodology and DNB-based environmental data products.NOAA-20

Performance Assessment of S-NPP VIIRS Solar Diffuser and Lunar Calibration

The S-NPP VIIRS has successfully operated on-orbit since its launch in October, 2011. It has 22 spectral bands: 14 reflective solar bands (RSB), 7 thermal emissive bands (TEB), and 1 day night band (DNB). The VIIRS RSB calibration is performed each orbit by the on-board solar diffuse (SD). The SD on-orbit degradation is currently tracked on a daily basis by an on-board solar diffuser stability monitor (SDSM). In addition, near-monthly lunar observations have been scheduled and implemented to independently track the RSB calibration stability. Early on-orbit observations revealed that the VIIRS rotating telescope assembly (RTA) mirrors had experienced strong wavelength dependent degradation, especially in the NIR and SWIR spectral region. Because of this, the sensor’s relative spectral response (RSR) needs to be revised and updated. It is expected that the modulated RSR due to wavelength dependent mirror degradation will have different impact on the SD and lunar calibration. This paper identifies some of the key factors that need to be considered in VIIRS SD and lunar calibration algorithms. It discusses their impact on RSB calibration and mitigation strategies developed to maintain sensor calibration quality and to generate consistent sensor data records (SDR)