NOAA-20 VIIRS DNB Aggregation Mode Change: Prelaunch Efforts and On-Orbit Verification/Validation Results

Abstract

The Visible Infrared Imaging Radiometer Suite (VIIRS) on-board the National Oceanic and Atmospheric Administration-20 (NOAA-20, previously named Joint Polar Satellite System-1 or J1) satellite was successfully launched in late 2017, following six years of a successful operation by its predecessor on the Suomi National Polar-Orbiting Partnership (S-NPP) satellite. NOAA-20 VIIRS day/night band (DNB) adopts a new on-board aggregation option (Op21), which is different from S-NPP DNB (using Op32), to mitigate high non-linearity at high scan angles, observed in its radiometric response during prelaunch test. As a result, NOAA-20 VIIRS DNB has a larger scan angle at the end of scan (~60.5°) and exhibits a unique feature, i.e., ~600 km extended Earth view (EV) samples, compared to S-NPP DNB and other VIIRS bands. VIIRS geolocation (GEO) algorithm and geometric calibration parameters were analyzed in-depth and subsequently modified to accommodate the NOAA-20 VIIRS DNB aggregation mode change. The GEO code change was tested using S-NPP data; S-NPP DNB simulated J1 DNB radiance and limited J1 prelaunch test data. After the launch, it was further verified using NOAA-20 VIIRS on-orbit observations. Our results show that the prelaunch VIIRS GEO code change performs well. GEO validation results using nighttime point sources show that NOAA-20 DNB GEO errors are comparable to those for S-NPP DNB over the nominal EV range, with averaged nadir equivalent GEO errors less than 200 m after on-bit updates. Over the extended EV samples (scan angle > 56.06°), the averaged GEO errors are less than 500 m. Moreover, NOAA-20 VIIRS DNB radiometric calibration performance is comparable to S-NPP.