Post-launch evaluation and improvements of National Oceanic and Atmospheric Administration-20 Visible-Infrared Imaging Radiometer Suite sensor data record geolocation accuracy

Abstract

National Oceanic and Atmospheric Administration (NOAA)-20 (formerly Joint Polar Satellite System-1) is a polar-orbiting weather satellite launched on November 18, 2017. Visible-Infrared Imaging Radiometer Suite (VIIRS) is one of five instruments onboard NOAA-20 (N20), and it jointed on orbit the previous VIIRS instrument operating on the Suomi NPP (SNPP) spacecraft since November 2011. During post-launch testing, the accuracy of VIIRS sensor data record (SDR) geolocation products was evaluated using a system called ground control point matching. The control points are based on 30-m Landsat images as "ground truth," and the matchups employ their cross-correlation with the 375-m VIIRS images in band I1. Initial N20 VIIRS geolocation errors shortly after launch exceeded 2 km and were somewhat larger than those previously observed for SNPP VIIRS. The optimization of processing parameters successfully reduced the geolocation uncertainty to less than 400 m (at nadir, 3-sigma), which is comparable to the current performance for the SNPP VIIRS SDR products, with the majority of the geolocation errors within 200 m. The improvement was achieved by adjusting only the instrument-to-spacecraft rotation angles (the "mounting matrix"). Although the uncertainty evaluation was based on global matchups collected over 12-month periods, the parameter optimization was based on a reduction of the geolocation angular errors by reprocessing VIIRS SDR and re-analyzing the global matchups from 16-day orbit repeat periods. Geolocation of the 750-m day/night band (DNB), which is not co-registered with the 375-m I-bands and the 750-m M-bands, was evaluated and optimized separately, using the correlation between DNB and the I1 band re-projected images. Initial N20 VIIRS DNB geolocation errors were even larger than those observed for the other bands, but they were also successfully reduced by adjusting DNB-specific processing parameters. The initial improvements in the N20 VIIRS geolocation accuracy were achieved in 2018, and the processing parameters were further refined after an optical model correction in 2021.