Post-launch evaluation and improvements of NOAA-20 VIIRS geolocation accuracy

NOAA-20 (formerly JPSS-1) is a new polar-orbiting weather satellite launched on 18 November 2017. VIIRS is one of five instruments onboard NOAA-20, and it joints on orbit the previous VIIRS instrument operating on the Suomi NPP spacecraft since November 2011. During post-launch testing, accuracy of VIIRS sensor data record (SDR) geolocation products was evaluated using a ground control point matching program. The control points are based on 30-m Landsat images, and the matchups employ their cross-correlation with the 375-m VIIRS images in band I1. Initial NOAA-20 VIIRS geolocation uncertainty after launch exceeded 2 km and was somewhat larger than the initial uncertainty previously observed for S-NPP. Optimization of processing parameters successfully reduced the uncertainty to less than 200 m (3- sigma or CE95), which is comparable to the current geolocation uncertainty for the S-NPP VIIRS SDR products. The improvement was achieved by adjusting only the instrument-to-spacecraft rotation angles (the “mounting matrix”). While the uncertainty evaluation was based on global matchups collected over the entire 16-day orbit repeat period, the optimization was based on reprocessing a two-day set of VIIRS SDR from North Africa and the Middle East. 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 observations of point sources and comparisons between DNB and the I1 band. Initial NOAA-20 VIIRS DNB geolocation uncertainty was even larger than that observed for the other bands, but it was successfully reduced to approximately 200 m by adjusting DNB-specific processing parameters.