Ten Years of VIIRS On-Orbit Geolocation Calibration and Performance

Abstract

The first innovative Visible Infrared Imaging Radiometer Suite (VIIRS) sensor aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite has been in operation for 10 years since its launch on 28 October 2011. The second VIIRS sensor aboard the first Join Polar Satellite System (JPSS-1) satellite has been in operation for 4 years since its launch on 18 November 2017, which became NOAA-20. Well-geolocated and radiometrically calibrated Level-1 sensor data records (SDRs) from VIIRS are crucial to numerical weather prediction (NWP) and Level-2+ environmental data record (EDR) algorithms and products. The high quality of Level-2+ EDRs is a requirement for the continuity of NASA Earth science data records (ESDRs) and climate data records (CDRs), one of the two objectives of the SNPP mission and one of the three elements in the JPSS mission objective. The other objective of the SNPP mission is risk reduction for the follow-on JPSS missions. This paper summarizes the on-orbit geolocation calibration and validation (Cal/Val) activities for both VIIRS sensors onboard SNPP and NOAA-20 in the past 10 years. These activities include nominal geolocation Cal/Val activities, risk reduction activities, and improvements for the on-orbit VIIRS sensor operations. After these activities, sub-pixel geolocation accuracy is achieved. Nadir equivalent geolocation uncertainty is generally within 75 m (1-σ), or 20% imagery band pixels, in either the along-scan or along-track direction for both SNPP and NOAA-20 VIIRS sensors. The worst 16-day measured geolocation errors (radial, 3-σ) are 280 m and 267 m, respectively, in the latest SNPP and NOAA-20 VIIRS data collections, which are better than the required accuracy of 375 m (radial, 3-σ). The risk reduction activities also improved VIIRS builds for JPSS-3 and JPSS-4 satellites, and provide lessons learned for other VIIRS-like sensor builds.

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

“…7. The determined optimal parameter value agrees well with that obtained by Lin et al 13 . based on an independent analysis of cross-correlation between VIIRS DNB and Landsat images.…”

“…The third update (in October 2019) added parameters for seamless switching between two “sides” of the scan controller electronics in case it needs to be done on orbit, but it did not change the existing geolocation calculations. In addition to the correction of the VIIRS optical model, 13 the fourth update (in February 2021) included optical model parameter values derived from the pre-launch measurements conducted for N20 VIIRS by the manufacturer. The updated values replaced the SNPP VIIRS ones used previously.…”

“…Although the instrument-to-spacecraft roll/pitch/yaw angles were obtained by the mounting matrix optimization, the HAM alpha/beta/gamma angles, defined in ATBD, 9 are from the measurements acquired during VIIRS pre-launch testing. The table also shows corresponding values obtained at NASA by optimizing all six parameters for processing NASA level 1b products 13 …”

“…The table also shows corresponding values obtained at NASA by optimizing all six parameters for processing NASA level 1b products. 13 In addition to being applied to improve the accuracy of the geolocation products, the angular corrections derived for the 16-day periods were also used to monitor the geolocation errors over timeline of the N20 mission. Figure 5 shows that, following the adjustments of the geolocation processing parameters in 2018, the angular errors display annual oscillations that periodically increase the geolocation errors by up to about 50 m on the ground.…”

“…This approach allowed for timely transition of the VIIRS SDR geolocation products to NOAA operational use within the expected period of three months after the satellite launch. An alternative approach that additionally optimizes the optical model parameters required more time to achieve comparable results for SNPP and N20 12 , 13 …”