Mission-Long Recalibrated Science Quality Suomi NPP VIIRS Radiometric Dataset Using Advanced Algorithms for Time Series Studies

Abstract

Suomi NPP has been successfully operating since its launch on 28 October 2011. As one of the major payloads, along with microwave and infrared sounders (Advanced Technology Microwave Sounder (ATMS), Cross-track Infrared Sounder (CrIS)), and ozone mapping/profiling (OMPS) instruments, the Visible Infrared Imaging Radiometer Suite (VIIRS) has performed for well beyond its mission design life. Its data have been used for a variety of applications for nearly 30 environmental data products, including global imagery twice daily with 375 and 750 m resolutions, clouds, aerosol, cryosphere, ocean color and sea-surface temperature, a number of land products (vegetation, land-cover, fire and others), and geophysical and social economic studies with nightlights. During the early days of VIIRS operational calibration and data production, there were inconsistencies in both algorithms and calibration inputs, for several reasons. While these inconsistencies have less impact on nowcasting and near real-time applications, they introduce challenges for time series analysis due to calibration artifacts. To address this issue, we developed a comprehensive algorithm, and recalibrated and reprocessed the Suomi NPP VIIRS radiometric data that have been produced since the launch. In the recalibration, we resolved inconsistencies in the processing algorithms, terrain correction, straylight correction, and anomalies in the thermal bands. To improve the stability of the reflective solar bands, we developed a Kalman filtering model to incorporate onboard solar, lunar, desert site, inter-satellite calibration, and a deep convective cloud calibration methodology. We further developed and implemented the Solar Diffuser Surface Roughness Rayleigh Scattering model to account for the sensor responsivity degradation in the near infrared bands. The recalibrated dataset was validated using vicarious sites and alternative methods, and compared with independent processing from other organizations. The recalibrated radiometric dataset (namely, the level 1b or sensor data records) also incorporates a bias correction for the reflective solar bands, which not only addresses known calibration biases, but also allows alternative calibrations to be applied if so desired. The recalibrated data have been proven to be of high quality, with much improved stability (better than 0.3%) and accuracy (by up to 2%). The recalibrated radiance data are now available from 2012 to 2020 for users and will eventually be archived on the NOAA CLASS database.

SNPP VIIRS Day Night Band: Ten Years of On-Orbit Calibration and Performance

“…About 42% degradation is observed at wavelength 0.412 µm so far. At this point in the on-orbit operations, the largest degradation is confirmed as being at the shortest wavelength [11][12][13][14][15][16][17][18]. In this figure, a coverage of the Figure 2 shows the VIIRS SD degradation as measured by the solar diffuser stability monitor (SDSM) [1,[11][12][13] at five times during the mission: orbits of 2000, 5000, 15000, 35000 and 50000, which correspond to 17 March 2012, 14 October 2012, 19 September 2014, 30 July 2018, and 22 June 2021, respectively.…”

“…About 42% degradation is observed at wavelength 0.412 µm so far. At this point in the on-orbit operations, the largest degradation is confirmed as being at the shortest wavelength [11][12][13][14][15][16][17][18]. In this figure, a coverage of the DNB wavelength is plotted background in green dots.…”

“…The same principles are used in both NASA VCST and NOAA IDPS for developing the DNB stray light estimation algorithm [7,8,[14][15][16][17]. During a new moon, signals observed over the dark Earth scene are the result of a combination of stray light and airglow.…”

“…The second difference is that the VCST calculates the dark scene signals via smoothing over the spacecraft zenith and scan angles. However, the IDPS directly averages the dark scene signals [9,16,17]. In practice, the VCST uses neighbor correlation effects to decrease estimation uncertainty on dark scene signals.…”

An Approach for Evaluating Multisite Radiometry Calibration of Sentinel-2B/MSI Using RadCalNet Sites

“…For each spectral band, the equivalent TOA reflectance was calculated with a known surface reflectance and a known atmosphere, and the ratio between the observed and the simulated equivalent TOA reflectance was derived. However, due to the surface-atmosphere coupled effect, the calibration results and associated uncertainties for each sample were inconsistencies for several reasons, and these inconsistencies would introduce challenges for time series analysis due to calibration artifacts [5]. Thus, the challenge is to reconcile these independent results and provide a comprehensive estimate.…”