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.
Highlights
Improvements in Absolute Radiometric Accuracy: While there may be many different definitions of absolute radiometric accuracy, in this paper, we define it as the uncertainty of the Visible Infrared Imaging Radiometer Suite (VIIRS) radiometric measurement relative to the International Systems of Unit (SI) traceable absolute radiometric source, which is typically characterized during prelaunch calibration against a national laboratory standard source and validated on-orbit
Our analyses indicate that the larger M13 bias is mostly due to the coarse spectral resolution of the Cross-track Infrared Sounder (CrIS) SWIR normal spectra data used [19]
This study provides a comprehensive analysis of the recalibration algorithms, proThis study and provides a comprehensive analysis the recalibration algorithms, pro cesses, upgrades, procedures for the recalibration and of reprocessing of the Suomi cesses,sensor upgrades, and procedures for the recalibration reprocessing of processthe Suomi NPP
Summary
Suomi NPP has been operating successfully since its launch on 28 October 2011. VIIRS is one of the major payloads, along with Advanced Technology Microwave Sounder. In the early days of VIIRS operational calibration and data production, there were inconsistencies in both algorithms and calibration inputs, for several reasons. Ocean color, aerosol, and vegetation require time series analysis with several months or years of extremely stable data in order to detect changes or anomalies These types of studies use very sensitive algorithms with historical data and look for subtle changes in the time series or climatology. Calibration stability and accuracy are critical for these types of studies From this perspective, the inconsistencies and artifacts in the operational Suomi NPP VIIRS data significantly impact their use. There is a fundamental need for recalibration To address these issues, we have studied all relevant algorithms and methodologies in satellite calibration, developed a comprehensive algorithm and recalibrated the VIIRS radiometric data that have been recorded since launch. Array-data Stewardship System (CLASS) database [14]
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