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Excellent inter-sensor consistency among these three VIIRS instruments is confirmed through the double-difference analysis method (O-O) using CRTM simulation as a radiance transfer. This method relies on the observation minus background BT differences (O-B ΔBTs), between VIIRS measurements obtained from daily operational data (O) and CRTM simulations (B). The mean inter-VIIRS O-O BT differences remain within 0.08 K for all M-band TEBs, except for M13. Even in the case of M13, the O-O BT differences between NOAA-21 and NOAA-20/S-NPP have values of 0.312 K and 0.236 K, respectively, which are comparable to the 0.2 K difference observed in overlapping TEBs between VIIRS and MODIS at simultaneous nadir overpasses (SNOs). These disparities are primarily attributed to the significant differences in the Spectral Response Function (SRF) of NOAA-21 compared to NOAA-20 and S-NPP.
Our study confirms the effectiveness of the RTM-based TEB quality evaluation method in assessing inter-sensor consistency. The double-difference approach effectively mitigates uncertainties and biases inherent to CRTM simulations, establishing a robust mechanism for assessing inter-sensor consistency. Moreover, it has been noticed that for M12, both the time-series of O-O and O-B BT differences possess the greatest vibrations (i.e., largest standard deviations) compared to other bands, alongside the distinct seasonal variations of O-B BT differences. These observations can be attributed to the fact that M12 radiance is affected by reflected solar radiation during daytime, as M12 operates as a shortwave infrared channel. Furthermore, in this study, we’ve also characterized the spatial distributions of inter-VIIRS BT differences, identifying variations among VIIRS M TEBs.
This paper provides a comprehensive summary of the studies in the postlaunch calibration/validation activities which enables the VIIRS SDR to reach beta, provisional, and calibrated/validation product maturity. The instrument performance is quantified through a large number of tests involving onboard, maneuvers, as well as vicarious calibration/validation. Several issues found in the ground processing are addressed through updating the calibration input parameters known as the lookup tables (LUTs). Instrument performance waivers including the non-standard aggregation mode for the Day/Night band (DNB) and related features are addressed. On-orbit anomalies and mitigations such as the longwave infrared band degradation and saturation in some bands are also discussed. With a local equator crossing time of ~1:30pm with ~50.5 min separation from Suomi NPP achieved since January 2, 2018, NOAA-20 VIIRS provides important Earth observations for generating more than 26 global environmental data records including clouds, sea surface temperature, polar wind, aerosol, vegetation fraction, ocean color, fire, snow and ice for weather, and other environmental applications.
Meanwhile, the calibration of the hyperspectral sounders such as Cross-track Infrared Sounder (CrIS) on NOAA-20 relies on a high quality onboard blackbody which is also traceable to SI through prelaunch characterization relating to the laboratory blackbody with traceable calibration to NIST, and hyperspectral sounders have been recognized as onorbit calibration references for other broad- or narrow-band infrared (IR) observations. In this paper we analyze the traceability of both systems in their raw measurements as well as retrieved geophysical variables. Comparisons are also made in spectral radiance/brightness temperature derived from the two systems. The objective is to gain a better understanding of the different paths of traceability to SI and ensure the consistency of the products for numerical weather prediction and other applications. This study directly supports the COSMIC2 verification and validation, as well as postlaunch calibration/validation of NOAA-20 CrIS.
An improved algorithm for VIIRS Day/Night Band (DNB) high gain stage (HGS) dark offset determination
Trade study of substituting VIIRS M10 with aggregated I3 to enable addition of a water vapor channel
Calibration of low gain radiance at VIIRS emissive band (M13) and VIIRS image about moon temperature
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