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Aboard the polar-orbiting SNPP satellite, the VIIRS instrument has been in operation since launch in October 2011. It is a visible and infrared radiometer with a unique panchromatic channel capability designated as a day-night band (DNB). This channel covers wavelengths from 0.5 to 0.9 µm and is designed with a near-constant spatial resolution for Earth observations 24 h a day. The DNB operates at 3 gain stages (low, middle, and high) to cover a large dynamic range. An onboard solar diffuser (SD) is used for calibration in the low gain stage, and to enable the derivation of gain ratios between the different stages. In this paper, we present the SNPP VIIRS DNB calibration performed by the NASA VIIRS characterization support team (VCST). The DNB calibration algorithms are described to generate the calibration coefficient look up tables (LUTs) for the latest NASA Level 1B Collection 2 products. We provide an evaluation of DNB on-orbit calibration performance. This activity supports the NASA Earth science community by delivering consistent VIIRS sensor data products via the Land Science Investigator-led Processing Systems, including the SD degradation applied for DNB calibrations in detector gain and gain ratio trending. The DNB stray light contamination and its correction are highlighted. Performance validations are presented using comparisons to the calibration methods employed by NOAA’s operational Interface Data Processing Segment. Further work on stray light corrections is also discussed.

The MODIS imaging spectroradiometer instruments on-board NASA's Terra and Aqua satellites have 20 reflective solar bands (RSB) covering a wavelength range from 400 to 2200 nm. Radiance is calculated from processing raw signals with background, temperature, and electronic contamination corrected. Measured gain is calibrated with a fully Sunlit solar diffuser (SD) at a stable radiance level, considering a slowly changing SD reflectance degradation. These measurements provide time-dependent gain adjustment factors, and the calibration assumes a linear response for each band and detector. Hence, an analysis of the dependence on different radiance levels is warranted. The MODIS design has no mechanism for varying radiance levels, except for an attenuator screen. However, it has been in static configuration for Terra since mid-2003. An external source of radiance attenuation can be utilized during solar eclipse events, while maintaining high stability and accuracy of solar calibration standards. Due to its long mission lifetime, Terra has seen several Sun-Moon near-conjunction events when it coincides with the orbit path where the SD is directly illuminated. As of August 2020, we have identified 7 viable partial solar eclipses in the Terra mission data. We will discuss several results of our study, including comparison of measured SD signal to predicted radiance reduction based on a solar disk radiance model; nominal and outlier behavior as a function of bands, detectors, and mirror-sides; and comparison with other data sets. Our main conclusion from this study is that there is no notable correlation of detector-dependent trend with radiance level for most RSB bands.