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NOAA-20 VIIRS Reflective Solar Bands (RSBs) have been performing well since launch with good quality sensor data records (SDRs). The radiometric performance of these SDRs have been continuously analyzed and monitored using various independent validation techniques. It is important to maintain radiometric consistency between NOAA-20 VIIRS SDRs and other well calibrated instruments such as S-NPP VIIRS for long term environmental applications. Past studies have shown that there exists a near consistent bias in RSBs between the two VIIRS instruments, with NOAA-20 VIIRS top-of-atmosphere (TOA) reflectance being lower by nearly 2-3%. It is crucial to monitor the radiometric consistency between the two VIIRS instruments and help the user community understand the trending of the relative bias between two VIIRS and its impacts on the higher level EDR products. This study is focused on analyzing NOAA-20 VIIRS radiometric bias relative to S-NPP VIIRS operational SDR using different techniques such as the pseudo-invariant calibration sites (PICS) and inter-comparison with other satellite instruments using Simultaneous Nadir Overpasses (SNOs). The impact on bias due to spectral differences between the two VIIRS instruments is quantified using hyperspectral measurements from Sciamachy. Since S-NPP VIIRS is used as a reference, any residual degradation in its operational calibration since 2018 needs to be accounted. The correction for residual degradation will be performed in future for more accurate NOAA-20 VIIRS bias trending once the S-NPP VIIRS reprocessing is completed to the more recent date. The study suggests that NOAA-20 VIIRS reflective solar bands are consistently lower in reflectance than that from S-NPP VIIRS by about 2-3% for most bands. Larger bias is observed for bands M5 (0.67 μm) and M7 (0.86 μm) bands mainly because S-NPP VIIRS absolute calibration for these bands is biased high by about 2%. NOAA-20 VIIRS bias values estimated in this study are consistent with the past studies. The bias remains nearly constant for all the bands. Thus, the study also uses the trend-corrected S-NPP VIIRS data to quantify NOAA-20 VIIRS temporal radiometric bias. Due to shorter span of time for NOAA-20 VIIRS, i.e. ~ two years in orbit, analyzing its radiometric stability using calibration sites is more challenging and results in higher uncertainty. This study uses Libya 4 calibration site to further analyze and validate the radiometric.
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