Persistent bias in the Level-1B Top-of-Atmosphere Reflective Solar Band values between S-NPP VIIRS and JPSS-1 (NOAA20) VIIRS
|Last Updated||2021-02-01 21:10:00|
The VIIRS instrument aboard both the Suomi NPP (S-NPP) and the JPSS-1 (NOAA20) platforms were launched in October 2011 and November 2017, respectively. Since their launches, the Reflective Solar Bands (RSB), in both cases, have been performing well with good quality Top-of-Atmosphere (TOA) data. A handful of different groups have studied the data from both instruments and have documented a persistent bias between their Level-1B (L1B) TOA RSB values. This bias has a spectral dependency and ranges between ~2% - 6% for most RSBs. In most cases, the S-NPP VIIRS TOA radiance was apparently brighter (higher) than its JPSS-1 VIIRS counterpart. Currently, we don't know what causes such a bias, and surmise that it is most likely caused by some differences and/or flaws in the S-NPP's sensor characteristics. Persistent radiometric consistency between the two instruments is essential if we are to avoid any impact of such relative bias on downstream L2/L3 products, and also when we seek to combine observations from both instruments.
Please do note that the Thermal Emissive Bands (TEB) behavior is more closely aligned between the two VIIRS instruments, and we have not found any significant bias among the TEBs.
The VIIRS Calibration Support Team and the Land Science Team have investigated this issue. The NASA discipline teams and NOAA STAR teams have also studied it, and reached similar conclusions. You can access these studies and presentations via LDOPE's description documenting this issue: