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The Visible-Infrared Imaging Radiometer Suite (VIIRS) is a primary sensor on-board the Suomi-National Polar-orbiting Partnership (S-NPP) and National Oceanic and Atmospheric Administration 20 (NOAA-20) spacecrafts, launched in October 2011 and November 2017, respectively. VIIRS has 22 bands: 7 thermal emissive bands (TEBs), 14 reflective solar bands (RSBs) and a Day Night Band (DNB). Both the RSBs and TEBs use a combination of pre-launch and on-orbit calibration information to provide accurate radiance, reflectance, and brightness temperature Sensor Data Records (SDRs). An on-orbit comparison of the S-NPP and NOAA-20 RSB SDR radiances, using ground calibration sites and vicarious methods such as deep convective clouds, show that there is a ~2% bias between the two sensors for all the reflective solar bands. Additionally, the M5 (0.672 μm) and M7 (0.865 μm) bands of Suomi NPP VIIRS have larger biases. An investigation of each sensor’s pre-launch and on-orbit calibrations was performed to ascertain the root cause of the sensor-to-sensor bias. This paper will discuss the VIIRS methodologies for both pre-launch and on-orbit calibration and how they affect the SDR product performance, as well as the most likely cause for the bias . In particular, the characterization of the reflectance of the Solar Diffuser and its reflectance variation versus view geometry was performed with different methodologies for S-NPP and NOAA-20 VIIRS. It is anticipated that J2, J3 and J4 VIIRS sensors will behave more similarly to NOAA-20 than S-NPP VIIRS due to the methodology for the SD characterization being consistent with NOAA-20.
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