Performance Evaluation of On-Orbit Calibration of SNPP VIIRS Reflective Solar Bands via Intersensor Comparison with Aqua MODIS
Abstract
An intersensor comparison is carried out to evaluate the radiometric performance of the reflective solar bands (RSBs) of the first Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-Orbiting Partnership (SNPP) satellite. Two versions of sensor data records (SDRs) for moderate-resolution RSBs M1–M8 (410–1238 nm)—one version from the NOAA Ocean Color (OC) Team and the operational version from the Interface Data Processing Segment (IDPS)—are compared against the well-calibrated Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite. This comparison fully exploits the moderate resolution of the sensors and a precise simultaneous nadir overpass (SNO) analysis in a “nadir only” approach to achieve a precision better than 1%. The key issues found to impact the SNO analysis are 1) an underlying bias beyond the 80-km spatial scale, 2) a scene-based sporadic variability of about 2% affecting the sample size selection criteria, and 3) large relative deviations at low radiances. It is shown that the OC SDRs achieve significantly better agreement with Aqua MODIS, such as smaller temporal variation, improved agreement in the early mission, and no observable long-term drift. The lone exception is the downward drift of about 1% in the Aqua MODIS band 8 (412 nm) versus SNPP VIIRS band M1 time series that possibly started in late 2013, which is ultimately attributed to errors in Aqua MODIS band 8. Finally, the long-term drift in the IDPS SDRs further illustrates the consequence of the worsening bias within the standard RSB calibration that will infect any versions of the VIIRS SDRs not mitigated for this error.
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