Radiometric evaluation of the SNPP VIIRS reflective solar band sensor data records via inter-sensor comparison with Aqua MODIS

摘要

The Visible Infrared Imaging Radiometer Suite (VIIRS) in the Suomi National Polar-orbiting Partnership (SNPP) satellite has been on orbit for nearly five years since its launch on 28 October 2011. The NOAA Ocean Color (OC) Team through the investigations of Sun and Wang has recently achieved robust calibration of the VIIRS reflective solar bands (RSBs) and generated its own version of the sensor data records (SDRs) with accuracy sufficient for ocean color applications. For the purpose of making a direct evaluation of the SDR performance, for both the OC version and the official Interface Processing Data Segment (IDPS) version, we utilize an inter-sensor radiometric comparison of SNPP VIIRS against the MODerate-resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite for the spectrally matching RSBs. The VIIRS RSBs M1-M8, from 410 to 1238 nm in the spectral range, are tested. Except for the VIIRS M1 versus MODIS Band 8 result, the radiance comparison time series shows that the OC SDRs demonstrate good agreement with Aqua MODIS and overall better results than the IDPS SDRs, such as less variation, no large discrepancy at the beginning of the VIIRS mission, and no long-term drift. The VIIRS M1 versus MODIS Band 8 trend is the lone exception showing a drift in the OC SDR-based trends, but eventually a downward drift of 1% in Aqua MODIS Band 8 is identified to be the cause. It is readily concluded that the inter-comparison result directly demonstrates the OC SDRs to be correct within statistics, especially considering that the ocean color products derived from the OC SDRs have already matured and demonstrated good agreement with in situ data. On the other hand, the IDPS SDR results demonstrably expose the known inherent growing bias in RSB calibration that affects any versions of the SNPP VIIRS SDRs not using the correctly mitigated calibration baseline. The inter-comparison of two moderate-resolution sensors is also an exercise in statistics, and we briefly discuss key points of the pixel-based analysis that establishes the precision and the reliability of the result.