Updates to the on-orbit calibration of SNPP VIIRS for ocean color applications

Abstract

The NASA Ocean Biology Processing Group (OBPG) has continued monitoring the SNPP VIIRS on-orbit calibration since the derivation of the calibration for Reprocessing 2014.0 of the VIIRS ocean color data set. That calibration was based on solar and lunar observations through July 2014. Updates to the R2014.0 calibration include: 1) the addition of solar and lunar observations through May 2015; 2) the extension of the lunar libration corrections to incorporate sub-solar point corrections in addition to sub-spacecraft point corrections; 3) the implementation of a shortwave infrared (SWIR) band lunar and solar calibration; and 4) the absolute calibration of the solar observations using solar diffuser measurements. The SWIR band lunar calibration shows residual libration effects. Comparison of the lunar and solar time series yields lunar-derived adjustments to the solar calibration. The solar calibration time series show RMS residuals per band of 0.066–0.17%. The lunar calibration time series show RMS residuals per band of 0.072–0.23%. The solar and lunar time series show RMS differences per band of 0.10–0.23%. The VIIRS on-orbit calibration stability is comparable to that achieved for heritage instruments (SeaWiFS, Aqua MODIS). The quality of the resulting ocean color products is sufficient for incorporation of the VIIRS data into the long-term NASA ocean color data record.