RSB calibration of SNPP VIIRS using solar diffuser illuminated by scattered light

We present a new variant to the on-orbit calibration methodology for the reflective solar bands (RSBs) of SNPP VIIRS using solar diffuser (SD). Instead of following the standard method using full solar illumination through SD port that occurs during terminator crossing, we use light scattered off Earth scenes coming through the nadir port as the source of illumination for the SD. We describe the methodology, present the result, and compare with standard result. The scattered light signal for each orbit is summed up and a 16-day average is taken to build up the calibration coefficient trend. The preliminary result for SNPP VIIRS Bands M1 through M7 shows the scatter light-based approach to be viable, with its calibration coefficient result very well match the standard RSB calibration result over the entire mission to date. The preliminary result does show more variation, on the level of 2%. The methodology is applicable to other instruments employing a similar SD-based calibration strategy. Specifically for the twin MODIS in which the on-orbit RSB calibration is effectively identical, this approach is directly applicable as is.