Operational calibration of VIIRS reflective solar band sensor data records

The Visible-Infrared Imaging Radiometer Suite (VIIRS) is an instrument on-board the Suomi National Polar-orbiting Partnership (NPP) spacecraft, which launched on October 28, 2011. VIIRS performs measurements in 14 reflective solar bands (RSBs) spanning wavelengths from 412 nm to 2.25 um, which are calibrated by using solar radiance reflected from a Solar Diffuser (SD). The SD reflectance degrades over time, and a Solar Diffuser Stability Monitor (SDSM) is used to track the changes. The ratio between the calculated solar radiance reflected from the SD and the VIIRS measurement of this radiance using the pre-launch calibration coefficients is known as the “F factor.” The F factor is applied in the ground processing as a scale correction to the pre-launch calibration coefficients used to generate the calibrated radiances and reflectances comprising the Sensor Data Records (SDRs). The F factor is trended over time to track instrument response degradation. The equation for calculating expected solar radiance, and the coefficients used to convert the raw digital numbers measured by the detectors into radiance and reflectance values, are based on parameters stored in various Look-Up Tables (LUTs). This paper will discuss on-orbit RSB calibration for VIIRS, along with a description of the processing methodology, which includes operational LUT updates based on off-line calculations of F factor trending behavior.