Abstract
The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on-board the Suomi-NPP satellite has successfully operated for more than 2 years since its launch in October, 2011. VIIRS has 15 reflective solar bands (RSB) with wavelengths ranging from 0.41 to 2.3 um, which include a day night band (DNB). VIIRS RSB calibration is performed each orbit using an on-board solar diffuser (SD). A fixed solar attenuation screen is placed in front of the SD panel. The SD on-orbit degradation is tracked on a daily basis by a solar diffuser stability monitor (SDSM), which has 8 filtered detectors covering wavelengths from 0.41 to 0.93 um. On a regular basis, VIIRS also makes lunar observations through its space view port, enabling an independent evaluation of its RSB calibration stability. For this purpose, the lunar observations are scheduled at the “same” phase angles. This paper provides an overview of VIIRS RSB on-orbit calibration methodologies. It examines the RSB response trending derived from both SD and lunar observations made over last two years, identifies various issues that need to be addressed for further improvements. Specifically, it will discuss the calibration impact due to uncertainties in SD degradation, screen transmission, sensor modulated relative spectral response (RSR), and reference lunar spectral irradiance.
Improvements of VIIRS Reflective Solar Bands (RSB) Solar and Lunar Calibration
The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on-board the Suomi-NPP satellite has successfully operated for more than 2 years since its launch in October, 2011. VIIRS has 15 reflective solar bands (RSB) with wavelengths ranging from 0.41 to 2.3 um, which include a day night band (DNB). VIIRS RSB calibration is performed each orbit using an on-board solar diffuser (SD). A fixed solar attenuation screen is placed in front of the SD panel. The SD on-orbit degradation is tracked on a daily basis by a solar diffuser stability monitor (SDSM), which has 8 filtered detectors covering wavelengths from 0.41 to 0.93 um. On a regular basis, VIIRS also makes lunar observations through its space view port, enabling an independent evaluation of its RSB calibration stability. For this purpose, the lunar observations are scheduled at the “same” phase angles. This paper provides an overview of VIIRS RSB on-orbit calibration methodologies. It examines the RSB response trending derived from both SD and lunar observations made over last two years, identifies various issues that need to be addressed for further improvements. Specifically, it will discuss the calibration impact due to uncertainties in SD degradation, screen transmission, sensor modulated relative spectral response (RSR), and reference lunar spectral irradiance.