Abstract
The S-NPP VIIRS instrument has successfully operated for more than 3 years since its launch in October, 2011. It has 15 reflective solar bands (RSB) and 7 thermal emissive bands (TEB). The VIIRS RSB include a day night band (DNB), covering wavelengths from 0.41 to 2.3 um. The VIIRS instrument and its on-board calibrators were built with strong MODIS heritage. Its RSB calibration is reflectance-based via an on-board solar diffuser (SD). The SD BRDF was characterized pre-launch and its on-orbit changes are tracked by an on-board solar diffuser stability monitor (SDSM), which has 8 filtered detectors covering wavelengths from 0.41 to 0.93 um. A fixed solar attenuation screen, placed in front of the SD panel, is part of the SD/SDSM calibration system. The VIIRS SD measurements are made every orbit, whereas the SDSM measurements are made at pre-determined frequencies. Like MODIS, the VIIRS also makes lunar observations through its space view port to monitor its RSB on-orbit calibration stability. This paper provides an overview of VIIRS RSB on-orbit solar and lunar calibration methodologies and an update of its on-orbit performance based on the SD and lunar calibrations performed over last three years. It describes various improvements and calibration impact assessments made in response to various issues identified since launch, including uncertainties in SD degradation, SD and SDSM screen transmission, sensor modulated relative spectral response (RSR), and reference lunar spectral irradiance.
Status of S-NPP VIIRS Solar and Lunar Calibration
The S-NPP VIIRS instrument has successfully operated for more than 3 years since its launch in October, 2011. It has 15 reflective solar bands (RSB) and 7 thermal emissive bands (TEB). The VIIRS RSB include a day night band (DNB), covering wavelengths from 0.41 to 2.3 um. The VIIRS instrument and its on-board calibrators were built with strong MODIS heritage. Its RSB calibration is reflectance-based via an on-board solar diffuser (SD). The SD BRDF was characterized pre-launch and its on-orbit changes are tracked by an on-board solar diffuser stability monitor (SDSM), which has 8 filtered detectors covering wavelengths from 0.41 to 0.93 um. A fixed solar attenuation screen, placed in front of the SD panel, is part of the SD/SDSM calibration system. The VIIRS SD measurements are made every orbit, whereas the SDSM measurements are made at pre-determined frequencies. Like MODIS, the VIIRS also makes lunar observations through its space view port to monitor its RSB on-orbit calibration stability. This paper provides an overview of VIIRS RSB on-orbit solar and lunar calibration methodologies and an update of its on-orbit performance based on the SD and lunar calibrations performed over last three years. It describes various improvements and calibration impact assessments made in response to various issues identified since launch, including uncertainties in SD degradation, SD and SDSM screen transmission, sensor modulated relative spectral response (RSR), and reference lunar spectral irradiance.