Abstract
The VIIRS (Visible-Infrared Imaging Radiometer Suite) instrument onboard the Suomi NPP (National Polar-orbiting Partnership) spacecraft started acquiring Earth observations in November 2011. Since then, radiometric calibration applied to the VIIRS RSB (Reflective Solar Band) measurements for the SDR (Sensor Data Record) production has been improved several times. Initially, radiometric calibration coefficients were updated once per week to correct for the responsivity degradation that occurs for some of the sensor’s spectral bands due to a pre-launch contamination of the VIIRS telescope’s mirrors. In August 2012, magnitude of the radiometric coefficient changes between the updates was greatly reduced by implementing a procedure that predicts (about a week ahead) values of the calibration coefficients for each Earth scan until a subsequent update. The updates have been continued with the weekly frequency, and coefficient prediction errors were monitored. The weekly predicted coefficients have been compared with the coefficients derived once per orbit from the onboard solar diffuser measurements by an automated procedure, called RSBAutoCal, scheduled for implementation in the VIIRS SDR operational processing in 2014. The presentation evaluates the changes in the VIIRS RSB coefficient updates and their potential impacts on application of the remote sensing measurements in the visible (Vis), near-infrared (NIR), and short-wave infrared (SWIR) bands throughout the two-year period of the Suomi NPP mission. Preliminary comparisons between the calibration coefficients generated by the RSBAutoCal and the current operational versions are also presented, as is the dependence of the radiometric calibration on processing coefficients such as attenuation screen transmittance and solar diffuser bidirectional reflectance.
VIIRS Reflective Solar Bands Calibration Changes and Potential Impacts on Applications
The VIIRS (Visible-Infrared Imaging Radiometer Suite) instrument onboard the Suomi NPP (National Polar-orbiting Partnership) spacecraft started acquiring Earth observations in November 2011. Since then, radiometric calibration applied to the VIIRS RSB (Reflective Solar Band) measurements for the SDR (Sensor Data Record) production has been improved several times. Initially, radiometric calibration coefficients were updated once per week to correct for the responsivity degradation that occurs for some of the sensor’s spectral bands due to a pre-launch contamination of the VIIRS telescope’s mirrors. In August 2012, magnitude of the radiometric coefficient changes between the updates was greatly reduced by implementing a procedure that predicts (about a week ahead) values of the calibration coefficients for each Earth scan until a subsequent update. The updates have been continued with the weekly frequency, and coefficient prediction errors were monitored. The weekly predicted coefficients have been compared with the coefficients derived once per orbit from the onboard solar diffuser measurements by an automated procedure, called RSBAutoCal, scheduled for implementation in the VIIRS SDR operational processing in 2014. The presentation evaluates the changes in the VIIRS RSB coefficient updates and their potential impacts on application of the remote sensing measurements in the visible (Vis), near-infrared (NIR), and short-wave infrared (SWIR) bands throughout the two-year period of the Suomi NPP mission. Preliminary comparisons between the calibration coefficients generated by the RSBAutoCal and the current operational versions are also presented, as is the dependence of the radiometric calibration on processing coefficients such as attenuation screen transmittance and solar diffuser bidirectional reflectance.