Abstract
Archives of meteorological satellite imagery are recognized as valuable resources of the long-term Earth observations needed for characterization of the climate and detecting climate change. These applications require that the sensors on different satellites be calibrated to a consistent scale, and that the calibrations be maintained over the instruments' lifetimes. Because the visible-channel imagers on nearly all meteorological satellites have no on-board calibration capabilities, external calibration targets must be used for these wavelengths. The Moon appears regularly behind the Earth in the space-viewing margins of the field of regard of geostationary orbiting satellites, and lunar images are captured by chance with routine operational imaging schedules. In a study sponsored by the Climate Data Records Program (CDRP) at the NOAA National Climatic Data Center (NCDC), sensor response biases between visible channel imagers on geostationary satellites are being assessed using lunar images, processed and compared against the lunar radiometric reference provided by the USGS lunar calibration project (ROLO). The USGS system generates model predictions of the lunar spectral irradiance corresponding to the specific conditions of views of the Moon taken by instruments, for any time. These model results effectively normalize the varying brightness of the Moon, enabling cross-comparison of sensor calibration by reference against a common, stable source, and also revealing temporal response trends for each satellite. Results for GOES imagers and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on Meteosat-8 and 9 will be presented.
Cross-calibration of Geostationary Meteorological Satellite Visible Channel Imagers Using the Moon as a Common Reference
Archives of meteorological satellite imagery are recognized as valuable resources of the long-term Earth observations needed for characterization of the climate and detecting climate change. These applications require that the sensors on different satellites be calibrated to a consistent scale, and that the calibrations be maintained over the instruments' lifetimes. Because the visible-channel imagers on nearly all meteorological satellites have no on-board calibration capabilities, external calibration targets must be used for these wavelengths. The Moon appears regularly behind the Earth in the space-viewing margins of the field of regard of geostationary orbiting satellites, and lunar images are captured by chance with routine operational imaging schedules. In a study sponsored by the Climate Data Records Program (CDRP) at the NOAA National Climatic Data Center (NCDC), sensor response biases between visible channel imagers on geostationary satellites are being assessed using lunar images, processed and compared against the lunar radiometric reference provided by the USGS lunar calibration project (ROLO). The USGS system generates model predictions of the lunar spectral irradiance corresponding to the specific conditions of views of the Moon taken by instruments, for any time. These model results effectively normalize the varying brightness of the Moon, enabling cross-comparison of sensor calibration by reference against a common, stable source, and also revealing temporal response trends for each satellite. Results for GOES imagers and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on Meteosat-8 and 9 will be presented.