Abstract: The need is identified for a unified approach to thepreflight and in-flight absolute radiometriccalibration of satellite sensors, which does not dependon the accurate transfer of lamp and detectorcalibrations from the laboratory to orbit. Such anapproach is described that uses the sun to provide thelink between preflight solar-radiation-basedcalibration, in-flight solar- diffuser-basedcalibration, and vicarious calibration. An example isgiven of each of these methods and uncertainty budgetsare provided. It is shown that an uncertainty, withrespect to solar exo-atmospheric irradiance, of lessthan 3%, one sigma, can be attained for each method andthat each can, if needed, be related to nationallaboratory standards. In addition to providing the linkbetween preflight and in-flight on-board calibrations,this unified approach also fills the critical need torelate these calibrations to those of the radiometersused for vicarious calibration and data-product,field-validation measurements, by also referencing themto the same solar-irradiance scale. !15
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