Traceable radiance source for spectroradiometer calibration

SI traceable calibration of satellite instruments like spectroradiometers get increasingly important in space-based observation for various reasons. First, requirements on measurements in terms of accuracy, dynamic range and wavelength range get increasingly demanding. Second, long term observations require SI traceability for comparability of data records that have been acquired over a long time interval (decades) and with different instruments. In this contribution we outline an approach for radiance calibration of spectroradiometers with a wavelength-tunable radiance source. The radiance source is based on an integrating sphere and a widely tunable laser (UVN-SWIR) and will be calibrated against a set of reference detector standards. By offering the radiance source as a stimulus to the spectroradiometer under test, the instrument can be calibrated for spectral radiance response. Potentially this traceability route could lead to a reduced measurement uncertainty compared to the traditional FEL-lamp based method. Furthermore, other instrument characteristics can also be derived from the same set of measurements, like stray-light effects and the instrument response function.