Calibration monitoring using laboratory and vicarious approaches on the DAIS 7915

Abstract

Laboratory and vicarious calibration is performed on a regular basis for the DAIS 7915 imaging spectrometer since 1995. The laboratory method includes spectrometric, geometric and radiometric calibration using the equipment of the Laboratory Calibration Facility at DLR. The imaging spectrometer, the laboratory equipment and the methodology have been improved over time to obtain data of increased quality and to enhance the calibration accuracy. The refinement of the calibration techniques revealed certain limits to absolute radiometric calibration. Issues such as the accuracy of calibration standards and the reliability of comparative measurements must be considered. The calibration processing has been reviewed and modified to ease in-flight calibration approaches through prior removel of Kennedy scanner artifacts. Vicarious calibration experiments are conducted in order to validate the laboratory calibration and, if appropriate, adapt it to in-flight conditions. A number of differernt calibration targets have been utilized. For all targets in-situ ground spectrometric measurements are available. The reflectance spectra have been modeled to at-sensor radiance using the MODTRAN radiative transfer code. Based on the comparison of modeled data with airborne imaging spectrometer measurements the laboratory calibration was validated or corrected. In 1997 the focus was laid on a campaign carried out in Israel. Despite the favorable conditions and the considerable effort spent on ground truth the accuracy obtained does not allow to bridge the gap between laboratory and vicarious calibration for the DAIS 7915. The remaining uncertainties conceal the true magnitude and the cause of the discrepancies.