An aureole-corrected Langley-plot method developed for the calibration of HiRES grating spectrometers

Ground-based sensors for the vicarious calibration of spaceborne Earth remote-sensing spectrometers must be Sun-calibrated for measurements of direct solar irradiance spectra. The best results for Sun calibration control gives the classical refined Langley-plot analysis at high altitude clean air sites. This analysis fails in general for near sea-level measurements due to unstable atmosphere and inhomogeneous layers during a calibration phase. Adding solar aureole measurements to the Langley analysis, the Sun calibration can be realized even at near sea-level locations and during ground-truth campaigns. The first measurements for such an aureole-corrected Langley-plot analysis have been realised with the HiRES ( Hi gh R esolution E nvironment S pectrometer) grating spectrometers. Results of aureole-corrected Langley-plot measurements carried out in Berlin (60 m above sea level, a.s.l.), Germany, are compared with a reference classical Langley calibration using data measured at the Jungfraujoch observatory (3580 m a.s.l.) in the Swiss Alps.