COMPARING GROUND-LEVEL SPECTRALLY RESOLVED SOLAR UV MEASUREMENTS USING VARIOUS INSTRUMENTS - A TECHNIQUE RESOLVING EFFECTS OF WAVELENGTH SHIFT AND SLIT WIDTH

Spectrally resolved UV measurements are important for the study of bio logically relevant UV in relation to changes in atmospheric parameters . The inter-comparison of spectral instruments is essential as measure ment techniques and calibrations are not standardized. The differences in slit functions cause large spectral variations when comparing the spectral readings directly. The method described, which compares spect ral readings using different instruments, corrects for differences of wavelength calibrations and slit functions, and does not require knowl edge of additional atmospheric parameters and UV-transfer model calcul ations. The wavelength alignment has an accuracy of 0.02 nm over the w avelength interval from 300-400 nm, and a reproducibility of 0.01 nm. The robustness of the methods and reproducibility of results are shown in the evaluation of a seven day intercomparison campaign with three different scanning spectroradiometers.