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Intercomparison of ultraviolet spectroradiometers

The main objective of the project was to achieve and maintain high quality standards in spectral UV measurements performed in Europe, which would significantly contribute in the establishment of a European monitoring network. This objective was met through the organization of an international intercomparison campaign of ultraviolet spectroradiometers. During the campaign different types of instruments operating regularly at different locations, were brought together and operated independently side by side to investigate the degree of their agreement and asses the causes of possible deviations. Nineteen spectroradiometers from 12 European and three overseas countries ensured the widest possible geographical coverage and the largest available diversity of instrument types. From the analysis of the results valuable information were gathered, regarding the technical behaviour of each instrument and the operational procedures followed by their operators. In summary, the results obtained during the two days of blind intercomparison demonstrated a marked improvement on those of previous campaigns, with more instruments achieving stable and repeatable measurements. All 19 instruments produced a full set of spectral data, and there were no large unexplained diurnal or spectral anomalies. The remaining discrepancies between the instruments were mostly due to the absolute spectral irradiance calibration, which still seems to defeat some operators, especially at the shortest wavelengths. Fifteen of the instruments agreed to within 13% relative to a comparison reference. All but four of these fell within 7% of the reference at wavelengths greater than 305 nm and at noontime, 11 instruments were within 5%. Of these 11 instruments, seven came within 3% of the norm, and three instruments were within 1% or 2%, which is comparable with the current resolution of the intercomparison technique. The diurnal variations of most of the instruments did not exceed 5%, relative to the reference spectra, and the same was true of their spectral variations.

Reported by

Aristotle University of Thessaloniki
54006 Thessaloniki
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