Measurements of both UV B (280 – 315 nm) and UV AB (280 – 400 nm) irradiances taken during about seven years are presented and analyzed here. The UV irradiance data were measured with MACAM radiometers, which are installed in the Atmospheric Physics Observatory of the University of Èvora Geophysics Center - CGE (38°34’N, 7°54’W, 300 m above mean sea level) since 2004. Special attention is devoted to calibration issues, since the radiometers were calibrated in Spain, at “El Arenosillo” ESAt/INTA laboratory in 2009 and a methodology based on radiative transfer calculations combined with observations from atmospheric quantities, was developed and applied to retrocalibrate the data from 2009 to 2004. The comparison between the radiative transfer based and the laboratory calibration methodologies yielded a quite promising outcome, with normalized root mean square errors lower than 3% and mean absolute percentage errors lower than 2%. Cloud optical thickness values derived from ground-based spectral irradiance measurements taken at the CGE observatory, are also used in order to investigate the influence of this cloud quantity on UV irradiances.

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