A quantitative comparison of α-Å turbidity parameter retrieved in different spectral ranges based on spectroradiometer solar radiation measurements

Spectroradiometric direct irradiance measurements in the 300-1100 nm wavelength range with a spectral resolution of 6.2 nm have been used in a study of the variation in the Angstrom turbidity parameter alpha and its dependence on the spectral range used in its determination. The measurements have been carried out under clear sky conditions at two different climate stations in Spain. Least-square fits of the experimental spectral aerosol optical depth (AOD) to the Angstrom formula in different spectral ranges, selected for convenience depending on the objective or application (e.g., UV-VIS (350-400 nm), VIS (400-670 nm), VIS-NIR (370-870 nm), etc.), result in different sets for the alpha parameter. Due to this dependence on the spectral range, where the alpha -values are determined, a quantitative comparative analysis is carried out in order to assess the differences for a given data-base covering very different atmospheric conditions. The study reveals the necessity of a 'standard spectral range' to achieve confident data comparisons. We show some applications that are relevant for aerosol studies, from UV absorption by aerosols to satellite remote sensing. (C) 2001 Elsevier Science Ltd. All rights reserved.