Comparison of the Ångström parameters retrieval in different spectral ranges with the use of different techniques

Abstract

Ground-based spectroradiometric measurements obtained in Athens have been used in order to derive the aerosol optical depth and the Angstrom parameters. Their derivation is achieved using three well-established and widely used techniques; the Volz method, the direct method and the least-squares fit to the experimental aerosol optical depth values. This study aims at investigating the ability of the different methods to derive similar Angstrom turbidity coefficients and their dependence on the spectral range used for their determination. In addition, the uncertainties revealed especially in the UV spectral band are highlighted. The various techniques lead to different Angstrom turbidity coefficients especially if narrow spectral bands at the shorter wavelengths are used. It is also established that the Angstrom turbidity coefficients derived by any of the three methods at short wavelengths are not representative of the whole spectrum, while their derivation exhibits large uncertainties especially under low turbidity conditions. Therefore, the comparison of α and β values obtained using the three above-mentioned techniques in several spectral bands is not an easy task, since these values differ significantly. From the whole analysis it is established that the least-squares method is the least imprecise, also exhibiting the least wavelength dependence.