Aerosol optical properties retrieved from solar aureole measurements over southern Sardinia

Combined experiments on the aerosol properties were carried out with a solar aureolemeter, a Sun photometer, three aeresol cascade impactors, and the satellite advanced very high resolution radiometer data, in Cagliari and Carloforte, southern Sardinia, in May and June 1994. The experimental data of the aureolemeter, which operates in the wavelength range from the UV to the near-IR, are analyzed in this paper. The equivalent refractive index of the aerosol particles and the equivalent ground albedo are derived with the inversion library method. With the equivalent refractive index and the equivalent ground albedo, the optical properties of the aerosols, such as the size distribution, the optical thickness, and the single-scattering phase function are retrieved by an updated code, which employs a radiative intensity transfer algorithm and a nonlinear iterative inversion procedure. The columnar aerosols detected in this region have a trimodal size distribution with the volume mode radii located at about 0.15, 0.5; and 2.0 mu m; they present the typical maritime aerosol characteristics. The behavior of the aerosol optical thickness is described through its variations in 2 entire days. From this experiment we found that for the measurement of the diffuse solar radiation, three operational wavelengths in the UV, the visible, and the near-IR are sufficient to obtain satisfactory information on the aerosol optical properties in the spectral range covered by these wavelengths.