Retrieval of aerosol optical properties and estimation of aerosol forcing based on multi-spectral sun photometer observations.

We discuss an inversion method to retrieve aerosol optical properties based on direct and diffuse multi-spectral observations of solar radiation at the Earth's surface. These radiation quantities are measurement by a sun spectrometer with CCD spectrometer. The spectral range of the instrument detector is between 350 and 1100 nm and includes 255 channels. This instrument is operated with two modes; one with active solar tracking which allows measure direct solar radiation and second with almucantar or principle plane scans which are used to measure spectral sky radiance. Based on this we retrieve spectral aerosol optical thickness, columnar single scattering albedo and asymmetry parameter but also the total water vapor. Finally based on retrieved parameters and calculations of radiation fluxes for atmosphere without aerosol the aerosol forcing at the surface is estimated.