Experimental errors in sun-sky radiometer measurements

Sequential measurements of direct and diffuse solar radiation for each scattering angle in the visible and near infrared region, were carried out with the ground based sun-sky radiometer Prede, in order to determine directly in situ the instrumental errors. The sensitivity of the code Skyrad 3, produced by T. Nakajima, to the experimental errors has been studied in this work. The uncertainty on the retrieved columnar aerosol volume distribution, aerosol optical thickness, single scattering albedo, and phase function, was obtained for each wavelength. Measurements were taken in two locations with very different atmospheric characteristics: Antarctica and Rome, Italy. The method used for the determination of experimental error showed to give good results, independently of the location. The uncertainties obtained for the quantities retrieved by Skyrad 3, are independent of the atmospheric turbidity and, possibly, they can be assumed as general accuracy levels.