Exploitation of spectral direct UV irradiance measurements

Because of both scattering and absorption, ozone and aerosols lead to an attenuation in the surface UV irradiance. These factors can be efficiently retrieved from ground-based measurements of the spectral direct UV irradiance performed by using spectroradiometer systems. In this paper, we applied a Monte Carlo based exploitation technique of spectral direct UV irradiance measurements, which allowed us to obtain a bound within which the retrieved parameter (either the ozone column or an aerosol property) is expected to lie with a relatively high probability. The applied exploitation technique required sequentially comparing the ground-based measurements with a large number of spectra, each of them calculated by a radiative transfer model with randomly generated values of input parameters (i.e. the ozone column and aerosol properties). The dispersion of the generated values that led to acceptable matches between the measured and calculated spectra allowed us to compute both the estimates and the uncertainties of the retrieved parameters. The applied exploitation technique enabled us to describe the uncertainty propagation through the retrieval process and to assess the influence of the involved uncertainty sources. Methodological details are provided.