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Abstract

The study describes a new method to calculate electromagnetic scattering from small, arbitrary shaped particles. It is called the Green's dyadic technique for the transition operator (brie y the GDT-matrix). First, the method is introduced from the general theory of scattering (transition operator and Dyson equation) and then it is compared with existing electromagnetic scattering models. Second, the model is used to characterize small ice particles and to interpret single-particle scattering measurements made with the Small Ice Detector instrument (SID). In particular, the study is focused on small irregular particles with fractal shapes. We apply the Gaussian random sphere model in order to give an estimation of the particle roughness. The direct comparison of the forward scattered intensity as measured by SID and simulated by the GDT-matrix model leads to a retrieval of the size and shape of the scatterers. Third, the single particle results are statistically averaged to calculate many-particle optical properties in order to evaluate radiances through the radiative transfer Monte Carlo model McArtim. Further, the simulated radiances in near-infrared (NIR) are compared with measurements made during the NASA-ATTREX project on board the research unmanned aircraft Global Hawk. These comparisons lead to a remote retrieval of the thermodynamic phase of the constituent cloud particles and provide insights on the surface of the scatterers, i.e. rough or smooth.