Modeling of microwave scattering from ice crystal aggregates and melting aggregates: a new approach

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Description

Ice crystal aggregates and their melting process are modeled with a new approach for determining their microwave scattering characteristics and are compared with those obtained using effective dielectric constant representations. The aggregates are constructed from columnar crystals of random lengths (the width being a function of the length), which are composed of a string of touching ice spheres with diameters equal to the column’s width. The aggregates are melted using a model that incorporates the primary aspects of experimentally observed features of the melting process. The Generalized Multiparticle Mie (GMM) method is used for computing the scattering cross sections of the dry and melting aggregates. The T-matrix method is used for the calculations involving the effective dielectric constant models with oblate spheroidal shapes. The results obtained for 3 GHz and 35.6 GHz frequencies show significant differences in the backscattering cross sections. For sizes larger than 5 mm these differences range from several dB at 3 GHz to well over 10 dB at 35.6 GHz. Significant differences are also observed in the extinction cross sections during the melting process. It is concluded that the effective dielectric constant models of dry and melting ice crystal aggregates may not be representative of the interaction between the constituent crystals of the aggregates. Hence, bulk models must be used with caution depending on the electromagnetic wave frequency and the aggregate size range.