This work is focused on electromagnetic scattering models by irregular ice hydrometeors, particularly pristine ice crystals and their aggregates. Studies are available in literature with focus on electromagnetic techniques such as FDTD, DDA, CDA, T-Matrix, Mie, GMM, for both pristine ice crystals and aggregates (Aydin, 1999; Liu, 2008; Petty and Huang, 2010). A summary of these models and comparisons of the results are given in this work. One of the results of this work relates to the effect of a soft sphere approximation on the scattering properties of a target, in particular ice aggregates. The soft sphere approximation consists of modeling a given target with a sphere or a spheroid with an appropriate effective dielectric constant. Several results show that this approximation fails to correctly model ice aggregates when the size of the sphere or spheroid along the propagation direction is roughly half the wavelength and larger. In fact, the assumption of a solid shape instead of a more complex one leads to characteristic interference effects in the scattered field, showing a typical resonating behavior leading to an underestimation of the back-scattering cross section. It has been shown that the use of other methods leads to large differences for aggregates (Botta et al., 2010; 2011). For example, considering a low density ice aggregate with a maximum dimension of 2 mm and a wavelength of 3.19 mm (W band), using the soft sphere approximation leads to an underestimation of the back-scattering cross-section between 5 and 15 dB, depending on the parameters of the soft sphere, if compared to the methodology developed by Botta et al. (2010; 2011). The scattering behavior of a soft spheroid approximation also depends on the choice of the aspect ratio and on the radiation incidence angle. A commonly used aspect ratio of 0.6 leads to an underestimation close to 5 dB at vertical incidence, and reaches 15 dB at side incidence. This work further analyzes the issue and compares several different electromagnetic models.

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