Modeling of backscattering by non-spherical ice particles for the interpretation of cloud radar signals at 94 GHz. An error analysis

Backsacttering by non-spherical ice particles at 94 GHz (3.2 mm wavelength) has been examined for hexagonal cylinders with aspect ratios ranging from 0.2 to 10, ie from plate-like to needle-like particles, as well as for combinations of hexagonal columns. Calculations have been performed using the Discrete Dipole Approximation (DDA). The results are of particular interest for the recently available 94 GHz cloud radar systems. In order to estimate the required number of dipoles to model a given particle, two empirical criteria have been formulated, which take into account the size and the non-sphericity of the particle. The origins of errors in the DDA method have been investigated. The effects of neglecting higher orders of multipole terms are much smaller than the errors due to the approximation of the particle shaping by arranging dipoles on a cubic array. The backscattering properties of horizontally oriented ice particles have been calculated. Both the backscattered radiance and the depolarization ratio strongly depend on the particle size and aspect ratio. -Authors