An efficient calculational approach to evaluation of microwave specific attenuation

An efficient calculational approach using the scattering-radiation conversion is developed in this paper to evaluate the microwave attenuation by arbitrarily distorted raindrops. For this modified first-order approach, the perturbation technique and the spherical vector eigenfunction expansion method are employed. A method of obtaining the volumetric current distribution of the assumed source that generates the plane waves is developed in the paper and the current distribution of such a source is derived. The electromagnetic fields outside the distorted raindrop scatterers are formulated in terms of integrals consisting of a volumetric current distribution located at infinity and the dyadic Green´s functions. To illustrate the validity of this approach, the spheroidal raindrop and the Pruppacher and Pitter (1971) raindrop model of varying shapes are specifically investigated. Numerical results of the extinction cross sections and the specific attenuation due to the two models are obtained. While the former agrees well with the published results, the latter is in good agreement with the experimental specific attenuation data collected at 21.225 GHz in Singapore.