Integral equation approximation to microwave specific attenuation by distorted raindrops: the Pruppacher-and-Pitter model

An integral equation approximation that combines the scattering-radiation conversion, the small perturbation technique and the spherical vector eigenfunction expansion method is employed in this paper to investigate the radio wave attenuation by a realistically distorted scatterer, i.e. the Pruppacher-and-Pitter (P-P) model raindrop. A simple and modified non-symmetric model that fits the Pruppacher-and-Pitter distorted rain-drop shapes by means of least squares is used in the calculation. The scattered electromagnetic fields are integrated from the scattering dyadic Green's function and the volumetric current distribution of an assumed point source that generates the plane waves. Moreover, the scattering coefficients are derived. Total (extinction) cross sections (TCSs) of the realistic P-P model raindrops at the frequencies of 15, 21.225 and 38 GHz are computed and compared with those of spheroidal raindrops. The specific microwave attenuation of a plane wave due to the P-P model raindrops are calculated numerically and compared with both measured data and the computed attenuation due to spheroids. Comparison shows a slight difference between the computed results obtained using spheroidal raindrops and the P-P model raindrops; and close agreement between the computed results and the experimental data.