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