MICROWAVE ATTENUATION BY REALISTICALLY DISTORTED RAINDROPS .1. THEORY

By using a new raindrop model developed earlier and applying the first -order perturbation-expansion technique, the effects of realistic and nonaxisymmetric distortion of varying raindrop shapes on microwave att enuation are re-investigated in this paper, Under the assumption of no naxisymmetric raindrop scatterers, a system of general equations satis fied by the scattering and transmission coefficients of the electromag netic (EM) fields are derived under the zeroth-order and the first-ord er approximations, Both the horizontal and the vertical polarizations are discussed, The scattered and transmitted EM fields are obtained by means of expansion of spherical vector wave functions, Under the firs t-order perturbation approximation, the total cross section is calcula ted and discussed. Compared with the previous formulas presented for t he axisymmetric raindrop scattering, the new results of total cross se ction obtained here consist of two additional terms resulting from the nonaxisymmetric distortion, These additional terms due to the raindro p's nonaxisymmetry are represented analytically and discussed numerica lly. Part II of this paper will present an application of the analysis to the specific microwave attenuation due to rain in the moderate cli matic region and in Singapore's tropical region.