| Raindrops became oblate spheroid in the falling process, so the scattering features of which must be considered when detecting precipitation areas with radar. This article is merely to give a short introduction to three very different types of methods for calculating non-spherical scattering properties:Gans theory, T matrix and DDA. Gans theory has accurate analytical solution for calculating the scattering properties of small ellipsoid and faster computation speed than T matrix and DDA. DDA is a powerful technique for calculating scattering and absorption by targets of arbitrary shapes and structures, but there is application restriction in the radar data processing quantitatively for time consuming and complicated codes. It’s studied that applicable range of Gans theory for calculating raindrop backscattering properties, establishment and usage of Quick Formulas sequential in this paper. The main conclusions are as follows:(1)The max applicable "size parameter" for computing backscattering cross section can be obtained when relative difference between both algorithms is more than10%for the first time by comparing Gans theory and T matrix at radar common wavelengths. Meanwhile, it is analyzed that the applicable ranges with the max size parameter effected by the different wavelengths. Theoretical calculation indicate that applicable size parameter x ranges from0.10to0.15at wave bands of S, X and C, which is larger than that under horizontal polarization, and which reaches0.38at wave band of Ka.(2)Quick Formulas based on DDA outputs is a set of partitioned polynomials aiming at easy-coding and time-saving during calculating extinction and backscattering properties for oblate spheroid raindrops. The Quick Formulas for the common radar wave bands of S, C, X, Ka and W have been obtained. It has been shown that the accuracy of Quick Formulas is more than95%, and the time consumed is negligible as compared with DDA computation, which has faster computation speed and more flexible portability.(3) Then the Quick Formulas at the wavelength of3.2cm are transplanted in the codes of radar data simulation to numerical calculate and analyze radar constant C as a function of rainfall intensity correlated with ellipticity, which is compared with the results of two other algorithms. For determining the inversion error of radar reflectivity factor caused by uncertain radar constant C, the study investigates that the effect on radar constant ratio γc brought when their shape factors and rain droplet size spectrum parameter is changing, which can be theoretical basis for the establishment of the polarization radar equations and redefinition of radar parameters such as Zhh,, Zvv and Zhv,... |
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