Non-spherical Particle’s Scattering Properties And The Applications In Radar Bright Band Study

The physical properties of hydrometeor, i.e. the phasestate, size, morphology, are related to its scattering features. The influence of morphology on scattering features is one of the hot and difficult problems of scattered research. Because the calculation of the multiphase non-spherical particle’s scattering characteristics has been too complicated and time-consuming, the quantitative research on multiphase non-spherical particle’s scattering properties and its applications on radar detection have long been obstructed.Based on the Gans theory, the scattering features of an individual small oblate raindrop has been discussed. The relationship between the orientation of scattering maximum and its axis ratio for different polarized incident waves has been derived and the effect of the axis ratio on the elevation of the scattering maximum has been calculated. The results are used in the analysis on the detecting ability of bistatic dual-polarization radar system, and provide a theoretical base for improving the detecting accuracy of bistatic polarization radar. In addition, in order to deeply study the mixed phase non-spherical particle’s scattering characteristics, the standardized backscattering cross section for oblate ice particle enclosed with liquid water has been calculated with DDA. After adding the cauculated results into the SimRAD (Simulating Radar detection and Data processing) software, the vertical radar reflectivity factor profile with consideration of the melting layer has been simulated. Comparing the simulation results with practical radar observation data, the effects of non-spherical particle on radar bright band are analyzed. The purposes of this research are enriching the cloud and precipitation physics and detection theory, and providing a reference for further reserch on microphysical process of radar bright band. Main concusions as follows:(1) Assuming that the rotary axis of the raindrop is upward, the orientation of scattering maximum is different from incident direction under vertical polarization incident and scattered waves, the scattering characteristic is closely related to incident elevation. The elevation of scattering maximum is increasing with the axis ratio.(2) The detection capability of bistatic polarization radar may affected by the elevation of the radar antenna, the position of target droplets and the scatted ability of raindrops, when radar detect oblate raindrops. The area of low echo near active radar and high echo near passive radar are all reduced as the elevation lifted.(3) Sphere ice particles which stay above bright band will transform into oblate ice particles enclosed with liquid water during the falling and melting process. This paper bulit a quick formula which can calculate standardized backscattering cross section for oblate ice particles enclosed with liquid water, and put this quick formula into SimRAD for simulating the vertical radar reflectivity factor profile with consideration of the melting layer. The results show that the simulation results fits the echo of the practical radar observation data better when we consider that the ice particles enclosed with liquid water are oblate.