Hydrometeor Phase Identification Method (HC) Analysis And Parameter Improvement

This article was completed under the support of the National Key Research and Development Program.Through these polarization parameters,more information can be obtained about the size,phase state,and shape of the hydrogel particles information.In addition,the radar observation data has a high spatial and temporal resolution,which is beneficial to observe the changes of cloud internal structure and the generation and dissipation of water condensate.Therefore,dual-polarization radar has become an important tool to improve the level of phase recognition and precipitation estimation.Most of the recent hydrometeor classification schemes are based on fuzzy logic.Due to the lack of true value of hydrometeors,it is difficult to verify whether classifications are right or not.Therefore,three methods are proposed,cumulative value test,algorithm sensitivity test and hydrometeors' distribution test.(1)Cumulative value test is used to inspect the ability of classifying and distinguishing.When input data contains system deviation and noise,the output classification would also contain system deviation and noise.Thence,a method is proposed to test the sensitivity of system deviation and noise.(2)Hydrometeors distribution test is to analyze whether the hydrometeor distribution is temporal and spatial continuous.Through these tests the reliability and stability of the algorithm are analyzed,and key factors which affect the classification can be found out.(3)Compared with conventional Doppler radar,dual-polarization radar uses its own characteristics to extract polarization parameters that reflect the difference between the signals of the two channels.The main research object of precipitation particle phase state recognition is the water condensate in the cloud(rain,snow,hail,etc.).The accurate data on the distribution of water condensate can help to study the physical process,microphysical process and moisture of the cloud at the macro and micro levels Transformation of phase.Among the phase recognition methods based on dual polarization radar,fuzzy logic precipitation particle phase recognition method is the most widely used.Although the research and application of this method have achieved good results,there are still problems and limitations.Regarding the stability of the method,how to determine the effect of the observation error on the recognition effect,how to determine the accuracy of the method,how to determine the optimal fuzzy logic rules,and how to determine the reliability of the method,how to determine whether the recognition results conform to the physical laws.(1)Using cumulative value test,some hydrometeors are found out with inappropriate membership function.These membership functions are not consistent with the real characteristics of hydrometeors,which are ground clutter(including that due to anomalous propagation),biological scatters,dry aggregated snow,crystals of carious orientations,light and moderate rain,and a mixture of rain and hail.The way to modify these membership functions is based on hydrometeor statistic characteristics.(2)Another insufficiency of membership function is to distinguish similar hydrometeors,such as crystals of various orientations with dry aggregated snow and heavy rain with mixture of rain and hail.The method to modify membership function's distinguishing ability is increasing the parametric weights which has stronger discriminating ability.(3)To ensure every hydrometeor has more than 90% stable results,the data error of Zh is-0.5d B-+ 0.5 d B,that of ZDR is-0.1d B-+0.1 d B,that of ?hv is less than 0.02,and that of KDP is between-0.3 d B and +0.9 d B.Moreover,data quality of Zh and ZDR is more important than other parameters,system deviation is more influencing than noise.After hydrometeors' distribution test,it is found that heavy rain may be misclassified as mixture of rain and hail.The spatial consistency correction method is to check whether the distribution of mixture of rain and hail in a certain space is continuous.Using observations of precipitation processes in Guangzhou in spring and summer from 2016 to 2017,the efficiency of S-band dual-polarization doppler radar is examined.Main results show that the classifying hydrometeor relies on the membership function.The method can better identify the phase state of the precipitated particles,especially the phase state identification in the process of strong convection,which has very important significance for predictive physics research and prediction.