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                        Comparative Analysis of Raindrop Size Distribution Retrieval
                                  Techniques Based on Dual Polarization Radar


                                                          1, 2
                                           1, 2
                                 ZENG Jing , ZHANG Yang , SU Debin , DONG Yuanchang       4
                                                                      1, 3
                     (1. College of Electronic Engineering, Chengdu University of Information Technology, Chengdu  610225, Sichuan, China;
                           2. State Key Laboratory of Severe Weather Meteorological Science and Technology, Chinese Academy of M
                                              eteorological Sciences, Beijing  100081, China;
                      3. Key Laboratory for Atmospheric Sounding, China Meteorological Administration, Chengdu  610225, Sichuan, China;
                        4. Institute of Plateau Meteorology, China Meteorological Administration (CMA) / Heavy Rain and Drought-Flood
                            Disaster in Plateau and Basin Key Laboratory of Sichuan Province, Chengdu  610072, Sichuan, China)
             Abstract: Accurate retrieval of raindrop size distributions (DSDs) based on dual-polarization radar can provide
             substantial data for the study of precipitation microphysical properties on a large scale. In order to further im‐
             prove DSDs retrieval accuracy, this study proposes a new double-moment normalization method based on the
             sixth and seventh moments (M6M7 method), comparing it with the third and sixth moments method (M3M6
             method) and the constrained Gamma model DSD retrieval method (C-G method) from three perspectives: over‐
             all results, different rainfall intensities, and different rainfall particle sizes. Utilizing data from six rainfall events
             observed  by  dual-polarization  radar  and  surrounding  disdrometers  at  Heyuan  station  between  May  and  June
             2022,  the  retrieval  results  of  each  algorithm  were  analyzed. The  results  demonstrate  that  during  light  rain
                                 -1
             (0 mm·h <R≤5 mm·h ), the M6M7 method exhibits the smallest parameter biases among the three methods.
                      -1
             As rainfall intensity increases, biases for most parameters (except for the increase of liquid water content (LWC)
             and rainfall rate (R)) remain relatively stable, with M6M7 consistently showing the lowest biases across differ‐
             ent particle sizes and minimal fluctuation with the increase of particle size. Compared with M6M7 method, the
             M3M6 method incorporates specific differential phase shift on propagation (K ) for retrieval. Although K  is
                                                                                                           dp
                                                                                  dp
             noise-sensitive,  it  has  good  quality  in  heavy  rain (R>30  mm·h ),  resulting  in  smaller  estimation  biases  for
                                                                      -1
             intense rainfall events and a decreasing trend in bias with larger particle sizes (excluding LWC and R). For mod‐
                                           -1
                              -1
             erate rain (5 mm·h <R≤30 mm·h ), the C-G method shows small median deviations yet significant fluctuations
             in certain parameters. With the increase of rainfall intensity and particle size, its biases shows a trend of first
             decreasing  and  then  increase,  accompanied  by  pronounced  relative  bias  instability. Comprehensive  evaluation
             results  demonstrate  that  the  M6M7  method  consistently  maintains  median  deviations  approaching  0  across  all
             DSD  parameters,  while  exhibiting  significantly  tighter  error  fluctuation  ranges. In  marked  contrast,  both  the
             M3M6 method and C-G method display substantially wider bias variability, with their error distributions span‐
             ning  broader  numerical  ranges  and  demonstrating  less  stable  performance  characteristics. The  newly  proposed
             M6M7 method technique demonstrates advantages over traditional approaches, exhibiting enhanced comprehen‐
             sive retrieval capabilities with regard to both accuracy and stability, particularly excelling in light-to-moderate
             rainfall with consistent accuracy. The M3M6 method proves more effective for heavy rain and storms, while the
             C-G method demonstrates unstable retrieval characteristics. The final section demonstrates the retrieval perfor‐
             mance of the algorithm integrating both M6M7 and M3M6 methods, verifying its capability to further improve
             raindrop size distribution retrieval accuracy.
             Key words: raindrop size distribution; retrieval algorithm; dual-polarization radar
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