Identification and Removal of Non-meteorological Echoes in Dual-polarization Radar Data Based on a Fuzzy Logic Algorithm

A major issue in radar quantitative precipitation estimation is the contamination of radar echoes by non-meteorological targets such as ground clutter,chaff,clear air echoes etc.In this study,a fuzzy logic algorithm for the identification of non-meteorological echoes is developed using optimized membership functions and weights for the dual-polarization radar located at Mount Sobaek.For selected precipitation and non-meteorological events,the characteristics of the precipitation and non-meteorological echo are derived by the probability density functions of five fuzzy parameters as functions of reflectivity values.The membership functions and weights are then determined by these density functions.Finally,the nonmeteorological echoes are identified by combining the membership functions and weights.The performance is qualitatively evaluated by long-term rain accumulation.The detection accuracy of the fuzzy logic algorithm is calculated using the probability of detection（POD）,false alarm rate（FAR）,and clutter–signal ratio（CSR）.In addition,the issues in using filtered dual-polarization data are alleviated.

Improved Algorithms for Removing Isolated Non-Meteorological Echoes and Ground Clutters in CINRAD

Using China New Generation Weather Radar （CINRAD） level-Ⅱ data, the original algorithms for removing isol-ated non-meteorological echoes and ground clutters in radar data, which have been applied to Weather Surveillance Radar-1988 Doppler （WSR-88D） in the USA and Severe Weather Automatic Nowcast （SWAN） system in China, are modified and improved. To remove isolated non-meteorological echoes, the new algorithm introduces a constraint parameter （Po） to distinguish whether a window of 5 x 5 points is isolated as external echoes. A statistical analysis of 150 radar scans （5 cases, with each case comprising 30 scans） under three different echo types （small-scale convec-tion, typhoon, and large-scale synoptic system） shows that the constraint parameter Po ≤ 0.167 is suitable for remov- ing isolated non-meteorological echoes while preserving the edge of meteorological echoes. A new parameter, NDZ, which promotes the ability of the algorithm to identify the ground clutters appearing at two adjacent elevation angles, is constructed based on the vertical continuity of reflectivity. These improved algorithms are tested for four cases （three cases of isolated non-meteorological echoes and one case of ground clutters）. Based on the statistics of 232 volume scans of radar data （on a temporal resolution of 1 h） measured at Nanchang station from 0000 UTC 5 to 1600 UTC 14 March 2015, it is found that the improved algorithms not only eliminate most （over 95% under clear-sky conditions） of the isolated non-meteorological echoes and ground clutters （including those appearing at two adjacent elevation angles）, but also well preserve the structure of meteorological echoes （storms）.