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Identification of Ground Clutter with C-band Doppler Weather Radar
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摘要: 地物回波对雷达数据应用会造成负面影响，是影响定量降水估测等产品精度的重要因素，识别并剔除地物回波是雷达基数据质量控制的一个重要内容。该文在现有S波段雷达地物识别方法的基础上，使用长治、哈尔滨两部CINRAD/CC雷达2011年观测数据，对C波段雷达地物回波特征进行分析，改进识别参量的隶属函数，建立适合C波段多普勒天气雷达的地物识别方法 (MCC方法)，并对该方法进行效果检验。结果表明：S波段及C波段雷达地物回波与回波强度有关的参量分布较为相近，与降水回波的参量分布有明显区别；S波段雷达地物识别方法中与回波强度有关的参量可用于C波段雷达地物的识别，与速度有关的参量中仅中值速度可用于C波段雷达。通过统计分析与个例分析，相对于现有S波段雷达识别方法，MCC方法可显著提高C波段雷达地物回波的识别正确率，并可减少层状云降水回波的误判。Abstract: The application of radar data is negatively affected by echoes caused by ground clutter, meanwhile these echoes from ground clutter have significant effect on rainfall estimation and radar data assimilation. As a result, it is important to identify and discriminate these echoes, which is an absolutely necessary part of radar data quality control. The ground clutter identifying algorithms in operation are mostly based on S-band Doppler weather radar, the resolution and velocity scanning mode of which are different from those of C-band radar. Few researches are carried out to discuss whether the method based on S-band is applicable to the C-band radar or not. Based on the current algorithm used for the SA radar, one method is developed for the CC radar using the data observed by radars of Changzhi and Harbin. The statistical characteristics of clutter are analyzed using data collected during 2011, and the membership functions are improved for C-band Doppler weather radar.Results show that, for S-band and C-band Doppler weather radar, parameters about reflectivity of ground clutter are similar, and there are notable differences between ground clutter and precipitation echoes. For C-band ground clutter echoes, the parameter TDBZ is greater than S-band. GDBZ value of both kinds of radar is alike, mostly below 0. SPIN value of ground clutter echoes is remarkably greater than that of precipitation echoes for both C-band and S-band radar. It shows that three parameters about reflectivity including TDBZ, GDBZ and SPIN, can be used to identify and discriminate C-band radar ground clutter echoes.For C-band radar ground clutter and precipitation echoes, only MDVE, associated with velocity, could be used to distinguish these two kinds of echoes. For MDSW and SDVE, there is no notable difference between ground clutter and precipitation. In contrast, two parameters of ground clutter are different from that of precipitation echoes for S-band radar. For S-band radar, MDSW and SDVE are both very small, mostly below 1. There are considerable numbers of values above 1 for two parameters of C-band radar. The spatial resolutions of two kinds of radars are different, which may result in the fact that MDSW and SDVE could not be used to distinguish ground clutter echoes from precipitation echoes. Besides, the velocity scan mode, the dual pulse repetition frequency may cause the phenomenon to some extent. It can also be caused by the different precisions of two kinds of radars. The velocity precision of S-band radar is 0.5 m·s-1, while the velocity of C-band radar is 0.1 m·s-1. For S-band radar, the velocity changes more smoothly than that of C-band radar. Compared with the method based on S-band radar, the identification accuracy of ground clutter is improved notably and the false detection of stratiform cloud echoes is also reduced obviously.
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Key words:
- ground clutter;
- fuzzy logical;
- quality control
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图 1 2011年7月2日07:00长治雷达观测数据 (距离圈间隔50 km)
(a)0.5°仰角反射率因子, (b)0.5°仰角径向速度, (c) 0.5°仰角回波分类
(AP为地物，CA为晴空回波，SC为层状云，CC为对流云)Fig. 1 PPI of Changzhi radar at 0700 BT 2 Jul 2011 (range rings at 50 km intervals)
(a) reflectivity at 0.5° elevation, (b) radial velocity at 0.5° elevation, (c) echo classify at 0.5° elevation
(AP shows ground clutter, CA shows clear air echoes, SC shows stratiform cloud, CC shows convective cloud)
图 2 各参量的概率分布
(AP为地物，CC为对流云，SC为层状云)
Fig. 2 Probability distribution of characteristic parameters
(AP shows ground clutter, CC shows convective cloud, SC shows stratiform cloud)
图 3 VD的概率分布 (a) 及其小于某值的样本比例 (b)
Fig. 3 Distribution of VD (a) and percentage of VD below some value (b)
图 5 2011年07月25日07:01哈尔滨雷达识别效果 (距离圈间隔50 km)
(a)0.5°仰角反射率因子, (b)0.5°仰角径向速度, (c)1.5°仰角反射率因子，(d)1.5°仰角径向速度, (e) MSA方法识别后0.5°仰角反射率因子, (f) MCC方法识别后0.5°仰角反射率因子
Fig. 5 PPI of Harbin radar at 0701 BT 25 Jul 2011(range rings at 50 km intervals)
(a) reflectivity at 0.5° elevation, (b) radial velocity at 0.5° elevation, (c) reflectivity at 1.5° elevation, (d) radial velocity at 1.5° elevation, (e) reflectivity at 0.5° elevation after echo identification with MSA, (f) reflectivity at 0.5° elevation after echo identification with MCC
图 6 2011年7月2日07:05长治雷达识别效果
(a)0.5°仰角反射率因子, (b)0.5°仰角径向速度, (c)1.5°仰角反射率因子，(d)1.5°仰角径向速度, (e) MSA方法识别后0.5°仰角反射率因子, (f) MCC方法识别后0.5°仰角反射率因子
Fig. 6 PPI of Changzhi radar at 0705 BT 2 Jul 2011(range rings at 50 km intervals)
(a) reflectivity at 0.5° elevation, (b) radial velocity at 0.5° elevation, (c) reflectivity at 1.5° elevation, (d) radial velocity at 1.5° elevation, (e) reflectivity at 0.5° elevation after echo identification with MSA, (f) reflectivity at 0.5° elevation after echo identification with MCC
图 7 2011年6月3日11:05哈尔滨雷达识别效果 (距离圈间隔50 km)
(a)0.5°仰角反射率因子, (b)0.5°仰角径向速度, (c)1.5°仰角反射率因子，(d)1.5°仰角径向速度, (e) MSA方法识别后0.5°仰角反射率因子, (f) MCC方法识别后0.5°仰角反射率因子
Fig. 7 PPI of Harbin radar at 1105 BT 3 Jun 2011(range rings at 50 km intervals)
(a) reflectivity at 0.5° elevation, (b) radial velocity at 0.5° elevation, (c) reflectivity at 1.5° elevation, (d) radial velocity at 1.5° elevation, (e) reflectivity at 0.5° elevation after echo identification with MSA, (f) reflectivity at 0.5° elevation after echo identification with MCC
表 1 各参量识别正确率 (单位:%)
Table 1 Identifiable accuracy of each characteristic parameter (unit:%)
参量 总样本正确率 地物识别正确率 对流云误判率 层状云误判率 TDBZ 98.4 97.0 1.84 0.12 GDBZ 91.7 82.7 2.1 5.5 SPIN 97.4 96.1 3.0 1.0 MDVE 92.8 89.1 4.7 5.9 
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表 2 整体识别正确率 (单位:%)
Table 2 Identifiable accuracy for ground clutter echoes and false detection of precipitation echoes (unit:%)
识别方法 总样本正确率 地物识别正确率 对流云误判率 层状云误判率 MCC 99.2 97.8 0.31 0.03 MSA 87.4 62.3 0.03 0.18 MSC 98.5 97.9 1.64 0.69
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