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Comparisons of Doppler Spectral Density Data by Different Bands Pointing Vertically Radars
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摘要: 衰减对回波的影响是雷达探测中的一项重要课题，常用订正方法还有很大提升空间。由于垂直指向雷达观测的功率谱数据包含了非常丰富的微物理及动力信息，该文尝试在功率谱层面对衰减影响机理进行深入讨论，以期改进衰减订正方法。对2014—2016年广东阳江和广东龙门获取的Ka波段毫米波雷达、C波段调频连续波雷达、Ku波段微雨雷达功率谱数据进行对比表明：3部雷达功率谱谱型基本一致，具有一定可靠性。米散射效应反映在功率谱上即经过某一速度后回波强度谱密度的陡降，当降水下落末速度达临界速度时，会对衰减量的计算造成影响。雷达波长越短，受衰减影响越大，衰减对功率谱的影响表现为谱的整体下移，最终导致回波强度小于真值。对于对流云降水，单纯使用经验订正公式获得的结果可能与真实值相差很大，此时需要考虑降水粒子谱分布，在功率谱层面上对订正进一步改善。
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关键词:
- Ka波段毫米波雷达;
- C波段调频连续波雷达;
- Ku波段微雨雷达;
- 功率谱密度;
- 衰减影响
Abstract: The attenuation of the radar echo has always been a difficult problem in radar detections. Results corrected by the common methods have some differences with the real detecting value. Due to the richness of the micro physical and dynamic information by the power spectrum data of vertical detecting radars, the mechanism of attenuation could be investigated in the power spectrum layer. And then, a direction of the improvement of attenuation correction could be found by power spectrum data.Comparative research is carried out using the power spectrum data by Ka-band millimeter-wave radar, C-band frequency-modulated continuous-wave radar and Ku-band micro rain radar at Yangjiang of Guangdong during May-June in 2014 and Longmen of Guangdong during April-May in 2016. The power spectrum shapes by three radars are almost consistent, especially for the peak velocity and the first atmospheric signal, indicating data of three radars are reliable. In the detection of big particle size precipitation, the radar echo is affected by Mie scattering effects, especially shorter wavelength echoes. The reflect of Mie scattering effects on the power spectrum is a rapid decline of echo intensity during a speed point, which shrink the tail end of the spectrum, reduce signal spectrum width and affect the intensity value. The performance of power spectrum is the overall down of spectrum, and it leads to underestimation. In convective cloud precipitation detections, results calculated by the normal empirical formula may have difference with real value. Spectrum distribution could be taken into account in such condition, and the correction methods should be improved by the power spectrum density layer.Finally, the study of the attenuation correction, especially the study in the strong precipitation process, the power spectrum data could be used. But the question how the attenuation effect the power spectrum, the study just offers a direction. It still needs to explore in the quantitative research. -
图 1 广东阳江气象观测场和广东惠州龙门气象观测场位置
Fig. 1 The location of Yangjiang and Longmen detection fields in Guangdong
图 2 3部雷达在2.0 km高度处进行3 min时间平均且订正后的静止大气下回波强度谱密度对比
Fig. 2 Comparisons of 3 min averaged and corrected echo intensity spectrum data of three radars in static atmosphere at 2.0 km height
图 3 Ka波段(a)、Ku波段(b)、C波段(c)雷达回波分别通过瑞利散射和米散射计算的后向散射截面随粒子半径变化对比
Fig. 3 Comparsions of back scattering cross section calculated by Rayleigh scattering and Mie scattering in a increasing radius among echoes of Ka-band(a), Ku-band(b) and C-band(c) radars
图 4 3部雷达不同降水过程中3 min平均且订正后回波强度谱密度随高度变化
Fig. 4 Comparisons of 3 min averaged and corrected echo intensity spectrum density of three radars in different precipitation processes
图 5 2016年5月15日对流云降水过程中2.0 km(a)、2.5 km(b)、3.0 km(c)、3.5 km(d)、4.0 km(e)高度处CR与CWR回波强度谱密度对比
Fig. 5 Comparisons of the echo intensity spectrum of CR and CWR at the height of 2.0 km(a), 2.5 km(b), 3.0 km(c), 3.5 km(d) and 4.0 km(e) in the convective cloud precipitation process on 15 May 2016
表 1 Ka波段毫米波雷达、C波段调频连续波雷达、Ku波段微雨雷达技术指标
Table 1 Specifications of Ka-band millimeter-wave radar, C-band frequency-modulated continuous-wave radar and Ku-band micro rain radar
指标 Ka波段毫米波雷达 C波段连续波雷达 Ku波段微雨雷达 雷达体制 脉冲多普勒、单发双收、线性极化、全固态 连续波体制 脉冲多普勒、固态发射机体制 工作频率 33.44 GHz±10 MHz 5530±3 MHz 24.23 GHz 探测方式 垂直探测 垂直探测 垂直探测 探测要素 功率谱密度、回波强度、径向速度、
速度谱宽、退偏振比功率谱密度、回波强度、
径向速度、速度谱宽、回波功率功率谱密度、回波强度、
雨强、液态含水量、雨滴谱探测范围/km 0.03~15.3 0.03~15 0.1~3.1 FFT谱点数 256 512 64 时间分辨率 8.8~8.9 s完成3个模式扫描，每个模式约3 s 3 s，6 s 60 s 高度分辨率/m 30 30 100 波束宽度/(°) 0.3 2.6 2.0 
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表 2 2.0 km高度处3部雷达谱参数对比
Table 2 Power spectrum parameters of three radars at 2.0 km height
个例 过程类型 设备 回波强度/
dBZ功率谱峰值
速度/(m·s-1)信号谱宽度/
(m·s-1)米散射临界
速度/(m·s-1)临界半径/mm 2016-05-16
龙门低层积云 CR -14.7 0.6 1.2 CWR -15.2 0.6 1.3 2014-06-09
阳江层状云降水 CR 18.7 6.0 4.7 7.0 1.13 MRR 19.0 6.1 5.1 CWR 19.0 6.0 4.9 2014-06-09
阳江对流云降水 CR 24.5 7.0 5.9 7.1 1.16 MRR 24.8 7.1 6.4 8.1 1.58 CWR 25.2 7.0 6.4 2016-05-15
龙门对流云降水 CR 42.7 6.6 8.4 7.2 1.20 MRR 42.9 6.6 8.3 8.2 1.63 CWR 43.1 6.5 9.8
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表 3 2016年5月15日对流云降水过程中2.0 km，2.5 km，3.0 km，3.5 km，4.0 km高度处CR测得回波强度、CR逐库订正后回波强度、CWR测得回波强度对比
Table 3 Echo intensity detected by CR, CWR and corrected from CR at the height of 2.0 km, 2.5 km, 3.0 km, 3.5 km, 4.0 km in the convective cloud precipitation process on 15 May 2016
高度/km CR测得回波强度/dBZ CR订正后回波强度/dBZ CWR测得回波强度/dBZ 2.0 41.6 43.1 43.1 2.5 41.9 43.5 43.6 3.0 42.4 44.0 44.7 3.5 42.9 44.5 45.5 4.0 42.5 44.1 45.7
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表 4 2016年5月15日对流云降水过程中2.0~4.0 km高度每隔0.5 km的CWR回波强度差以及使用正演方法订正后的CR回波强度差
Table 4 Comparisons of echo intensity differences detected by CWR and echo intensity differences of CR corrected by direction deduce method at height of 2.0-4.0 km in the convective cloud precipitation process on 15 May 2016
高度 CR订正后回波
强度差/dBZCWR测得回波
强度差/dBZ2.0 km与2.5 km的差值 0.4 0.5 2.5 km与3.0 km的差值 0.5 1.1 3.0 km与3.5 km的差值 0.5 0.8 3.5 km与4.0 km的差值 -0.4 0.2
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