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Comparison on the Precipitation Measurement Between GPM/DPR and CINRAD Radars
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摘要: 通过对比星载DPR雷达与地基CINRAD雷达的降雨测量值，评估星地雷达联合应用的潜力。为了提高对比的准确性，在尽可能高的时空分辨率下，以几何匹配与格点匹配相结合的方式，提取星地雷达降水样本数据。2015年6月30日降水过程的对比分析结果表明：泰州、常州CINRAD雷达反射率因子在两站中分剖面的平均值偏差0.94 dB，地基雷达之间有很好的一致性；在DPR雷达与常州、泰州CINRAD雷达同时覆盖的降雨区域，星地之间雷达反射率因子的平均值偏差分别为-1.2 dB和-1.6 dB，显示星地雷达也有较好的一致性；现有DPR雷达陆上衰减订正算法在缩小星地雷达偏差方面起到一定作用，平均订正量0.4 dB，只要回波覆盖充分，匹配样本的高度以及其到地基雷达的距离对对比结果没有明显影响，而衰减订正和匹配样本区回波覆盖率是影响星地雷达对比结果的重要因素。Abstract: It is necessary to find out the difference between space-borne and ground-based radar data for evaluating the possibility of combined use of them. 2 neighboring ground-based radars at Taizhou and Changzhou are first checked for data consistence in full resolution and then compared with the DPR radar respectively. Results from the precipitation case on 30 June 2015 show that 2 radars have 0.94 dB bias of mean reflectivity factor on the profile where distances to both radars are equal.To get high temporal and spatial resolution comparisons between DPR and CINRAD, the geometry-matching algorithm is used in vertical where 1-14 DPR range gates could be included in one sample pairs according to the distance to CINRAD radar site. The further away it's from the radar site, the more DPR gates can be included. The grid-matching algorithm is used in horizontal where total 5×5 grids in 1 km resolution are matched with one single DPR range gate. The DPR and CINRAD volume-averaged values are calculated for all such intersecting DPR range gates and 5×5 CINRAD grids. Statistic results on sample pairs show that the mean reflectivity factor biases of DPR radar are -1.2 dB and -1.6 dB for CINRAD Taizhou and Changzhou radars, respectively, and the mean rain rate converted from Z-R relationship are 0.10 mm·h-1 and 0.13 mm·h-1 lower than CINRAD radars', over the same area where the three radars scanned successively within 6 min. When the distance to CINRAD gets longer, the bias between DPR and CINRAD is larger near the top of echo. And the bias in the bright band area is 122 dB larger than the mean bias as well. But the bias has no obvious relevance with distance and height in the other area if beam filling is enough.Attenuation correction and echo coverage over sample cell are among important factors which affect comparison results. Though there is no suitable surface reference, the attenuation correction algorithm for DPR radar over land works and decreases 0.4 dB in mean bias between DPR and CINRAD Taizhou. The maximum correction is only 1.36 dB due to moderate intensity of radar reflectivity factor.The equivalent radar reflectivity factor must be modified for the application of comparing DPR radar to other wavelength radar when the equivalent radar reflectivity factor is greater than 37 dBZ. For the application of combined multi-wavelength (such as DPR and CINRAD), data quality control and clutter identification and elimination are all among direct acting factors.
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Key words:
- GPM/DPR;
- CINRAD;
- reflectivity factor;
- rain rate
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图 2 泰州、常州雷达垂直平分线剖面反射率因子样本与仰角分布
(a)泰州、常州雷达垂直平分线剖面匹配样本平均值(点)与仰角关系，(b)3个仰角泰州、常州雷达垂直平分线剖面样本散点图和直方图
Fig. 2 Reflectivity factor of matched samples of CINRAD Taizhou and Changzhou on equal distance gates at different elevation angles
(a)comparison of matched sample means(dots) of CINRAD Taizhou and Changzhou on equal distance gates at all different elevation angles, (b)marginal histogram of matched samples(dots) of CINRAD Taizhou and Changzhou on equal distance gates at three different elevation angles
图 3 泰州、常州雷达垂直平分线剖面反射率因子样本与斜距分布
(a)泰州、常州雷达垂直平分线剖面匹配样本平均值(点)与斜距关系，(b)3个斜距泰州、常州雷达垂直平分线剖面样本散点图和直方图
Fig. 3 Reflectivity factor of matched samples of CINRAD Taizhou and Changzhou on equal distance gates at different range section
(a)comparison of matched sample means(dots) of CINRAD Taizhou and Changzhou on equal distance gates at different range section, (b)marginal histogram of matched samples(dots) of CINRAD Taizhou and Changzhou on equal distance gates at three different range section
图 4 星地雷达反射率因子廓线(a)及反射率因子差廓线(b)
Fig. 4 Radar reflectivity factor Z profiles(a) and radar reflectivity factor difference profiles(b) of DPR and CINRAD
图 5 DPR与常州雷达匹配样本量随距离分布
Fig. 5 Distribution of the number of sample pairs(DPR and CINRAD Changzhou) along range
图 6 DPR与常州雷达反射率因子差随距离分布
Fig. 6 Distribution of Z difference between DPR and CINRAD Changzhou along range
图 7 5000 m以上高度DPR雷达与常州雷达反射率因子差随距离分布
Fig. 7 Distribution of Z difference between DPR and CINRAD Changzhou above 5000 m along range
图 8 DPR雷达衰减订正前后Z值垂直分布
Fig. 8 Z profiles of DPR before and after attenuation correction
图 9 DPR雷达跨轨道(左侧)和沿轨道(右侧)回波剖面(左侧x轴0对应星下点，右侧x轴为星下点纬度)
(a)右侧为11号射线沿轨道测量回波剖面，(b)右侧为16号射线沿轨道测量回波剖面，(c)右侧为16号射线沿轨道杂波处理后的回波剖面
Fig. 9 DPR echo profile cross track(left) and along track(right) over China(zero of the left x axis denotes satellite nadir, the number of the right x axis is latitude of satellite nadir)
(a)the ray 11 of measured Z along track, (b)the ray 16 of measured Z along track, (c)the ray 16 of processed Z by quality control
图 10 不同温度下Mf和降水强度的关系(a)μ=0，(b)μ=2
Fig. 10 Mf vs rain rate at different temperature with μ=0(a) and μ=2(b)
图 11 不同温度下频率修正因子Mf与Ku波段等效反射率因子ZeKu关系
Fig. 11 Mf vs equivalent reflectivity factor ZeKu
表 1 DPR雷达与泰州和常州雷达探测结果统计
Table 1 Comparison of reflectivity factor and rain rate between DPR and CINRAD
雷达名称 平均覆盖率/% 平均距离/km Z平均值/dBZ Z最大值/dBZ 平均降水强度/(mm·h-1) DPRCZ 94 46.1 23.6 35.5 0.97 常州 82 46.1 24.8 35.5 1.07 DPRTZ 91 54.7 23.5 34.1 0.95 泰州 82 54.7 25.1 39.1 1.08 
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