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The Measurement Influence of Reflectivity Factor Caused by Scanning Mode from Phased Array Radar
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摘要: 有源数字阵列雷达的波束设计非常灵活，可变的波束宽度和多波束模式不仅可以满足不同任务的观测需求，还可有效节约扫描时间，但阵列天线参数随波位改变的特性对相控阵天气雷达回波强度的精确定标提出了挑战。2013年4—6月，中国气象科学研究院与安徽四创电子股份有限公司联合研发的X波段一维有源相控阵天气雷达 (X-PAR) 进行了装配后的首次测试观测。对比该雷达与相同位置的C波段双线偏振雷达 (C-POL) 观测资料发现，X-PAR不同宽度的扫描波束均能取得较合理的观测资料。但由于各模式的雷达方程及其标定方法不尽相同，并受到阵列天线照射体积、展宽波束和发射增益的影响，造成X-PAR回波强度存在一定的测量偏差。结合天线参数分析和实际数据统计将测量偏差订正至±1 dB内，为雷达的进一步调试和改进提供了依据。Abstract:
The beam design of active phased array weather radar is flexible, and this variable beam width and multi-beam mode can satisfy the requirement of various tasks and get much higher temporal resolution than general weather radar. However, the performance of active phased array weather radar can be hardly kept consistent due to the massive digital T/R components, and any variations of antenna parameters between the beam direction and axis normal would be a huge challenge for radar calibration. The X-band phased-array weather radar (X-PAR) developed by State Key Laboratory of Severe Weather of Chinese Academy of Meteorological Sciences and Anhui Sun-create Electronic Co Ltd is tested for the first time from April to June in 2013. The X-PAR and C-band polarization weather radar (C-POL) are installed at the same site, so their observations provide reflectivity measure deviation information and correction scheme for radar debugging and calibration of antenna parameters.During the operation of X-PAR, 3 kinds of observing modes with different beam width are applied, each using different parameters in their radar equations of calibration algorithm. Observations from C-POL and X-PAR (fine mode) with single scanning beam, X-PAR (quick mode) with multi scanning beams and X-PAR (fine Mode) are contrasted in detail. In order to reduce the comparison bias, severe convection and attenuation should be avoided. Results from statistical analysis indicate that observations from each elevation of X-PAR (fine mode) is 3 dB higher than C-POL, the measurement deviation between quick mode and fine mode changes along 4° regularly, and is inconsistent in higher elevation. The deviation source of X-PAR (fine mode) and C-POL comes from differences between the antenna parameter and the effective cross section, and the fast mode is also influenced by beam pattern, gaining in different elevation. A correction scheme based on data statistics and fitting is proposed to decrease the bias within 1 dB. By the comparison through vertical structures, the dependability of the above method is testified, and the resolution of X-PAR is also higher than C-POL, which is significant for convective precipitation research.The actual performance of phased array antenna could not keep strictly consistent with theoretical value because of its complicated structure. The result suggests that antenna measurement and digital T/R test during the factory inspection and acceptance are very indispensable. In the future field experiments, a well-calibrated radar should be installed at the same position to correct the X-PAR observation bias.
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图 1 X-PAR波位分布图
(a) 精细测量, (b) 警戒搜索, (c) 快速观测
Fig. 1 Beam distribution of X-PAR
(a) FM, (b) GM, (c) QM
图 2 X-PAR各仰角回波强度测量偏差随仰角变化廓线
(a) 精细测量与C-POL对比, (b) 快速观测与精细测量对比
Fig. 2 Reflectivity bias of X-PAR along elevation
(a) from FM to C-POL, (b) from QM to FM
图 3 波束剖面对比图
(a) X-PAR与C-POL的有效截面对比, (b) X-PAR快速观测模式收发波束分布图
Fig. 3 Comparison of beam profile
(a) effective cross section of X-PAR and C-POL, (b) transmitting and resaving beam positions of X-PAR QM
图 4 X-PAR快速观测与精细测量模式各仰角回波强度测量偏差随仰角变化廓线
(a) 快速观测模式经展宽波束订正, (b) 快速观测模式经过展宽波束和发射增益订正
Fig. 4 Reflectivity bias of X-PAR between QM and FM along elevation
(a) broaden beam correction for QM, (b) broaden beam and transmitting gain correction for QM
图 5 X-PAR与C-POL回波强度垂直剖面对比图
(a) X-PAR精细测量模式, (b) X-PAR快速观测模式, (c) C-POL
Fig. 5 Vertical cross sections comparison by X-PAR and C-POL
(a) FM, (b) QM, (c) C-POL
表 1 X-PAR 3种模式工作参数及波束特性
Table 1 Parameters and beam patterns of X-PAR (FM/QM/GM)
工作参数 精细测量 警戒搜索 快速观测 观测用时 (64点脉冲积累) 150 s, 90°方位 150 s, 360°方位 30 s, 360°方位 扫描策略 单波束顺序扫描 发射赋形波束14路接收 发射展宽波束4路接收 法向参数 φt0=0.61°, φr0=0.88°
Gt0=46 dB
Gr0=44.4 dBφt0不定, φr0=0.88°
Gt0不定, Gr0=44.4 dBφt0=4°, φr0=0.88°
Gt0=37.8 dB, Gr0=44.4 dB发射俯仰φt0 收发波束均以0.5°仰角的波位处开始, 以1°的步进角扫描至39.5° 赋形波束覆盖0°至20° 发射波束以2°仰角的波位处开始, 以4°为步进角扫描至38° 接收俯仰φr0 14路接收波束分布同VCP11 4路接收波束分布与精细测量模式一致 阵面夹角vt, vr vt=αt-10，vr=αt-10 vt=αt-10，vr=αt-10 vt=αt-10，vr=αt-10 接收增益Grv Grv=Gr0·cosvr 发射增益Gtv Gtv=Gt0·cosvt φt0=1.5°时约36 dB, 随仰角升高Gtv迅速减小, 在φt0=19.5°时约17 dB Gtv=Gt0·cosvt 波束宽度φv φv=φt0/cosvr φv=φr0/cosvr φv=φr0/cosvr 
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表 2 X波段相控阵天气雷达观测个例概况
Table 2 Weather observations of X-PAR
序号 日期 观测时段 雷达及观测模式 过程简单描述 1 2013-05-20 08:00—14:30 X-PAR (FM)，C-POL 较大范围对流及稳定降水 2 2013-05-21 09:00—19:00 X-PAR (FM)，C-POL 较大范围对流及稳定降水 3 2013-05-27 13:00—16:00 X-PAR (FM)，C-POL 较小范围对流 4 2013-05-28 19:00—20:00 X-PAR (FM/QM)，C-POL 较大范围稳定降水 5 2013-05-29 15:00—17:00 X-PAR (FM/QM)，C-POL 较大范围对流 6 2013-06-03 15:00—18:00 X-PAR (FM/QM)，C-POL 较小范围对流 7 2013-06-04 13:00—18:30 X-PAR (FM/QM)， 较大范围稳定降水 8 2013-06-05 13:30—17:30 X-PAR (FM/QM)，C-POL 较大范围对流 9 2013-06-10 13:00—18:00 X-PAR (FM/QM)，C-POL 中等范围稳定降水
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