C波段调频连续波天气雷达探测系统及观测试验

The C-band FMCW pointing weather radar system and its observation experiment

中文关键词:  C波段调频连续波天气雷达  定量标校  数据比对  降水云探测

英文关键词:C  band  frequency  modulation  continuous  wave  (FMCW)  radar,  Radar  quantitative  calibration,  Reflectivity  comparison  analysis,Precipitation  cloud  detection  capability

中文摘要:

      对降水云更高时、空分辨率观测资料的需求推动了天气雷达技术的发展,调频连续波雷达(FMCW)系统采用收发分置双天线体制,采用数字直接移相(DDS)技术和快速傅里叶变换(FFT)信号处理技术,获取高度分辨率达到15、30 m,探测周期2—3 s的回波功率谱分布和谱参数,具有脉冲多普勒雷达无法比拟的探测优势。C波段FMCW(C-FMCW)雷达最小可测信号功率达到-170 dBm,微弱信号的定量标校是技术难点。采用标准信号源输出单频信号,经过数字直接移相扩展为与雷达系统相同扫频范围信号,得到最小输入功率可达-169.77 dBm的定标曲线,由定量标校后的谱分布计算得到回波强度谱密度分布。该雷达于2013年6月起在安徽定远开始观测,利用8月24日降水过程探测数据,与距离该地48 km的蚌埠和83 km的合肥SA扫描雷达观测数据,分别进行对流云与层状云的观测比对分析。对于均匀分布的层状降水云,C-FMCW雷达与SA雷达探测结果基本接近, C-FMCW雷达与蚌埠SA雷达的平均均方根误差为1.75 dB,与合肥SA雷达的平均均方根误差为2.02 dB,C-FMCW雷达与两部SA雷达探测的回波强度差异小于1 dB。对观测试验谱参数及回波强度谱密度分布进行了初步分析,C-FMCW雷达在研究降水云体的相态分区、晴空大气边界层回波等方面有较好的应用前景,有助于加深对强降水云中垂直运动的强烈变化的探测和认识。

英文摘要:

      The C-band Frequency Modulation Continuous Wave (C-FMCW) vertically pointing radar was developed with a newly signal processing technology. The C-FMCW radar uses the two-dimensional FFT signal processing technology, with the lowest detectable echo power of -170 dBm, and the quantitative calibration is difficult for weak signal. For a standard signal source analog echo point frequency, its frequency signal is able to be broadened to the signal with the same scanning range as the radar system, to get the calibration curve with the minimum input power up to -169.77 dBm, in which the calibration curve inflection point is able to confirm that the radar noise power is about -168 dBm. The spectral density of reflectivity can be computed from the spectrum of quantitative calibration. The data observed from the C-FMCW radar are compared with the SA scanning radar on Dingyuan, Anhui Province from June of 2013. The comparison analysis uses the data from the 48 km and 83 km CINRAD/SA Bengbu and Hefei radar, respectively, for the August 24 precipitation event. This event includes the two stages with convective cloud and stratiform cloud respectively. The reflectivity vertical distributions in the stratiform cloud for the C-FMCW radar and CINRAD/SA weather radar are basically in agreement, showing that the calculation of the C-FMCW radar system is reasonable. The average difference between the C-FMCW radar and SA radar in Bengbu in terms of the root mean square difference is 1.75 dB, and that between it and the Hefei SA radar is 2.02 dB. A preliminary analysis using the products and the spectral density of reflectivity, shows that the C-FMCW radar has a good prospect in the identification for the different particle phase thickness in precipitation cloud body, the study of echoes in the boundary layer of the clear atmosphere. And, it can also help to recognize the strong variations of vertical motion in the severe rain clouds.