连绵起伏山体对雷电电磁信号的影响研究

Influences of the Mountainous Terrain on Lightning Electromagnetic Signal

连绵起伏的山体地形会对雷电电磁信号的强度和传播时间产生影响,进而影响到时间到达(time-of-arrival,TOA)雷电定位技术的准确性。本研究基于二维时域有限差分(two-dimensional finite-difference time-domain,2D FDTD)算法,对地闪回击电磁场在连绵山体地形的传播特征进行数值模拟,结果表明:1)连绵起伏山体的屏蔽作用和传播衰减对雷电信号强度的影响不可忽略。观测点附高山的静电屏蔽会引起垂直电场的显著削减。山体高度每增加500 m,山体传播衰减导致雷电信号的幅值平均下降约10%,不同观测点位置的衰减程度存在一定差异。2)连绵起伏的山体同时还会引起回击电磁场波形传播时间的变化。通过不同方法计算得到的到达时间结果存在较大差异,其中10%峰值、20%峰值以及最大导数点切线方法得到的结果相对接近。3)在2种路径延长的等效方法中,包络等效与上述3种计算方法得到的到达时间有很好的一致性,地表等效在山体较高时会对到达时间产生过高的估计。

The mountainous terrain affects the intensity and the arrival time of lightning electromagnetic signals,which in turn influences the accuracy of time-of-arrival( TOA) lightning location technique.A two-dimensional finite-difference time-domain(2D FDTD) algorithm is used to simulate the propagation of lightning electromagnetic signals along mountainous terrains. The results show that: 1) The influences of mountains,the shielding effect and propagation attenuation,cannot be ignored. The electrostatic shielding of the mountain causes a significant reduction on the vertical electric field nearby. For every 500 m increase in the height of the mountain,the attenuation causes the amplitude of the lightning signal to decrease by about 10% on average,and the attenuation has differences in different observation points. 2) The mountainous terrain will also affect the arrival time of lightning electromagnetic signals.The results calculated by different methods are quite different,and the results obtained by the 10%peak,20% peak and the linear extrapolation of the maximum field derivative methods are relatively close. 3) Among the two elongated propagation path methods,the terrain envelope method is in good agreement with the arrival time obtained by the above three calculation methods,while the tight-terrain-fit method may overestimate the arrival time when the mountain is high.