地面电导率、地球曲率和电离层对远距离闪电定位的影响

Influences of Ground Conductivity, Earth Curvature and Ionosphere on Long-Distance Lightning Locating

为了研究地面电导率、地球曲率和电离层对远距离(大于200 km)闪电定位的影响,通过新型近似算法和二维时域有限差分(two-dimensional finite-difference time-domain, 2D-FDTD)算法进行数值模拟,分析雷电电磁场的远距离传播特征,并采用“时差法”(time-of-arrival, TOA)进行远距离闪电定位。结果表明:1)雷电电磁场沿陆地表面传播时,受地面电导率、地球曲率影响,距离每增加100 km,峰值到达时间平均延后1.24μs,分别带来482 m和976 m的定位误差(小于0.5%);2)电离层会引入天波信号。观测距离大于700 km时,地波难以识别,会误把天波峰值时刻当作峰值到达时间,导致定位错误,甚至无法定位;3)识别地波后,定位误差仅为504 m。因此,在进行远距离闪电定位前,必须先进行地波识别,再利用地波进行定位。研究结论对提高远距离闪电定位精度有科学意义,对雷电预警具有实际的参考价值。

In order to study the influence of ground conductivity, earth curvature and ionosphere on long-distance(more than 200 km) lightning locating, numerical simulation is carried out by a new approximation algorithm and a two-dimensional finite-difference time-domain(2 D-FDTD) algorithm to analyze the long-distance propagation characteristics of the lightning electromagnetic field, and the time-of-arrival(TOA) lightning location technique is used for long-distance lightning locating. The results show that: 1)When the lightning electromagnetic field propagates along the land surface, due to the influence of the ground conductivity and the earth curvature, the propagation distance increases by 100 km, and the peak arrival time is delayed by an average of 1.24 μs. The positioning errors caused by the two are 482 m and 976 m, which are less than 0.5%. 2) The ionosphere adds sky wave signals to the long-distance lightning electromagnetic field waveform. When the observation distance is greater than 700 km, the ground wave is difficult to identify, so the time when the peak of the sky wave arrives is mistakenly regarded as the peak arrival time, resulting in a wrong locating result and even unable to locate. 3) After artificially identifying ground waves and eliminating the influence of sky waves, the long-distance lightning locating error is only 504 m. Therefore, before long-distance lightning locating, the ground wave must be identified first and then the identified ground wave shall be used to locate. The research conclusions have scientific significance for improving the long-distance lightning locating accuracy, and have practical reference value for lightning warning.