Analysis of lightning electromagnetic field propagation in mountainous terrain and its effects on ToA‐based lightning location systems
Analysis of lightning electromagnetic field propagation in mountainous terrain and its effects on ToA‐based lightning location systems
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DOI：
10.1002/2015jd024234
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发表时间：
2016-01
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通讯作者：
Dongshuai Li;M. Azadifar;F. Rachidi;M. Rubinstein;G. Diendorfer;K. Sheshyekani;Qilin Zhang;Zhenhui Wang
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文献类型：
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作者：
Dongshuai Li;M. Azadifar;F. Rachidi;M. Rubinstein;G. Diendorfer;K. Sheshyekani;Qilin Zhang;Zhenhui Wang
本文采用三维(3-D)时域有限差分(FDTD)方法，分析了闪电辐射电磁场在山区的传播效应。我们还具体讨论了目前用于探测网络中闪电定位的到达时间(TOA)技术中的时延误差。此外，对文献中提出的不同近似方法的精度进行了讨论，并用我们的三维FDTD方法进行了验证。结果表明：(1)山区地形及其绕射现象会显著影响闪电辐射电磁场的时延和幅值；(2)对于有限导体的地面，时间延迟随观测距离的增加而略有增加，但由有限的地面电导率引起的时间延迟似乎比山区地形引起的时间延迟小；(3)TOA技术的定时误差依赖于阈值时间。与对应于磁场的一阶导数的峰值的阈值时间相比，峰值的10%和20%的阈值时间提供非常相似的结果，并且阈值时间超过信号的初始上升幅度的50%。此外，我们还评估了两种简化方法(地形包络法和紧地形拟合法)在考虑山区地形传播引起的时间延迟方面的精度。结果表明，两种方法得到的时间延迟是合理一致的，但对于理想导电接地，用全波三维FDTD方法得到的结果总是被高估了。这两种方法代表了使用地形模型来解释非平坦地形上的时间延迟的有趣的替代方法。
In this paper, we analyze the propagation effects on lightning‐radiated electromagnetic fields over mountainous terrain by using a three‐dimensional (3‐D) finite difference time domain (FDTD) method. We also discuss the time delay error in the time‐of‐arrival (ToA) technique currently used to locate lightning in detection networks, specifically. Furthermore, the accuracy of different approximate methods presented in the literature is discussed and tested by using our 3‐D FDTD method. It is found that (1) the time delays and amplitudes of the lightning‐radiated electromagnetic fields can be significantly affected by the presence of a mountainous terrain and associated diffraction phenomena; (2) for a finitely conducting ground, the time delay shows a slight increase with the increase of the observation distance, but the time delay resulting from the finite ground conductivity appears to be smaller than that caused by the mountainous terrain; and (3) the timing error associated with the ToA technique depends on the threshold times. Threshold times of 10% and 20% of the peak provide very similar results compared to those corresponding to the peak of the first derivative of the magnetic field, and the threshold time exceeds 50% of the initial rising amplitude of the signal. Furthermore, we have assessed the accuracy of two simplified methods (terrain‐envelope method and tight‐terrain fit method) to account for the time delays resulting from the propagation in a mountainous terrain. It is found that both methods result in time delays that are in reasonable agreement but always overestimating the results obtained using the full‐wave 3‐D FDTD approach for the perfectly conducting ground. These two methods represent interesting alternatives to account for the time delay over a nonflat terrain using the terrain model.