The Correction Method Of Ground Wave Delay And Its Application On Lightning Location Technology

Lightning is a common natural disaster,and its instantaneous large current and strong electromagnetic radiation can seriously endanger human life and human production and living activities.The research on wide-area lightning location can not only realize real-time detection and accurate location of lightning activity in China and the surrounding areas,but also have important applications in assessments of lightning hazard,thunderstorm monitoring and forecasting,satellite-based lightning detection and evaluation,and the study of transient luminous events when location results are combined with the lightning charge moment inversion method.In this paper,using 2D finite-difference time-domain methods and lightning location network data,the effects of real terrain on short distance lightning location are simulated,a new long range lightning location algorithm considering the influence factors such as real terrain along the propagation path is proposed and a new method of lightning impulse charge moment change(i CMC)inversion using measured ELF band data of fast electric field is proposed.The main contents and results are summarized as follows:(1)The effects of real terrain on lightning electromagnetic fields and lightning location accuracy are studied in two regions,Kunming,Yunnan and Fujian.The results indicate that the effect of real terrain on the lightning magnetic field is a combination of the enhancement effect of reflected waves at the junction of mountain and flat ground and the propagation attenuation due to the propagation path.The enhancement of real terrain on the lightning magnetic field in Fujian mountainous areas is greater compared with that in Kunming,which is related to the multiple superposition of reflected waves occurred in mountainous areas in Fujian.The peak arrival time is greatly affected by the real terrain,with a delay of 0.15 to 2.3μs in Kunming,and-0.2 to 2.2 μs in Fujian,while the 10% threshold arrival time is relatively less affected by the real terrain,with a delay of-0.11 to 0.92 μs in Kunming and-0.75 to 0.6μs in Fujian.In most cases,the lightning location error increases after considering the real terrain.The location error of the peak arrival time difference is the largest,in the order of kilometers,and that of the 10% threshold arrival time difference is the smallest in the order of hundreds of meters.but it is more likely to be affected by the real terrain,especially in the mountainous areas in Fujian.Relatively,using the arrival time difference obtained by cross correlation technique to locate lightning is an appropriate method.(2)A new algorithm for long range lightning location based on database identification of ground wave peaks combined with an equivalent propagation velocity is proposed,which equivalently replaces the influence factors such as real terrain along the propagation path on the lightning location.The detection efficiency and accuracy of very low frequency wide area lightning positioning network(VLF-LLN)were studied by selecting 5 thunderstorm cases and using the detection results of ADTD as reference.The results are as follows: The detection efficiency of VLF-LLN for 5 cases is between 40% and 80%,the average positioning error is between 2.73 km and 7.20 km.On the whole,the detection efficiency and accuracy of the thunderstorm case occurring in the south are higher,which may be related to the fact that most of the stations operating on that day are concentrated in the south.(3)A new method of lightning impulse charge moment inversion using measured ELF fast electric field is proposed.Firstly,the impulse response of the Earth-Ionospheric Waveguide(EIWG)for the ELF electromagnetic waves is simulated.Then,based on the similarity between the measured long range fast electric field waveform and impulse response,it is divided into two types.The propose inversion method is applied.in the weather process occurring in Xuzhou,Jiangsu Province on September 19,2021.When the fast electric field waveform and impulse response are similar,the i CMC can be directly obtained by comparing the measured ELF waveform with the simulated impulse response.When the fast electric field waveform and impulse response are not similar,the current moment is assumed to be the sum of two Heidler functions,and the unknown parameters in the reconstructed current moment are determined by using the genetic algorithm.The measured ELF waveform is consistent with the convolution of the simulated impulse response and the reconstructed current moment,indicating that the current moment is reasonable.The total charge moment change over the first 2 ms of the lightning stroke is i CMC.