| Ground flashback strikes can generate a wide-band electromagnetic field,but the electromagnetic wave will be affected by the ground conductivity and uneven terrain when it propagates,causing the peak and rising edge time of the waveform to change.Most of the existing lightning location and lightning current parameter inversion algorithms assume that lightning electromagnetic waves propagate along a smooth ideal surface.Under some complex terrain conditions,lightning location and current parameter inversion will have certain errors.The thesis first established an FDTD mountain model in a simple two-dimensional cylindrical coordinate system,and discussed the influence of mountains at different positions on the propagation path on lightning electromagnetic waves.According to the lightning location network deployed in Kunming,Yunnan,the 2°×2° study area was equally divided into 100 grid points,and a lightning bolt was simulated at the center of the grid point,and a two-dimensional FDTD model under real terrain was further established.Based on the simulation results,the influence of mountainous terrain on the peak value of the vertical electric field is analyzed,and the correction effect of the non-synchronously long terrain envelope method on the lightning location error is studied.The main conclusions are as follows:(1)Isolated mountains at different locations on the propagation path have different effects on lightning electromagnetic waves.When lightning strikes the top of the mountain,the peak value of the electromagnetic field waveform will increase compared to flat ground.With the slope width unchanged,the increment will gradually increase with the increase of the inclination of the mountain,but the growth rate will gradually decrease.The installation of the measuring station on the top of the mountain can also cause an increase in the peak value of the electromagnetic wave signal.With the increase of the inclination of the mountain,the increment gradually increases,but the growth rate gradually decreases.In addition,the mountain between the lightning strike and the station will cause the attenuation of the peak lightning electromagnetic wave received by the station.The attenuation effect of the mountain 5km away from the lightning strike point or the measuring station on the lightning electromagnetic wave is similar,and it is greater than the attenuation caused by the mountain at the center of the path.When the slope width is constant,the greater the slope of the mountain,the stronger the attenuation.(2)The influence of mountainous terrain on the peak value of the lightning vertical electric field waveform is very complicated.According to the different influences of mountains at different locations on the peak electric field,this paper proposes the peak influence factors related to the location and height of the mountain.The approximate expression of the peak ratio of the vertical electric field when the lightning electromagnetic wave propagates in the mountainous terrain of Kunming to the peak value of the vertical electric field when propagating on the flat ground is given.Fitting 257 vertical electric field waveforms with a propagation distance between 100 km and 200 km obtained by simulation,the optimal solution of the influence factor is given.The peak ratio error is 0.0131 and the standard deviation is0.0995.(3)Different waveform time arrival algorithms produce different lightning location error results.Among them,the 10% peak method has a better location effect than the waveform crosscorrelation method and the peak method.The non-synchronously long terrain envelope method has a certain effect of correcting the lightning positioning error,and the global envelope method has the best effect.The global envelope method was used to correct the regional lightning positioning errors under the three waveform time arrival algorithms.As a result,nearly twothirds of the lightning was successfully corrected.In addition,the value of the envelope length of the global envelope method divided by the speed of light is very close to the waveform arrival time obtained by the 10% peak method.Therefore,this paper proposes that the lightning positioning accuracy of the station area can be quickly obtained by the global envelope method. |
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