中文摘要：

利用2012年青海大通地区高精度闪电三维辐射源定位结果和宽带电场脉冲波形同步数据,基于3种改进的传输线模型和粒子群优化算法,拟合发生在不同距离上不同类型闪电初始预击穿过程的双极性脉冲波形结构,反演初始流光通道内电流波形和特征参数,对比分析3种模型对初始预击穿过程和梯级先导双极性脉冲波形的拟合效果,统计分析4类闪电初始预击穿脉冲的物理特征。结果表明：3种改进的传输线模型均能较好地拟合出双极性脉冲结构,且MTLE模型更合理。负地闪的初始预击穿过程和梯级先导过程呈现出相同的传输特征,即均以梯级形式发展,且拟合物理参量也较为接近。初始流光向上的路径长度大于初始流光向下的路径长度,初始流光向上击穿进入上部正电荷区的路径上中和的总电荷量和总垂直偶极矩远大于初始流光向下的路径上中和的总电荷量和总垂直偶极矩。

英文摘要：

Physical characteristics of the initial breakdown pulse has been studied widely, but the exact three-dimensional position of the initial breakdown pulse and physical characteristics of the maximum amplitude initial breakdown pulse are not understood deeply yet. Based on three improved transmission line models and particle swarm optimization algorithm, the bipolar pulse of initial preliminary breakdown process in different types of lightning at different distances is fitted by using high-precision lightning three-dimensional radiation source localization results and synchronization data of wideband electric field pulse waveform at Datong of Qinghai. The radiation field component is modified and the current waveform of initial streamer channel and characteristic parameters are derived. The fitting effect of three models on the bipolar pulse waveform of the initial preliminary breakdown process and step leader process are comparatively analyzed, and the physical feature of the initial breakdown pulse are statistically analyzed. At the same time, the bipolar pulse propagation mechanism and physical characteristics of the lightning initial pro-breakdown process are further studied. All three models can reasonably fit the measured bipolar waveforms, and it may be more reasonable that the current in the channel exponentially decays with height. The leader process and the initial preliminary breakdown process of the negative cloud-to-ground flash show cascaded developing, and both parameters using MTLE model fitting is close, indicating their transmission features are similar. The total amount of charge, total vertical dipole moment and the path length of the initial streamer upward propaga- ting to positive charge region are larger than that of the initial streamer downward propagating to positive charge region. It may be related with the distance between the positive and negative charge region. When fitting the bipolar pulse waveform with three improved transmission line models, no model is constantly better than the