中文摘要：

基于电偶极子在水平多层土壤上方的频域辐射磁场计算公式，得出了任意水平多层土壤上方雷电流辐射磁场的时域计算公式。以水平两层土壤为例，考虑上层土壤的不同厚度和上、下层土壤电导率的变化，从时域和频域两方面分析了水平分层土壤模型对雷电辐射场的影响。结果表明，在上层土壤电导率大于下层土壤电导率的情况下，上升时间内的雷电辐射磁场强度均小于同时刻土壤参数全部为上层土壤时的结果，并且大于土壤参数全部为下层土壤时的结果；当上层土壤电导率小于下层土壤电导率时，上层土壤厚度较小时其结果接近全部为下层土壤时的相应结果；但是随着上层土壤厚度的增加，雷电辐射磁场最大值将大于全部为上层土壤或全部为下层土壤时的计算结果，且随着上层土壤厚度的增加而最终接近全部为上层土壤时的计算结果。最后对雨季这一典型气候条件下的雷电辐射场做了特别分析，由于降雨的影响，地表土壤电导率增加，使得测点的雷电辐射磁场上升时间减小，但是相应峰值所受影响较小。因此在实际的雷电监测中，由雷电辐射磁场强度反演雷电流峰值时可以不考虑降雨造成的土壤电导率变化。

英文摘要：

Based on the frequency-domain expression of the magnetic field radiated from the dipole over horizontallystratified ground, the general formula was proposed to calculate the lightning radiation magnetic field above lossy ground stratified with any number of horizontal layers. Taking the two-horizontal-layer soil as example, the effect of the stratified soil on the lightning radiation field in time and frequency domain was investigated. Different thickness of the upper layer and the conductivity changes of the two soil layers were both taken into account. The results indicate that, when the conductivity of the upper layer is larger than the lower, the lighting radiation magnetic field within the rise time is less than that above the homogeneous soil characterized by the upper layer, and larger than that above homogeneous soil with the conductivity equal to lower layer. For the case the conductivity of the lower layer is larger, the calculated lightning radiation field is almost identical with the radiation field above homogeneous ground composed of the lower soil layer, when the upper layer is of little thickness. But with the increase of the upper layer thickness, the maximum lightning radiation magnetic field may exceed the radiation magnetic field above homogeneous ground characterized with the upper or lower soil layer, and ultimately tend to agree with the result obtained when the upper soil layer is of finite thickness. During rainy season, due to the increase of the ground surface conductivity resulted from the rainfall, the observed rise time of the lightning radiation magnetic field decreases accordingly. While the peak value of the lightning radiation magnetic field is influenced slightly. Therefore, in the inversion of the lightning current peak value from the lightning radiation magnetic field, the change of soil conductivity resulted from the rainfall can be neglected.