斜阶跃波层状介质航空瞬变电磁响应数值计算

目前,航空瞬变电磁方法数据解释主要采用阶跃波均匀半空间模型计算视电导率值,而实际航空电磁系统发射波形的下降沿多为斜阶跃,导致解释时计算的视电导率值存在较大偏差。为此,笔者研究了航空瞬变电磁系统发射电流为斜阶跃时的电磁响应数值计算,将发射波形进行拉氏变换,利用G-S逆拉氏变换与241点汉克尔变换相结合的方法,实现斜阶跃波关断后的层状大地模型航空瞬变电磁响应计算;并对均匀半空间和层状大地模型下,不同关断时间和不同飞行高度对电磁响应的影响进行分析。得出结论:不同关断时间,关断后取样延时2 ms时,均匀半空间电磁响应的平均偏差为27.78%,三层模型的平均偏差为32.16%;当飞行高度从20 m增加到60 m时,均匀半空间和三层模型的感应电动势分别减小了43.6%和83.2%。

Numerical Calculation of Layered Media of Ramp Step Wave on Airborne Transient Electromagnetic Response

The apparent conductivity was was usually calculated by half homogeneous space step wave model for the data interpretation of airborne transient electromagnetic method(ATEM).However,the falling edge of transmitted waveform of actual airborne electromagnetic system is a ramp function,which leads to a large deviation in calculation of apparent conductivity.The authors studied the numerical calculation of electromagnetic response for the ramp function by Laplace transformation,combined with the integration of G-S Laplace inverse transform and the 241 points Hankel Transform,to calculate the ATEM numerical computation of the layered earth model after switch-off time,and analyzed the influence of electromagnetic response in the different switch-off time and flying altitude under the half homogeneous space and layered earth model.The results showed that the mean deviation of the electromagnetic response of half homogeneous space is 27.78% and of 3 layered model is 32.16% in the 2 ms delay for different switch-off time.When the flying altitude tripled,the induced value of the uniform half space and 3 layered earth model reduces 43.6% and 83.2%,respectively.