激励信号对地-空瞬变电磁响应的影响分析

Analysis of excitation signal effect on grounded electrical-source airborne transient electromagnetic response

运用数字滤波法和辛普森积分法,计算了阶跃波层状大地地-空瞬变电磁响应;以此为基础,通过卷积方法可得任意激励波形的电磁响应。从激励信号能量角度分析了激励波形的响应,能量大对应的响应就大。通过正演计算,半正弦波和三角波在on-time段响应随电导率的变化不明显;而off-time段高阻异常很快进入噪声区,在数据解释时,无法得到足够多的有用信息。为了解决这一问题,发射波形采用梯形波或方波,同时记录on-time段和off-time段数据进行异常分析,可使反演分辨率更高。

We calculated the grounded electrical-source airborne transient electro- magnetic response of step wave in the layered earth, using digital filter and Simpson integration method. Based on these obtained values from step wave response, the e- lectromagnetic response of arbitrary excitation wave can be extracted by convolu- tion. We analyzed the response by excitation energy. The higher the excitation en- ergy is, the larger the response is. During the forward calculation, with different conductivities, no significant changes of the responses of half sine wave and trian- gular wave have been observed in the on-time zone. At the same time, high resist- ance target quickly enters the noisy area in the off-time zone. It is impossible to re- trieve enough information. To solve this problem, the transmitter current adapts the trapezoidal wave or square wave. We have managed to record the processes for both the on-time and off-time zones simultaneously. We use it to analyze the anom- aly, which makes the resolution of inversion higher.