瞬变电磁中两种发射源的响应特征研究

Study on TEM response characteristics of two kinds of transmitter sources

大回线源作为一种快速有效的瞬变电磁观测方式,它的优点是铺设一次线框,在框内和框外都可以测量,空间采样率高、工作效率高和解释精度高,特别适合高密度、大深度的面积测量。目前针对矩形源计算有两种方式,1通过面积等效法用圆形发射源代替矩形发射源;2利用水平偶极子沿矩形回线做数值积分。这里计算了两种发射装置内二次场值,研究两种发射源内二次场的分布特征,证明对于中心回线装置、大定源装置,在晚期使用面积等效方法用圆型线框代替矩型线框计算视电阻率是有效的,在早期计算会引入较大误差,需要校正。

Large-loop source as a quick and efficient observation way of transient electromagnetic,it has the advantage of laying a wireframe,outside and inside the box being measured,high spatial sampling rate,high work efficiency and interpreta-tion accuracy,especially suitable for the area survey of high density and big depth.At the moment,there are two calculation ways for rectangular source.The first is using circular transmitter source instead of rectangular transmitter source;The second is using a horizontal dipole along the rectangular loop for numerical integration.This paper calculate the secondary field value within two transmitters loop,study the distribution characteristics of secondary field of two kinds source in the loop,proved that for the central loop device and large fixed source device.The method that using a circular transmitter wireframe instead of rectangular transmitter wireframe to calculate the apparent resistivity in the later period is effective,calculation the early appar-ent resistivity will introduce greater error and needs correction.