地面瞬变电磁数据的早期畸变与校正方法

摘要

地面瞬变电磁勘探实践中发现,不同边长外框采集的数据在早期存在规律性畸变,推断关断时间和视电阻率转换算法均有可能引起畸变,为此采用试验方法进行验证.通过计算证实:实际关断时间并不足以引发电磁数据畸变;而在常规情况下的早晚期时间节点均存在数据畸变,且畸变主要发生在节点前,畸变程度与回线大小正相关;采用晚期公式计算是导致畸变的主要原因.使用二分搜索法对试验数据进行视电阻率转换,可以有效的克服电磁数据的早期畸变,获得与实际地层更吻合的视电阻率曲线.对不同外框试验数据的计算表明校正效果随外框边长的增大而减弱.%During the surface TEM prospecting practices,the early phase distortion can be found in data acquired from different sized loops have existed early phase regular distortions.It is inferred that the turn-off time and apparent resistivity conversion algorithm all can cause distortion,therefore,test procedure has been used to verify.Through computation has justified that the practical turn-off time is not enough to trigger electromagnetic data distortion.While under normal circumstances,early and late phase time nodes have data distortions,and mostly happened before the nodes;distortion degree is positively correlated with loop size;using late phase formula computation is the main reason to cause distortion.Through dichotomizing search carried out tested data apparent resistivity conversion,can effectively overcome early phase electromagnetic data distortion,obtained apparent resistivity curves are more accorded with actual strata.The computation of different sized loops tested data has shown that the calibrated effect is attenuating along with the increasing of loop size.