Wavelet Analysis Processing And Electrical Layer Division For Transient Electromagnetic Data

Transient electromagnetic method, as a geophysical method, detects geological underground targets by electromagnetic induction. Refer to properties of less effect caused by terrain, greater depth of detection, stronger ability for penetrating the high impedance layer and higher work efficiency, it become one of the important methods for mid-shallow exploration. But for the preprocessing of transient electromagnetic data and corresponding vertical electrical layering, there remain some questions need to discuss due to complexity of geologic setting.The wavelet analysis, which was known as'mathematical microscope', emerged in the field of signal analysis and processing in recent years. It aims at non-stationary processing, so it is applicable to detect and show the components of transient anomalies entrained in normal signal, especially for dynamic and transient signal processing. Because of the signal obtained from transient electromagnetic method is exactly dynamic and transient, it becomes feasible to apply wavelet analysis for signal processing, in order to achieve the purpose of improving interpretation accuracy. Transient electromagnetic method is more applicable to detect a conductor underground, while for high resistivity bodies, especially to differentiate vertical electrical layer in such section, corresponding research has not attract enough attention. In this paper, wavelet transform is used for filtering data which was derived from detecting in the field, and then slope filtering applied to induced voltage attenuation curve according to late response law of transient electromagnetic. And in the premise of ensuring data original trend, smoother induced voltage attenuation curve can be obtained. At last, based on the effect of signal preprocessing, it believe that in the primary data, the corresponding data after the first variational point which has major amplitude on the curve should be abandon rather than participation as a normal response to the magnetic field inversion and interpretation.Apparent resistivity curveρτ(t) is commonly used in the transient electromagnetic data inversion and interpretation, but apparent vertical conductance parameter curve sτ(t) is seldom used, it mainly be applied to interpretation for conductor. In this paper, apparent vertical conductance parameter curve sτ(t) is used to deal with data in detail interpretation and processing, on account of the given target which is a high resistivity body. Then vertical with horizontal resolution comparison is followed. Finally, it discusses advantages and limitations of horizontal and vertical electrical resolution by using the two curves. The experiment shows that it is feasible to use apparent vertical conductance curve divides vertical strata electrical layer, and it has important practical significance for studying curve subtle changes in case of solving practical problems.