Affiliation:
1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences , Beijing 100029 , China
2. Innovation Academy for Earth Science, Chinese Academy of Sciences , Beijing 100029 , China
3. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences , Beijing 100049 , China
Abstract
AbstractIn artificial-source electromagnetic explorations, the shadow effects and source overprint effects are two of the key factors to affect the detection reliability. Compared with frequency-domain electromagnetic methods, the transient electromagnetic (TEM) shadow effect and source overprint effect are more complex, especially for the short-offset TEM (SOTEM) observed in the near-source region. However, there is less relevant research. Therefore, in this paper, we first realize 3D SOTEM simulations based on the vector time-domain finite element method, then further analyze the generation of SOTEM shadow effect and source overprint effect from view of the diffused electromagnetic fields, as well as their influence on ground horizontal electric field Ex and vertical induced voltage dBz/dt responses. Results show that the attraction or repulsion of the electrical inhomogeneity would affect the diffusion speed of the electromagnetic fields, which is the essential in the two source effects. Besides, from view of the ground Ex and dBz/dt responses, the relative anomaly of SOTEM shadow effect is almost twice those of the SOTEM source overprint effect, i.e. the SOTEM shadow effect is easier to record, especially for dBz/dt responses. In addition, owing to the shadow effect, SOTEM may fail to identify the real target anomaly, whereas the influence of the source overprint effect for recognizing the target anomaly mainly occurs on all-time dBz/dt responses and early-time Ex responses (before about 10 ms), that is, observing late-time SOTEM Ex responses can effectively avoid such influence. Hence, to fully ensure avoiding the influence of the source overprint effect, we suggest adopting high-power transmission to increase the late-time signal-to-noise ratio in field measurements.
Funder
National Natural Science Foundation of China
National Key Research and Development Program of China
Institute of Coal Geology Planning Survey of Shandong Province
Publisher
Oxford University Press (OUP)
Subject
Management, Monitoring, Policy and Law,Industrial and Manufacturing Engineering,Geology,Geophysics
Cited by
1 articles.
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1. Advances in transient electromagnetic methods;Journal of Geophysics and Engineering;2023-10-25