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摘要
Short-offset grounded-wire transient electromagnetic method (SOTEM) has considerably improved the signal intensity by using the form of near-source detection. The present researches on SOTEM responses are mainly based on ID models and explore the response characteristics and detection abilities of two components: electric field Exand magnetic field Hzwhich are not conducive to the accurate exploration of complex targets. Based on the above-mentioned problems, a three-dimensional (3D) finite-difference time-domain (FDTD) was employed to simulate the diffusion pattern of SOTEM field in strata and the influence of 3D anomalous body on the diffusion of SOTEM field. The results show that the positive extreme value area of electric field Excomponent mainly appears nearby the transmitting source, and diffuses gradually downward with time; the positive extreme value area and negative extreme value area of electric field Eycomponent are mainly located at two ends of the transmitting source, and diffuse gradually downward and outward with time; the electric field Ez component undergoes jump at strata boundary; the positive extreme value area and negative extreme value area of magnetic field H2 component are respectively located at two ends of the transmitting source, and diffuse gradually downward and outward with time; the upper part and lower part of magnetic field Hy component are negative value area and positive value area, respectively, indicating that Hy component will also be affected by the return current; the extreme value area of magnetic field H, component is mainly below the transmitting source, and gradually moves downward with time; for the 3D anomalous body, the sensitivity areas of electric field Exand magnetic field Hy components are rightly above the anomalous body, while the sensitivity areas of electric field Ey and magnetic field Hzcomponents are outside the anomalous body and distribute around it, and the sensitivity areas of magnetic field Hzcomponent are on both sides of the anomalous body (close to transmitting source, and distant from transmitting source, respectively). It shows that the five components of SOTEM field have different sensitivity areas to the 3D anomalous body, and different components should be observed in different areas.
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