3-D inversion of transient EM data with topography using unstructured tetrahedral grids

Liu, Yunhe; Yin, Changchun; Qiu, Changkai; Hui, Zhejian; Zhang, Bo; Ren, Xiuyan; Weng, Aihua

doi:10.1093/gji/ggz014

Cited by 57 publications

(15 citation statements)

References 34 publications

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“…The implicit scheme is based on solving Equation (2). In order to improve the accuracy, the second-order backward Euler method is used to discretize time derivatives [4], e.g., ∂e ∂t is approximated as:…”

Section: Implicit Scheme Using the Backward Euler Methodsmentioning

confidence: 99%

“…The TEM forward modeling can be implemented in frequency-domain and thereafter transformed to time-domain using the Fourier transform. However, the frequency-domain approach generally requires a sufficiently dense and wide frequency range to ensure the accuracy of the solution [4]. Alternatively, the simulation can be implemented directly in the time-domain so that the electromagnetic (EM) fields are recursively advanced using time-stepping [5].…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the horizontal grid resolution can be coarser with depth. Several approaches with variable model discretization were proposed, e.g., Octree grid [14,15], unstructured grid discretized by the tetrahedral cells [4,10] for the finite-element method modeling, etc. Our previous study developed the Multi-Resolution (MR) gird approach, which has been initially implemented in the 3-D magnetotelluric forward modeling [16] and extended to the direct current resistivity method [17] and TEM method using the explicit scheme [18].…”

Section: Introductionmentioning

confidence: 99%

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A Comparison Study of Explicit and Implicit 3-D Transient Electromagnetic Forward Modeling Schemes on Multi-Resolution Grid

et al. 2021

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This study compares the efficiency of 3-D transient electromagnetic forward modeling schemes on the multi-resolution grid for various modeling scenarios. We developed time-domain finite-difference modeling based on the explicit scheme earlier. In this work, we additionally implement 3-D transient electromagnetic forward modeling using the backward Euler implicit scheme. The iterative solver is used for solving the system of equations and requires a proper initial guess that has significant effect on the convergence. The standard approach usually employs the solution of a previous time step as an initial guess, which might be too conservative. Instead, we test various initial guesses based on the linear extrapolation or linear combination of the solutions from several previous steps. We build up the implicit scheme forward modeling on the multi-resolution grid, which allows for the adjustment of the horizontal resolution with depth, hence improving the performance of the forward operator. Synthetic examples show the implicit scheme forward modeling using the linearly combined initial guess estimate on the multi-resolution grid additionally reduces the run time compared to the standard initial guess approach. The result of comparison between the implicit scheme developed here with the previously developed explicit scheme shows that the explicit scheme modeling is more efficient for more conductive background models often found in environmental studies. However, the implicit scheme modeling is more suitable for the simulation with highly resistive background models, usually occurring in mineral exploration scenarios. Thus, the inverse problem can be solved using more efficient forward solution depending on the modeling setup and background resistivity.

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Section: Implicit Scheme Using the Backward Euler Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Comparison Study of Explicit and Implicit 3-D Transient Electromagnetic Forward Modeling Schemes on Multi-Resolution Grid

et al. 2021

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“…At present, the numerical simulation methods for 3D electromagnetic method mainly include the integral equation method (Wannamaker et al ., 1984; Zhdanov et al ., 2006), the finite‐difference method (Commer & Newman, 2004; Yu et al., 2017), the finite volume (FV) method (Weiss & Constable, 2006; Haber et al ., 2007a) and the finite element (FE) method (Key & Ovall, 2011; Sliva et al ., 2012; Cai et al ., 2014). Compared with other methods, the FE method with an unstructured mesh can provide accurate results for complex geological models with topography (Liu et al ., 2019). The FE method usually results in a large linear system of equations in the forward modelling, which can be difficult/time intensive to solve.…”

Section: Introductionmentioning

confidence: 99%

Three‐dimensional inversion of semi‐airborne transient electromagnetic data based on finite element method

Hao

Cai

Liu

et al. 2022

Near Surface Geophysics

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The semi-airborne transient electromagnetic method is characterized by a large detection depth, high signal-to-noise ratio, fast acquisition rate, low cost, and ability to be used for exploration in scenarios with complex geological conditions. As a result, the semi-airborne transient electromagnetic method has a great potential in the fields of mineral exploration, hydrological study and geohazard detection. However, most of the existing semi-airborne transient electromagnetic data interpretation methods still rely on one-dimensional forward modelling and inversion, which could lead to an incorrect geological interpretation. In this paper, we develop a three-dimensional inversion for semi-airborne transient electromagnetic data to recover a reliable subsurface conductivity distribution. The forward modelling is based on the effective vector finite element method with an unstructured tetrahedral mesh, which is capable of simulating complex geo-electric structures and the topography. Through the numerical experiments of several three-dimensional synthetic models, we study the influence of the number of excitation sources, flight mode and complex topography on the inversion results. The synthetic model studies reveal that: (1) by increasing the number of excitation sources, we can obtain a higher resolution conductivity image with less artefacts; (2) the detectability can be increased by flying along the terrain when the topography is complex; (3) the topography should be considered in the forward modelling and inversion to obtain a reasonable conductivity model using the semi-airborne transient electromagnetic method; and (4) the three-dimensional inversion still works when the inhomogeneity is present nearby the transmitter.

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“…Although the free space between the topography and the airborne draping surface or the satellite observation surface is not contained within the inverse model, it still needs to be considered in forward modeling, which inevitably increases the cost of forward modeling. Considering relevant existing research on other geophysical methods, such as electromagnetic (EM) (Liu et al, 2019;Rücker 2006aRücker , 2006bUsui, 2015) and seismic techniques (Dumbser & Käser, 2006), unstructured tetrahedral grids exhibit good performance in the modeling of complex topography, and geometries at arbitrary resolutions, and high accuracy in the interpretation of inversion results (Darijani et al, 2021;Lelièvre & Farquharson, 2013). Therefore, in this study, we propose that the abovementioned challenges should be addressed by developing 3-D magnetic data numerical forward modeling and inversion methods with an unstructured tetrahedral grid.…”

mentioning

confidence: 99%

3‐D Magnetic Unstructured Inversion

et al. 2021

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3-D inversion of transient EM data with topography using unstructured tetrahedral grids

Cited by 57 publications

References 34 publications

A Comparison Study of Explicit and Implicit 3-D Transient Electromagnetic Forward Modeling Schemes on Multi-Resolution Grid

A Comparison Study of Explicit and Implicit 3-D Transient Electromagnetic Forward Modeling Schemes on Multi-Resolution Grid

Three‐dimensional inversion of semi‐airborne transient electromagnetic data based on finite element method

3‐D Magnetic Unstructured Inversion

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