Bo Zhang

• Doctor of Engineering
• 938 Ximinzhu Str. Changchun, Jilin,China at Jilin University

When using electrical prospecting methods to monitor the front edge of waterflooding in the residual oil development, the electromagnetic responses generated by the high conductivity of the steel casing in the observation area usually obscure the electrical abnormal signal of the formation caused by waterflooding, largely affecting the imaging accu...

Bauxite plays a crucial role in metallic and non-metallic industry. The surface-exposed salento-type bauxite deposits have been largely exploited and developed. With the increasing demand of these resources, it is important but very challenging to explore the potential bauxite deposits in the deep earth. In this paper, based on new developments in...

Localized water-rich areas in aquifers can cause severe accidents during coal mining, including property damage and casualties. Traditional ground-based geophysical methods often struggle in the mountainous terrains where coal mines are typically located. To address this, we applied a high-resolution exploration and interpretation strategy based on...

As the structure of the underground space becomes increasingly complex, traditional two-dimensional seismoelectric methods are no longer adequate for the comprehensive exploration. To achieve precise imaging of the underground space, it is in urgent need to develop three-dimensional full-waveform modeling techniques. In this paper, we propose a thr...

Airborne electromagnetic (AEM) technology is an efficient geophysical exploration tool for investigating subsurface electrical structures. In recent years, 3D inversion of AEM data is being developed rapidly, but it still faces challenges such as low resolution and computational efficiency. To solve these problems, we propose a multiscale shearlet-...

Satellite magnetic data contain significant information about the Earth’s interior electrical structure. However, the altitudes of satellites vary over time and latitude. Theoretically, the signals from the external magnetosphere and ionosphere, along with the induced magnetic field from the Earth, exhibit considerable variation at different altitu...

Previous works have demonstrated that inverting MT data jointly with gravity data can synergize the high lateral resolution of gravity and the vertical resolution of MT. However, the existing joint stabilizers usually work for structured grids instead of unstructured ones that are more powerful for characterizing complex geology. Here, we utilize L...

Slow forward modeling is the main factor that restricts the practical use of three-dimensional (3D) inversion and interpretation of airborne electromagnetic (AEM) data. To improve the modeling efficiency in 3D AEM, we propose a new multiscale finite-element (MsFE) method based on unstructured hexahedral meshes. Compared with the traditional 3D AEM...

At present, the mainstream technology for leachate detection in landfills is electrical resistivity tomography (ERT), known for its efficiency and non-destructive nature. However, the conventional ERT data interpretation primarily uses inversion based on structured grids, which cannot accurately simulate the complex and thin impermeable layers of l...

Transient electromagnetic method (TEM) surveys in engineering geophysics research can be used to detect geological anomalies caused by water. In this study, a hybrid-dimensional TEM data inversion method was developed to produce high-resolution results for detecting water hazards in coal mines, solving the problem of misestimating water hazard anom...

In mineral, environmental, and engineering explorations, we frequently encounter geological bodies with varied sizes, depths, and conductivity contrasts with surround rocks and try to interpret them with single survey data. The conventional three-dimensional (3-D) inversions significantly rely on the size of the grids, which should be smaller than...

Many mineral deposits demonstrate low-resistivity characteristics. This property makes the electromagnetic (EM) method a very useful tool for mineral exploration. In the past decades, the application of EM exploration technologies has been reviewed in many case studies. However, most reviews focused on EM exploration methods, the development of equ...

The conventional geo-electromagnetic data inversions are mostly based on the gradient optimization methods. However, this type of methods can only provide single “optimal” inverse model under specific prior conditions, which cannot effectively evaluate the reliability and uncertainty of the inversion results. The widely used uncertainty quantificat...

We propose a novel method for 3-D magnetotelluric (MT) forward modelling based on hybrid meshless and finite-element (FE) methods. This method divides the earth model into a central computational region and an expansion one. For the central region, we adopt scatter points to discretize the model, which can flexibly and accurately characterize the c...

The airborne electromagnetic (AEM) method can be used to effectively explore underground conductivity structures at high resolution. Conventional three-dimensional (3D) AEM inversions are mainly based on gradient-type deterministic methods; however, their results cannot be evaluated without bias because they only provide an updated model from an in...

Airborne electromagnetic (AEM) surveys usually covers a large area and create a large amount of data. This has limited the application of three-dimensional (3D) AEM inversions. To make 3D AEM data inversion at a large scale possible, the local mesh method has been proposed to avoid solving large matrix equations in 3D AEM modeling. However, the loc...

The choice of data misfit measure has a great impact on the convergence of electromagnetic (EM) inversion. The conventional measure based on the $l_{2}$ -norm tends to excessively amplify the weights of a larger misfit, inadvertently neglecting data with a smaller misfit during the inversion process, thereby diminishing the resolution to a certai...

A time-domain finite-element method based on an arbitrary quadrilateral mesh is pro-posed to simulate two dimensional seismoelectric and electroseismic waves in SHTEmode. By decoupling the electrokinetic coupling equation, we can solve seismic wavesand electromagnetic waves independently. For the simulation of seismic wavefield, weutilize a more co...

Graphite is considered to be one of Europe’s most critical minerals. It is necessary for the transition from hydrocarbon fuel to electricity due to its use in batteries that power electronic devices and electric transport. In the past, high-quality exposed graphite was found in Norway without today’s advanced geophysical and geological methods. Nor...

The finite-element (FE) method for three-dimensional (3D) airborne electromagnetic (AEM) modeling can flexibly simulate complex geological structures at high accuracy. However, it has low efficiency and high computational requirements. To solve these problems, one needs to generate meshes more reasonably. In view of this, we develop an adaptive oct...

We propose a novel smoothing regularization scheme for three-dimensional (3D) magnetotelluric (MT) inversion based on unstructured tetrahedral discretization. Different from conventional methods that explicitly add smoothing constraints to model parameters, we choose to do the gradient filtering to smooth the model updates in an implicit way. By tr...

The flight altitude has a large effect on the airborne electromagnetic (AEM) responses. Due to the dynamic environment of the aircraft, the recorded sensor altitudes may contain errors. Research demonstrates that the AEM responses caused by a several meters altitude errors can be larger than caused by some anomalous body. Ignoring these errors will...

In a sedimentary environment, the conventional one-dimensional (1D) inversion based on the horizontal layered model has difficulty restoring the resistivity distribution of the inclined strata when a coal seam has some dip angle or a small interval between layers. In such cases, the inversion resistivity exhibits horizontal discontinuities, which c...

The surface-to-borehole transient electromagnetic (SBTEM) method can provide images at higher resolution for deep earth because its receivers are close to targets. However, as usually the boreholes distribute sparsely, the limited EM data can result in an “equivalent trap” in SBTEM inversions, i.e., the data are well-fitted, but the model is not pr...

Airborne electromagnetic (AEM) exploration produces large amounts of data due to its high sampling rate, so that the three-dimensional (3D) inversions take extremely big computation and time consumption. We present a fast 3D inversion framework for large-scale AEM explorations using a preconditioned stochastic gradient descent combined with Gauss-N...

For the mineral exploration in complex terrain areas, the semi-airborne transient electromagnetic (SATEM) technology is one of the most powerful methods due to its high efficiency and low cost. However, since the mainstream SATEM systems only observe the component dBz/dt and the data are usually processed by simple interpretation or one-dimensional...

The traditional three-dimensional (3D) magnetotelluric (MT) forward modeling using Krylov subspace algorithms has the problem of low modeling efficiency. To improve the computational efficiency of 3D MT forward modeling, we present a novel geometric multigrid algorithm for the finite element method. We use the vector finite element to discretize Ma...

The conventional magnetotelluric (MT) data inversion methods, such as the nonlinear conjugate gradient method, quasi-Newton method, and Gauss-Newton method and so on, can converge robustly, but their results are easily affected by the initial model and regularization term. Although supervised learning can break through the resolution limitation by...

In a heterogeneous medium (usually called a rough medium) with fractured formations, the propagation of an electromagnetic (EM) field is a type of subdiffusion. Current mainstream geophysical EM data processing methods cannot be applied to data acquired on heterogeneous earth, as they are not governed by the classic diffusion theory. To evaluate th...

The seismoelectric effect is a coupling phenomenon between the seismic wave field and electromagnetic field caused by the electric double layer in a fluid-saturated porous medium. As seismoelectric signals are sensitive to porous medium properties, such as the water saturation, salinity, porosity, and permeability, they have good potential for imag...

Gravity inversion is a typical geophysical inversion method that obtains the underground density distribution by analyzing the gravity anomaly. Normally, it can be divided into geophysics-based and deep learning based inversion. The 3D geophysics-based inversion is a time- and memory-consuming method, so 3D inversion is not routinely implemented in...

We propose a new three‐dimensional anisotropic inversion scheme for magnetotelluric (MT) data. In this method, the earth is discretized into unstructured tetrahedral grids that can fit complex structures well, such as the earth topography and coastline. We use a 3 × 3 tensor to describe the anisotropic conductivity in the governing equation for MT...

Two efficient implementations of 3D and 2.5D modeling and inversion are presented to be applicable to large-scale transient electromagnetic (TEM) method explorations. The key novel features are (1) forward response and Jacobian calculations are implemented using the octree-based finite-element method, (2) a mirror approach is used to build a 2.5D i...

The manuscript was processed without taking into account the authors’ modifications based on the last comments of reviewers, mainly in-text citations. These have now been added to the original article.

Three-dimensional (3D) airborne electromagnetic (AEM) inversions have been restricted by the modeling efficiency resulted from the complex geology in exploration areas and massive amount of data collected by AEM systems. In order to improve the modeling efficiency, we develop an algorithm that combines the hexahedral vector finite-element (FE) with...

Airborne systems collecting transient electromagnetic data are able to gather large amounts of data over large areas in a very short time. These data are most often interpreted through 1D inversions, due to the availability of robust, fast and efficient codes. However, in areas where the subsurface contains complex structures or large conductivity...

Based on the spatial structure correlation in different geophysical parameters, we propose a new three-dimensional (3D) joint inversion method for frequency-domain airborne electromagnetic (AEM) and airborne magnetic (AirMag) data by incorporating a local Pearson correlation constraint (LPCC). For each iteration, the entire model is separated into...

Spontaneous coal combustion is a serious hazard that affects mining safety. Since the coal seams are thin and their resistivity dramatically changes during spontaneous combustion, locating the burned cavities or caving zones using electromagnetic (EM) methods is challenging. The conventional transient electromagnetic (TEM) method with a loop transm...

We present a wavelet finite-element method (WFEM) based on B-spline wavelets on the interval (BSWI) for three-dimensional (3D) frequency-domain airborne EM modeling using a secondary coupled-potential formulation. The BSWI, which is constructed on the interval (0, 1) by joining piecewise B-spline polynomials between nodes together, has proved to ha...

The spectral-element (SE) method, which is based on the Galerkin technique, has been gradually implemented in geophysical electromagnetic (EM) three-dimensional (3D) simulation. The accuracy and efficiency of this approach, implemented for both deformed hexahedral and regular meshes, has been verified for airborne EM forward modeling. One advantage...

Airborne electromagnetic (AEM) methods have been more and more widely used in mineral exploration, environmental and engineering studies, and ground water investigation. However, compared with ground-based electromagnetic (EM) methods, such as magnetotelluric or controlled-source EM, AEM methods generally produce large amount of data, which leads t...

Inversion of large-scale time-domain transient electromagnetic (TEM) surveys is computationally expensive and time-consuming. The calculation of partial derivatives for the Jacobian matrix is by far the most computationally intensive task, as this requires calculation of a significant number of forward responses. We propose to accelerate the invers...

The conventional, L2-norm-based, regularization term in electromagnetic (EM) inversions implements smooth constraints on model complexity in the space domain, which can smoothen the boundaries of complex underground structures. To improve the resolution of 3-D frequency-domain airborne EM (AEM) inversions, we propose a new algorithm for sparse-regu...

During several decades, much research has been done to develop 3D electromagnetic inversion algorithms. Due to the computational complexity and the memory requirements for 3D time domain electromagnetic (TEM) inversion algorithms, many real world surveys are inverted with in 1D. To speed up calculations and manage memory for 3D inversions of TEM da...

The conventional 3D magnetotelluric (MT) forward modeling and inversions generally assume an isotropic earth model. However, wrong results can be obtained when using an isotropic model to interpret the data influenced by the anisotropy. To effectively model and recover the earth structures including anisotropy, we develop a 3D MT inversion framewor...

In this study, we propose a three-dimensional (3D) forward modeling algorithm of surface-to-borehole transient electromagnetic (SBTEM) fields based on an unstructured vector finite-element method to analyze the characteristics of SBTEM responses for complex geoelectrical models. To solve the double-curl diffusion equation for the electric field, we...

Rocks and ores in nature usually appear macro-anisotropic, especially in sedimentary areas with strong layering. This anisotropy will lead to false interpretation of electromagnetic (EM) data when inverted under the assumption of an isotropic earth. However, the time-domain (TD) airborne EM (AEM) inversion for an anisotropic model has not attracted...

Inversion of large-scale time-domain electromagnetic surveys are computationally expensive and time consuming. Deterministic or probabilistic inversion schemes usually require calculations of forward responses, and often thousands to millions of forward responses are computed. We propose a machine learning based forward modelling approach as a comp...

Soil organic matter (SOM) is rich in black soil area. It has a significant effect on soil health and luxuriant vegetation. The agricultural production activities can thus be guided by measurements of SOM at different periods. Most of previous work estimated SOM using reflectance spectra measurements on dried soil samples, to remove the effect of so...

We propose a new 3D inversion scheme to invert the near- and transition-zone data of CSAMT with topography accurately. In this new method, the earth was discretized into unstructured tetrahedra to fit the ragged topography and the vector finite-element method was adopted to obtain precise responses and good sensitivity. To simulate the attitude and...

In this paper, we propose a new method for two-dimensional (2-D) magnetotelluric (MT) inversion based on the curvelet transform. Unlike the conventional inversion methods that apply constraints on the model in the space-domain, the method presented in this paper is based on the sparse constraint by the curvelet transform, and we directly invert the...

The spectral element method (SEM) based on high-order complete orthogonal polynomials is an accurate and efficient numerical method for electromagnetic modelling due to its spectral accuracy and exponential convergence. The SEM combines the flexibility of the finite-element method and the high accuracy of the spectral method. In this paper, we intr...

S U M M A R Y We introduce a novel block rational Krylov method to accelerate 3-D time-domain marine controlled-source electromagnetic modelling with multiple sources. This method approximates the time-varying electric solutions explicitly in terms of matrix exponential functions. A main attraction is that no time stepping is required, while most o...

The unstructured finite-element method has been widely used in 3D time-domain electromagnetic (EM) modeling due to its flexibility for modeling rugged topography and complex underground structures. However, how to generate high-quality grids becomes the key to high-accuracy EM responses. We have developed a weighted goal-oriented adaptive finite-el...

S U M M A R Y The transient electromagnetic (TEM) data acquired in mountainous area are seriously affected by topography, implying that consideration of topographic effect in the interpretation is in urgent need. To deal with this problem, we propose a new method to invert TEM data by simulating the topography. The unstructured tetrahedral grid wit...

Since Airborne Electromagnetic (AEM) survey produces massive data, an effective imaging and inversion tool is very important. In this work, we take a layered earth model as an example to derive the one-dimensional (1D) time-domain AEM inversion under generalized model constraints. Starting from the objective functional for the regularized inversion...

We investigate an algorithm for 3D time-domain AEM inversion with the finite-volume and direct Gauss-Newton methods. We separate a spatially varying secondary field from the 1D background in time-domain, and constrain the calculation to be within the small volume of influence of airborne EM secondary source, resulting in more compact discretization...

Spectral-element (SE) method is a kind of higher-order finite-element method based on weighted residual technique; however, the basis functions for SE are polynomial, like Gauss-Lobatto-Legendre (GLL) or Gauss-Lobatto-Chebyshev (GLC) polynomials. Because of its high modeling accuracy and flexibility, it has been successfully used in computational e...

Mainstream numerical methods for 3D time-domain airborne electromagnetic (AEM) modeling, such as the finite-difference (FDTD) or finite-element (FETD) methods, are quite mature. However, these methods have limitations in terms of their ability to handle complex geologic structures and their dependence on quality meshing of the earth model. We have...

Traditional 3D Magnetotelluric (MT) forward modeling and inversions are mostly based on structured meshes that have limited accuracy when modeling undulating surfaces and arbitrary structures. By contrast, unstructured-grid-based methods can model complex underground structures with high accuracy and overcome the defects of traditional methods, suc...

Traditional 3D Magnetotelluric (MT) forward modeling and inversions are mostly based on structured meshes that have limited accuracy when modeling undulating surfaces and arbitrary structures. By contrast, unstructured-grid-based methods can model complex underground structures with high accuracy and overcome the defects of traditional methods, suc...

Electrical anisotropy exists everywhere in nature that has become an important issue non-ignorable in geophysical exploration. Especially in areas of sedimentary rocks where strata in the earth result in variation of resistivity varying with the direction of current flow. In this paper, we review the research on electrical anisotropy in geo-electro...

To reduce the dependence of EM inversion on the choice of initial model and to obtain the global minimum, we apply transdimensional Bayesian inversion to time-domain airborne electromagnetic data. The transdimensional Bayesian inversion uses the Monte Carlo method to search the model space and yields models that simultaneously satisfy the acceptanc...

Traditional 3D MT data interpretations are based on an isotropic model that is sometimes inappropriate, because it has been well established that electrical anisotropy is widely present in the deep earth. The MT anisotropic modelling is generally worked on structured meshes that has a limited accuracy but cannot model complex geology. We present a...

We investigate an algorithm for 3D time-domain airborne electromagnetic (AEM) inversion based on the finite-volume (FV) method and direct Gauss-Newton optimization, where we obtain high efficiency by constraining the modeling volume to the AEM volume of influence (VOI) of a 3D source within the earth, rather than using the larger VOI of the AEM sys...

A dual-ship-towed marine electromagnetic (EM) system is a new marine exploration technology recently being developed in China. Compared with traditional marine EM systems, the new system tows the transmitters and receivers using two ships, rendering it unnecessary to position EM receivers at the seafloor in advance. This makes the system more flexi...

Marine controlled-source electromagnetic (MCSEM) method is an important predrill reservoir appraisal method to reduce exploration risk in detecting sub-seafloor hydrocarbon reservoirs. Most 3D forward modelings for MCSEM are based on conventional numerical methods like finite-difference and finite-element method. In this paper, we introduce spectra...

In an integral equation (IE) method, the storage of Green's coefficient matrix and solution of linear equation system are always challenging for its development and application. Quasi-linear (QL) approximation method assumes that a linear relationship exists between the background and abnormal field. It can deal with nonlinear problems effectively....

Airborne electromagnetic (AEM) forward modeling has been extensively developed in past years. However, not much attention has been paid to the adaptive numerical algorithms for time-domain electromagnetic modeling. We have created an adaptive method that can generate an effective mesh for time-domain 3D AEM full-wave modeling using an unstructured...

The airborne electromagnetic (AEM) method has a high sampling rate and survey flexibility. However, traditional numerical modeling approaches must use high-resolution physical grids to guarantee modeling accuracy, especially for complex geological structures such as anisotropic earth. This can lead to huge computational costs. To solve this problem...