• Geophysics and Geophysical Exploration
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• v.22 no.3
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• pp.160-167
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• 2019

Resistivity inversion result may be distorted if the seepage line fluctuation within central core with the change of reservoir water level as well as the conductivity of the reservoir water is not taken into consideration because the reservoir dike is composed of three-dimensional (3D) resistivity structure. Consequently, to accurately analyze the resistivity changes inside the reservoir dike according to the change of reservoir water level, 3D electrical resistivity modeling for the 2D survey line considering topography and physical properties of dam components was carried out. In addition, 2D inversion was performed with the simulated 2D resistivity data for a given 3D model in order to compare it with the inversion result of real field data. For 283 reservoirs in Korea, 2D inversion results for the simulated 2D data and field 2D resistivity data were compared. Finally, the reservoirs with an inversion ratio of 50% or less were selected as reservoirs that require further precise investigation.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.33-42
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• 2017

Recently, the grounded electrical-source airborne transient electromagnetic (GREATEM) system with high power source was introduced to achieve deeper investigation depth and to overcome high noise level. Although the GREATEM is a transient electromagnetic system using a long grounded wire as the transmitter, GREATEM data have been interpreted with 1D earth models because 2D or 3D modeling and inversion of vast airborne data are complicated and expensive to calculate. Generally, 1D inversion is subsequently applied to every survey point and combining 1D images together forms the stitched conductivity-depth image. However, the stitched models often result in abrupt variations in neighboring models. To overcome this problem, laterally constrained inversion (LCI) has been developed in inversion of ATEM data, which can yield layered sections with lateral smooth transitions. In this study, we analysed the GREATEM data through 1D numerical modeling for a curved grounded wire source. Furthermore, we developed a laterally constrained inversion scheme for continuous GREATEM data based on a layered earth model. All 1D data sets and models are inverted as one system, producing layered sections with lateral smooth transitions. Applying the developed LCI technique to the GREATEM data, it was confirmed that the laterally constrained inversion can provide laterally smooth model sections that reflect the layering of the survey area effectively.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.167-172
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• 2007

The frequency-domain small-loop electromagnetic (EM) instruments are increasingly used for shallow environmental and geotechnical surveys because of their portability and speed. However, it is well known that the data quality is generally so poor that quantitative interpretation of the data is not justified in many cases. We present an inversion method that allows the correction for the calibration errors and also constructs multidimensional resistivity models. The key point in this method is that the data are collected at least at two different heights. The forward modeling used in the inversion is based on an efficient 3-D finite-difference method, and its solution was checked against 2-D finite-element solution. The synthetic and real data examples demonstrate that the joint inversion recovers reliable resistivity models from multi-frequency data severely contaminated by the calibration errors.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.322-324
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• 2003

Leaf C:N ratio is a new factor in the field of biochemical inversion with hyperspectral data. Effects of common-used spectral transformations including log(R), log(1/R), 1/R, etc. from 400nm to 2490nm on its inversion are compared. Results show that their effects on statistical modeling are not apparent. Continuum removal is used on original reflectance in the range of 2030nm to 2220nm, in which exists an apparent absorption peak due to cellulose, lignin, protein, etc. The effect is distinctive and tends to improve the precision of C:N ratio inversion. Further, it is a robust and physically based transformation.

• Geophysics and Geophysical Exploration
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• v.16 no.1
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• pp.27-35
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• 2013

In this study, we developed the trial product on 3D magnetic inversion tentatively named 'KMag3D'. Also, we briefly introduced its own function and graphic user interface on which especially focused through the development in the form of user manual. KMag3D is consisted of two fundamental frame for the 3D magnetic inversion. First, algebraic reconstruction technique was selected as a 3D inversion algorithm instead of least square method conventionally used in various magnetic inversion. By comparison, it was turned out that algebraic reconstruction algorithm was more effective and economic than that of least squares in aspect of both computation time and memory. Second, for the effective determination of the 3D initial and a-priori information model required in the execution of our algorithm, we proposed the practical technique based on the assemblage of 2D forward modeling and inversion results for individual user-selected 2D profiles. And in succession, initial and a-priori information model were constructed by appropriate interpolation along the strke direction. From this, we concluded that our technique is both suitable and very practical for the application of 3D magentic inversion problem.

• Geophysics and Geophysical Exploration
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• v.2 no.1
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• pp.43-53
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• 1999

Numerical modeling and inversion for electromagnetic exploration methods are essential to understand behaviour of electromagnetic fields in complex subsurface. In this study, a finite element method was adopted as a numerical scheme for the 2.5-dimensional forward problem. And a finite element equation considering linear conductivity variation was proposed, when 2.5-dimensional differential equation to couple eletric and magnetic field was implemented. Model parameters were investigated for near-field with large source effects and far-field with responses dominantly by homogeneous half-space. Numerical responses by this study were compared with analytic solutions in homogeneous half-space. Blocky inversion model was modified to be applied to the forward calculation in this study and it was also adopted in the inversion algorithm. Resolution for isolated bodies were investigated to confirm possibility and limitation of inversion for electromagnetic exploration data.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.185-190
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• 2007

In this study, we developed the 2.5D EM modeling and inversion algorithm for cross-hole source and receiver geometry. Considering the cross-hole environment, we use a VMD (vertical magnetic dipole) as a source and vertical magnetic fields as a measuring data. Developed inversion algorithm is tested for the isolated block model which has a conductive and a resistivity anomaly respectively. For the conductive anomaly, its size and resistivity are inverted well on the inversion results, while for the resistive anomaly, the location of anomalous block is shown on the inverted section, but its values are far from the exact value. Furthermore, artificial conductive anomalies are shown around the resistive anomalous zone. If we consider the inversion artifact shown in the test inversion of restive block, it is almost impossible to image the resistive zone. However, the main target of EM tomography in the engineering problem is conductive target such as fault zone, and contaminated zone etc., EM tomography algorithm can be used for detecting the anomalous zone.

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.191-201
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• 1999

The interpretation of resistivity data has, so far, mainly been made under the assumption that the earth is of relatively simple structure and then using one or two-dimensional inversion scheme. Since real earth structure and topography are fully three-dimensional and very complicated In nature, however, such assumptions often lead to misinterpretation of the earth structures. In such situations, three-dimensional inversion is probably the only way to get correct image of the earth. In this study, we have developed a three-dimensional inversion code using the finite element solution for the forward problem. The forward modeling algorithm simulates the real field situation with irregular topography. The inverse problem is solved iteratively using the least-squares method with smoothness constraint. Our inversion scheme employs ACB (Active Constraint Balancing) to enhance the resolving power of the inversion. Including Irregular surface topography in the inversion, we can accurately define the earth structures without artifact in the numerical tests. We could get reasonable image of earth structure by Inverting the real field data sets taken over highway bridge construction site.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.4
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• pp.34-41
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• 1999

Unlike the traditional radar system, Synthetic Aperture Radar(SAR) system is capable of imaging a target scene to ceertain degree of cross-range resolution. And this resolution is mainly depends on the size of aperture synthesized. Thus, a good system model and inversion scheme should be developed to actually give effect of synthesizing aperture size, which in turn gives better cross range resolution of reconstructed target scene. Among several inversion schemes for SAR imaging, we used an inversion scheme called wavefront reconstruction which has no approximation in wave propagation analysis, and tried to verify whether the collected data with synthesized aperture actually give the same support as that with physical aperture in the same size. To do this, we performed a signal subspace comparison of two imaging models with physical and synthesized arrays, respectively. Theoretical comparisons and numerical analysis using Gram-Schmidt procedures have been performed. The results showed that the synthesized array data fully span the physical array data with the same system geometry. This result strongly supports the previously proposed inversion scheme valuable in high resolution radar imaging.

• The Journal of the Acoustical Society of Korea
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• v.18 no.8
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• pp.32-41
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• 1999

In this paper, an inversion method using chirp signals and two near field receivers is proposed. Inversion problems can be formulated into the probabilistic models composed of signals, a forward model and noise. Forward model to simulate chirp signals is chosen to be the source-wavelet-convolution planewave modeling method. The solution of the inversion problem is defined by a posteriori pdf. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the ranges for a priori uniform distribution is based. The genetic algorithm can be applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L₂norm of the difference between measured and modeled signals. The observed signals can be separated into a set of two signals reflected from the upper and lower boundaries of a sediment. The separation of signals and successive applications of the genetic algorithm optimization process reduce the search space, therefore improving the inversion results. Not only the marginal pdf but also the statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm. The examples applied here show that, for synthetic data with noise, it is possible to carry out an inversion for sedimentary layers using the proposed inversion method.