• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.314-321
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• 2007

Recently, multi-dimensional joint inversion of geophysical data based on fundamentally different physical properties is being actively studied. Joint inversion can provide a way to obtaining much more accurate image of the subsurface structure. Through the joint inversion, furthermore, it is possible to directly estimate non-geophysical material properties from geophysical measurements. In this study, we developed a new algorithm for jointly inverting dc resistivity and seismic traveltime data based on the multiple constraints: (1) structural similarity based on cross-gradient, (2) correlation between two different material properties, and (3) a priori information on the material property distribution. Through the numerical experiments of surface dc resistivity and seismic refraction surveys, the performance of the proposed algorithm was demonstrated and the effects of different regularizations were analyzed. In particular, we showed that the hidden layer problem in the seismic refraction method due to an inter-bedded low velocity layer can be solved by the joint inversion when appropriate constraints are applied.

• Economic and Environmental Geology
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• v.27 no.5
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• pp.479-489
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• 1994

In this paper, the iterative least-squares inversion method is used to determine shapes and density contrasts of 2-D structures from the gravity data. The 2-D structures are represented by their cross-sections of N-sided polygons with density contrasts which are constant or varying with depth. Gravity data are calculated by theoretical formulas for the above structure models. The data are considered as observed ones and used for inversions. The inversions are performed by the following processes: I) polygon's vertices and density contrast are initially assumed, 2) gravity are calculated for the assumed model and error between the true (observed) and calculated gravity are determined, 3) new vertices and density contrast are determined from the error by using the damped least-squares inversion method, and 4) final model is determined when the error is very small. Results of this study show that the shape and density contrast of each model are accurately determined when the density contrast is constant or vertical density gradient is known. In case where the density gradient is unknown, the inversion gives incorrect results. But the shape and density gradient of the model are determined when the surface density contrast is known.

• Geophysics and Geophysical Exploration
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• v.1 no.1
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• pp.71-78
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• 1998

Inversion schemes of 2-D MT survey data generally take enormous computational time and computer memory. In addition, careful attention must be paid in handling MT data, especially in cases of TM mode, inversion results can be seriously distorted because of static effect caused by current channeling across inhomogeneous surface boundaries. There-fore inversion algorithm using the GRRI scheme for TM mode MT data was implemented. This scheme is based on a perturbation analysis with a locally 2-D analysis and local inversions were sequently performed over each divided section without additional forward modelings. The algorithm was applied to several synthetic data for the purpose of verification of its efficiency and applicability. With less computer resources than conventional schemes, it could handle static effect directly by including current channeling across inhomogeneous boundaries. Thus it is expected to be used for an useful tool such as a real-time inversion scheme in the field.

• Geophysics and Geophysical Exploration
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• v.4 no.2
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• pp.25-33
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• 2001

Loop-loop electromagnetic (EM) survey in frequency domain has been carried out in order to provide basic solution to geotechnical applications. Source and receiver configuration may be horizontal co-planar (HCP) and/or vertical co-planar (VCP). Three quadrature components of mutual impedance ratio for each configuration are used to construct the subsurface image. For the purpose of obtaining the model response and validating the reasonable performance of the inversion, we obtained each responses of two-layered and three-layered earth models and two-dimensional (2-D) isolated anomalous body. The response of 2-D isolated anomalous body has been calculated using extended Born approximation for the solution of 2.5-D integral equation describing EM scattering problem. As a result of the least-squares inversion with variable Lagrangian multiplier, we could construct more resolvable image from HCP data than VCP data. Furthermore, joint inversion of HCP and VCP data made better stability and resolution of the inversion. Resistivity values, however, did not exactly match the true ones. Loop-loop EM field data was obtained with EM34-3XL system manufactured by Geonics Ltd. (Canada). Electrical resistivity survey was conducted on the same line for the comparison in advance. Since the constructed image from loop-loop EM data by 2-D inversion algorithm showed almost similar resistivity distribution to that from electrical resistivity one, we expect the developed 2.5-D loop-loop EM inversion program can be applied for the reconnaissance site survey.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.308-313
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• 2015

This paper describes a technique for complete identification of a two-dimensional scattering object and multiple objects immersed in air using microwaves where the scatterers are assumed to be a homogenous dielectric medium. The employed technique consists of initially retrieving the shape and position of the scattering object using a linear sampling method and then determining the electric permittivity and conductivity of the scatterer using adjoint sensitivity analysis. Incident waves are assumed to be TM (Transverse Magnetic) plane waves. This inversion algorithm results in high computational speed and efficiency, and it can be generalized for any scatterer structure. Also, this method is robust with respect to noise. The numerical results clearly show that this hybrid approach provides accurate reconstructions of various objects.

• Geophysics and Geophysical Exploration
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• v.27 no.2
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• pp.129-143
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• 2024

In magnetotelluric (MT) surveys, small inhomogeneities near the surface cause a static shift in which apparent resistivities shift regardless of frequency. As the static shift in MT data leads to errors in subsurface structure interpretation, many studies have been conducted over the past few decades to mitigate or remove the distortions it caused. The most representative method involves removing static shifts from the data before inversion. Conversely, static shifts can be corrected during inversion or included in the inversion process. In addition, other geophysical data can be used to remove static shifts. However, the correction methods are limited to one-dimensional (1D) static responses, and limitations remain in two- or three-dimensional (2D or 3D) interpretation of distorted MT data owing to static shifts. This study provides a foundation for future studies on static shift by analyzing several previously published methods.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.424-427
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• 2017

This study investigated the effect of strain on hole mobility and hole effective mass in a p-channel rectangular nanowire with two-dimensional confinement. We obtained the valence energy band structure using the six-band k.p method and calculated the mobility and effective mass of the hole in the [100] direction taking the strain effect into account in the inversion region. The hole mobility of strained silicon was calculated using Kubo-Greenwood formalism. As a result, it showed good performance compared to relaxed silicon, but its magnitude was insignificant.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.11
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• pp.1-7
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• 2008

In this work, a two dimensional, self-consistent Poisson-$Schr{\ddot{o}}dinger$ solver has been implemented to study C-V characteristics in nanometer scale MuGFETs with considering quantum effects. The quantum-mechanical effects on gate-channel capacitance for different device dimension and gate configurations of nanometer scale MuGFETs have been analyzed. It has been found that 4he gate-channel capacitance per unit gate area is increased as the device dimension decreases. For different gate configurations, the gate-channel capacitance is decreased with increase of effective gate number. Those resu1ts have been explained by the distribution profile of electron concentration in the silicon surface and inversion capacitance. The length of inversion-layer centroid has been calculated from inversion capacitance with device dimension and gate configurations.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.362-367
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• 2003

It is shown that the effect of variable parameters on flame structures and NOx emissions in the laminar partially premixed methane-air flames with a co-axial Bunsen burner. Objectives of this paper is to understand the effects of flow variables on NOx emissions and the flame structure with OH chemiluminescence, including reconstructed image by abel inversion processing at each conditions. A fuel flowrate of 200 [cc/min] was fixed and the amount of air was varied from 400 to 1200 [cc/min]. The experimental variables were equivalence ratio(${\Phi}$ fuel split percentage(${\sigma}$ and inner tube recess(x/D). Flow conditions were ranged from $1.36{\sim}4.76$(equivalence ratio), $50{\sim}100$(fuel split percentage) and $0{\sim}20$(inner tube recess). NOx analyzer and ICCD camera with a OH filter were used as a main experimental apparatus. In addition, Abel inversion, which is a kind of tomography and valuable to estimate a two-dimensional structure of co-axial flames from cubical information, was employed for combustion diagnostics. Results from this study indicate that the main effects depend on equivalence ratio and next sigma, x/D for NOx production and OH formation. Throughout Abel inversion, we could affirm the maximum position and the tendency of OH radical intensity by variants at five axial heights above the burner exit.

• Geophysics and Geophysical Exploration
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• v.1 no.1
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• pp.19-24
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• 1998

This paper deals with tomographic travel time inversion of three dimensional seismic refraction survey conducted over a dipping interface. The slowness, and thus velocity as its reciprocal, distribution on the subsurface interface is to be determined applying an ART with under-relaxtion parameter. The models chosen are realistic, i.e., most likely to be met in engineering seismics, and the interface includes anomalous zones. It is found that, generally speaking, the inversion could be misleading or meaningless without the correction of the dip of the interface. This is rather surprising when we recall that usual assumption for the interpretation of refraction seismics data is the horizontal attitude of structures within the limit of $15^{\circ}$ dip or so. To make the present method tenable for a new means of routine seismics, some practical ways of identifying head wave arrivals are to be devised.