• 한국지구물리탐사학회:학술대회논문집
• /
• 한국지구물리탐사학회 2007년도 공동학술대회 논문집
• /
• pp.54-57
• /
• 2007

Recently, multidimensional joint inversion of geophysical data based on fundamentally different physical properties has been actively studied. Joint inversion can provide a way to much more accurately image the subsurface structure. Through the joint inversion, furthermore, it is possible to directly estimate non-geophysical material properties from geophysical measurements. In this study, I derive the objective functions and normal equations of three different joint inversion approaches: one approach based on the structural similarity using cross-gradient, and the other two using the a priori information on the model parameters and the correlation between material properties. Since all the equations derived in this study are based on the same inversion method (smoothness constrained least-squares), it is possible to mix the joint inversion methods so as to produce a new joint inversion algorithm.

• 지구물리와물리탐사
• /
• 제25권4호
• /
• pp.252-265
• /
• 2022

지하 매질의 물성 정보는 지층 구조의 정확한 영상화를 위해 필요하며, 예측된 매질 물성 자체도 지하 매질 특성에 대한 중요한 정보를 제공해줄 수 있기 때문에 다양한 종류의 지층 물성 도출 알고리듬들이 개발되고 적용되어왔다. 그 중 마르코프 연쇄 몬테 카를로를 이용한 확률론적인 접근 방법은 기존의 결정론적인 접근 방법과는 달리 지역 최소값 문제를 완화시킬 수 있으며 역산 결과의 불확실성을 정량화할 수 있다는 부분에서 장점을 가진다. 따라서 마르코프 연쇄 몬테 카를로를 이용한 지층 물성 역산 알고리듬이 다양한 지구 물리 자료의 역산에 적용되어 왔으나 그 사례는 결정론적 접근 방법에 비해 매우 적다. 본 논문에서는 여러 형태의 마르코프 연쇄 몬테 카를로 역산 알고리듬 중 가역 도약을 적용한 가역 도약 마르코프 연쇄 몬테 카를로 역산을 탄성파 자료 역산에 적용한 다양한 사례들을 소개하고 각각의 특성을 설명한다. 또한 가역 도역 마르코프 연쇄 몬테 카를로 역산의 장단점에 대해 분석하고 향후 해당 알고리듬의 연구 방향 및 국내의 활용성에 대해 논의한다.

• 지구물리와물리탐사
• /
• 제8권2호
• /
• pp.163-169
• /
• 2005

속도중합을 역산을 이용하면 탄성파 자료처리에서 있어서 다양한 처리가 가능하므로, 이 분야는 최근에 들어 매우 유용한 영역으로 주목을 받고 있다. 이러한 다양한 처리에 속도중합 역산을 응용하기 위해서는 사용하는 역산이 잡음에 강하면서도 고해상도의 속도중합 결과를 얻을 수 있어야 한다. 이러한 성질을 갖는 역산 방법들 중에서 가장 성공적인 방법 중의 하나라고 볼 수 있는 반복적 가중의 최소자승법(Iteratively Reweighted Least-Squares: IRLS)의 이론적 배경과 구현 방법을 소개하고, 기존 기술 특성과 한계성을 살펴보았다.

• 한국지구물리탐사학회:학술대회논문집
• /
• 한국지구물리탐사학회 2006년도 공동학술대회 논문집
• /
• pp.131-135
• /
• 2006

본 논문에서는 가우스 뉴튼법을 이용한 중합전 탄성파 자료의 파형역산에 관한 연구를 수행하였다. 탄성파 파형역산에 가우스 뉴튼법을 적용하는 방법은 80년대에 제시되었으나 최근 들어서야 활발히 연구가 진행되고 있는데 이는 연산 능력과 기억용량의 한계에 기인한 것이다. 이를 극복하기 위해 본 연구에서는, 파동 전파 수치모의와 역산과정에서 각각 다른 크기의 격자간격을 사용하고, 필요한 시간영역의 파동전파 모사와 가상 진원의 근사를 통해 편미분 파형을 계산하였으며, 효과적으로 슈퍼컴퓨터를 활용하기 위해 병렬처리 기법을 사용하였다. 수치모의를 통해, 가우스 뉴튼법을 이용한 파형 역산의 수렴속도가 빠르고 정확한 것을 알 수 있었으며, 이를 통해 본 연구에서 제시한 방법의 실제 탄성파 자료를 이용한 역산에의 적용가능성을 확인하였다.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• 제3B권2호
• /
• pp.67-73
• /
• 2003

In this paper, the impedance of a piezoelectric transducer is calculated using the three-dimensional finite element method. The validity of numerical routine is confirmed experimentally. Using this numerical routine, the effects of material coefficients on piezoelectric actuators characteristics are analyzed. The material constants, which make significant effects, are selected and the relations between material constants are studied. Using these processes, three variables of material constants for a piezoelectric transducer are selected and the design sensitivity method is adopted as an inversion scheme. The validity of the inversion scheme for a piezoelectric transducer is confirmed by applying the proposed method to the sample piezoelectric transducer.

• 한국지구물리탐사학회:학술대회논문집
• /
• 한국지구물리탐사학회 2007년도 공동학술대회 논문집
• /
• pp.167-172
• /
• 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.

• 대한자원환경지질학회:학술대회논문집
• /
• 대한자원환경지질학회 2002년도 춘계 공동학술발표회
• /
• pp.167-169
• /
• 2002

The extended Born, or localized nonlinear approximation of integral equation (IE) solution has been applied to inverting single-hole electromagnetic (EM) data using a cylindrically symmetric model. The extended Born approximation is less accurate than a full solution but much superior to the simple Born approximation. When applied to the cylindrically symmetric model with a vertical magnetic dipole source, however, the accuracy of the extended Born approximation is greatly improved because the electric field is scalar and continuous everywhere. One of the most important steps in the inversion is the selection of a proper regularization parameter for stability. Occam's inversion (Constable et al., 1987) is an excellent method for obtaining a stable inverse solution. It is extremely slow when combined with a differential equation method because many forward simulations are needed but suitable for the extended Born solution because the Green's functions, the most time consuming part in IE methods, are repeatedly re-usable throughout the inversion. In addition, the If formulation also readily contains a sensitivity matrix, which can be revised at each iteration at little expense. The inversion algorithm developed in this study is quite stable and fast even if the optimum regularization parameter Is sought at each iteration step. Tn this paper we show inversion results using synthetic data obtained from a finite-element method and field data as well.

• 한국지구물리탐사학회:학술대회논문집
• /
• 한국지구물리탐사학회 2007년도 공동학술대회 논문집
• /
• pp.209-214
• /
• 2007

In Korean geology that crystalline rock is dominant, the properties of subsurface including the anisotropy are distributed complexly and changed abruptly. Because of such geological environments, cross-hole seismic traveltime tomography is widely used to obtain the high resolution image of the subsurface for the engineering purposes in the geotechnical sites. However, because the cross-hole tomography has a wide propagation angle coverage relatively, its data tend to include the seismic velocity anisotropy comparing with the surface seismic methods. It can cause the misinterpretation that the cross-hole seismic data including the anisotropic effects are analyzed and treated with the general processing techniques assuming the isotropy. Therefore, we need to consider the seismic anisotropy in cross-hole seismic traveltime tomography. The seismic anisotropic tomography algorithm, which is developed for evaluation of the velocity anisotropy, includes several inversion schemes in order to make the inversion process stable and robust. First of all, the set of the inversion parameters is limited to one slowness, two ratios of slowness and one direction of the anisotropy symmetric axis. The ranges of the inversion parameters are localized by the pseudo-beta transform to obtain the reasonable inversion results and the inversion constraints are controlled efficiently by ACB(Active Constraint Balancing) method. Especially, the inversion using the Fresnel volume is applied to the anisotropic tomography and it can make the anisotropic tomography more stable than ray tomography as it widens the propagation angle coverage.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2002년도 춘계 학술발표회 논문집
• /
• pp.20-27
• /
• 2002

Conventional Levenberg-Marquardt's nonlinear inversion method is simply modified by taking into account the second derivatives of the Hessian matrix so as to give robust inversion results. The weight of the second derivative terms is determined by the value of so-called λ in Levenberg-Marquardt's method. The new inversion method is applied to observed data from small-to-moderate earthquakes to simultaneously evaluate the modes parameters of the stochastic point-source model in and around the Korean Peninsula. Best estimates of the stochastic model parameters are obtained along with their statistics and compared with the previous results. Overall characteristics of the model parameters are found to be more of those of interplate than intraplate tectonic region.

• 제어로봇시스템학회논문지
• /
• 제7권7호
• /
• pp.574-581
• /
• 2001

In this paper we design and evaluate the longitudinal nonlinear N(aub)z-CSAS(Command and Stability Augmentation System) flight control law in \"DMI(Dynamic Model Inversion)-method\" and classical \"Gain Scheduling-method\", respectively, to meet the handling quality requirements associated with push-over pull-up maneuver. It is told that the flight control law designed in \"DM-method\" is adequate to the full flight regime without gain scheduling and is efficient to produce the time response shape desired to the handling quality requirements. On the contrary, the flight control law designed in \"Gain Scheduling-method\" is easy to be implemented in flight control computer and insensitive to variation of the actuator model characteristics.n of the actuator model characteristics.