• Economic and Environmental Geology
• /
• v.22 no.3
• /
• pp.267-276
• /
• 1989

This paper presents results of interpretaton of gravity data by iterative nonlinear inversion methods. The gravity data are obtained by a theoretical formula for two-dimensional 2-layer structure. Depths to the basement of the structure are determined from the gravity data by four interative inversion methods. The four inversion methods used here are the Gradient, Gauss-Newton, Newton-Raphson, and Full Newton methods. Inversions are performed by using different initial guesses of depth for the over-determined, even-determined, and under-determined cases. This study shows that the depth can be determined well by all of the methods and most efficiently by the Newton-Raphson method.

• Geophysics and Geophysical Exploration
• /
• v.17 no.2
• /
• pp.104-113
• /
• 2014

Electric resistivity monitoring was applied to evaluate the soft ground in reclaimed land in order to figure out the applicability of physical prospecting. For this, electrical resistivity monitoring data were acquired for total three months and analyzed those data with independent inversion, time-lapse inversion, and 4D inversion methods. The result was compared for various inversion methods so as to figure out what showed the soft soil most properly. Moreover, drilling and CPT(Cone Penetration Test) data were also used in order to find out if each of those inversion methods could distinguish either bed rock or the soft soil clearly. And according to the result, time-lapse inversion showed less inversion artifacts than independent inversion, so it could indicate the soft soil better. If data gained for a longer period than three months are used, 4D inversion has been found to be a more efficient analysis method than the time-lapse inversion method. Electrical resistivity monitoring on the soft soil has been found to be a useful method that can analyze the spatio-temporal electric state of the ground serially.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.17 no.3
• /
• pp.425-437
• /
• 2017

For efficient hardware (HW) implementation of elliptic curve cryptography (ECC), various sub-modules for the underlying finite field operations should be implemented efficiently. Among these sub-modules, modular inversion (MI) requires the most computation; therefore, its performance might be a dominant factor of the overall performance of an ECC module. To determine the most efficient MI algorithm for an HW ECC module, we implement various classes of MI algorithms and analyze their performance. In contrast to the common belief in previous research, our results show that the right-shift binary inversion (RS) algorithm performs well when implemented in hardware. In addition, we present optimization methods to reduce the area overhead and improve the speed of the RS algorithm. By applying these methods, we propose a new RS-variant that is both fast and compact. The proposed MI module is more than twice as fast as the other two classes of MI: shifting Euclidean (SE) and left-shift binary inversion (LS) algorithms. It consumes only 15% more area and even 5% less area than SE and LS, respectively. Finally, we show that how our new method can be applied to optimize an HW ECC module.

• Nuclear Engineering and Technology
• /
• v.26 no.2
• /
• pp.205-211
• /
• 1994

The best method is selected among the 3 digital dynamic compensation methods which are developed or applied for the Rhodium self-powered neutron detector. The three digital dynamic compensation methods are the existing Dominant Pol Tustin method of the COLSS(Core Operating Limit Supervisory System), the Direct Inversion method and Kalman Filter method. The Direct Inversion method is an improved method of D. Hoppe and R. Maletti and the Kalman Filter method is developed using the Kalman Filter. Response times of the compensated signals to achieve 90% of a step input are 28.1, 17.2 and 6.5 seconds respectively for the same noise gain telling that the Kalman Filter method is the best amens the 3 methods.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.17 no.3
• /
• pp.20-25
• /
• 1980

A singular value decomposition (SVD) pseudo-inversion method has been applied to the image reconstruction from projections. This approach is relatively unknown and differs from conventionally used reconstructioll methods such as the Foxier convolution and iterative techniques. In this paper, two SVD pseudo-inversion methods have been discussed for the search of optimum reconstruction and restoration, one using truncated inverse filtering, the other scalar Wiener filtering. These methods partly overcome the ill-conditioned nature of restoration problems by trading off between noise and signal quality. To test the SVD pseudo-inversion method, simulations were performed from projection data obtained from a phantom using truncated inversefiltering. The results are presented together with some limitations particular to the applications of the method to the general class of 3-D image reconstruction and restoration.

• Geophysics and Geophysical Exploration
• /
• v.10 no.2
• /
• pp.138-146
• /
• 2007

This paper describes 2.5D induced polarization (IP) modeling and inversion algorithms using complex resistivity. The complex resistivity method has merits for acquiring more valuable information about hydraulic parameters and pore fluid than the conventional IP methods. The IP modeling and inversion algorithms are developed by allowing complex arithmetic in existing DC modeling and inversion algorithms. The IP modeling and inversion algorithms use a 2.5D DC finite-element algorithm and a damped least-squares method with smoothness constraints, respectively. The accuracy of the IP modeling algorithm is verified by comparing its responses of two synthetic models with two different approaches: linear filtering for a three-layer model and an integral equation method for a 3D model. Results from these methods are well matched to each other. The inversion algorithm is validated by a synthetic example which has two anomalous bodies, one is more conductive but non-polarizable than the background, and the other is polarizable but has the same resistivity as the background. From the inverted section, we can cleary identify each anomalous body with different locations. Furthermore, in order to verify its efficiency to the real filed example, we apply the inversion algorithm to another three-layer model which includes phase anomaly in the second layer.

• Geophysics and Geophysical Exploration
• /
• v.17 no.2
• /
• pp.95-103
• /
• 2014

This paper presents a practical inversion method for recovering a three-dimensional (3D) resistivity model and static shifts simultaneously. Although this method is based on a Gauss-Newton approach that requires a sensitivity matrix, the computer time can be greatly reduced by implementing a simple and effective procedure for updating the sensitivity matrix using the Broyden's algorithm. In this research, we examine the approximate inversion procedure and the weighting factor ${\beta}$ for static shifts through inversion experiments using synthetic MT data. In methods using the full sensitivity matrix constructed only once in the iteration process, a procedure using the full sensitivity in the earlier stage is useful to produce the smallest rms data misfit. The choice of ${\beta}$ is not critical below some threshold value. Synthetic examples demonstrate that the method proposed in this paper is effective in reconstructing a 3D resistivity structure from static-shifted MT data.

• Journal of the Korean earth science society
• /
• v.26 no.7
• /
• pp.691-697
• /
• 2005

Recently, the development of accurate gravity-meter and GPS make it possible to obtain high resolution gravity data. Though gravity data interpretation like modeling and inversion has significantly improved, gravity data processing itself has improved very little. Conventional gravity data processing removes gravity effects due to mass and height difference between base and measurement level. But, it would be a biased density model when some or whole part of anomalous bodies exist above the base level. We attempted to make a multiquadric surface of the survey area from topography with DEM (Digital Elevation Map) data. Then we constituted rectangular blocks which reflect real topography of the survey area by the multiquadric surface. Thus, we were able to carry out 3-D inversions which include information of topography. We named this technique, 3-D Gravity Terrain Inversion (3DGTI). The model test showed that the inversion model from 3DGTI made better results than conventional methods. Furthermore, the 3-dimensional model from the 3DGTI method could maintain topography and as a result, it showed more realistic geologic model. This method was also applied on real field data in Masan-Changwon area. Granitic intrusion is an important geologic characteristic in this area. This method showed more critical geological boundaries than other conventional methods. Therefore, we concluded that in the case of various rocks and rugged terrain, this new method will make better model than convention ones.

• Geophysics and Geophysical Exploration
• /
• v.7 no.3
• /
• pp.207-212
• /
• 2004

This article reviews recent developments in three-dimensional (3-D) magntotelluric (MT) imaging. The inversion of MT data is fundamentally ill-posed, and therefore the resultant solution is non-unique. A regularizing scheme must be involved to reduce the non-uniqueness while retaining certain a priori information in the solution. The standard approach to nonlinear inversion in geophysis has been the Gauss-Newton method, which solves a sequence of linearized inverse problems. When running to convergence, the algorithm minimizes an objective function over the space of models and in the sense produces an optimal solution of the inverse problem. The general usefulness of iterative, linearized inversion algorithms, however is greatly limited in 3-D MT applications by the requirement of computing the Jacobian(partial derivative, sensitivity) matrix of the forward problem. The difficulty may be relaxed using conjugate gradients(CG) methods. A linear CG technique is used to solve each step of Gauss-Newton iterations incompletely, while the method of nonlinear CG is applied directly to the minimization of the objective function. These CG techniques replace computation of jacobian matrix and solution of a large linear system with computations equivalent to only three forward problems per inversion iteration. Consequently, the algorithms are efficient in computational speed and memory requirement, making 3-D inversion feasible.

• Geophysics and Geophysical Exploration
• /
• v.8 no.2
• /
• pp.170-176
• /
• 2005

Recently the velocity stack inversion is having many attentions as an useful way to perform various seismic data processing. In order to be used in various seismic data processing, the inversion method used should have properties such as robustness to noise and parsimony of the velocity stack result. The IRLS (Iteratively Reweighted Least-Squares) method that minimizes ${L_1}-norm$ is the one used mostly. This paper introduce another method, CGG (Conjugate Guided Gradient) method, which can be used to achieve the same goal as the IRLS method does. The CGG method is a modified CG (Conjugate Gradient) method that minimizes ${L_1}-norm$. This paper explains the CGG method and compares the result of it with the one of IRSL methods. Testing on synthetic and real data demonstrates that CGG method can be used as an inversion method f3r minimizing various residual/model norms like IRLS methods.