• Economic and Environmental Geology
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• v.28 no.6
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• pp.553-558
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• 1995

The purpose of this paper is recovery of the profiles of the wave speed and density from the reflection coefficients of the continuously layered acoustic medium with depth dependent density and wave speed at various angles of incidence. A downward continuation or layer stripping algorithm, which recursively reconstructs the medium in increasing depth and then strips away the effects of the reconstructed portion of the medium, is the method with fewer computations than integral equation procedures. This paper implements an improved downward continuation algorithm that uses reflection data at several angles of incidence and performs a least-squares fitting at each depth. The result is a considerable improvement in performance over the usual downward continuation algorithm.

• Economic and Environmental Geology
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• v.43 no.3
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• pp.249-258
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• 2010

In general, a crustal geomagnetic (or gravity) anomaly compiled at one altitude can be estimated at a different altitude by continuation using the Fourier transform (FT). However, in case of continuation with a great distance between the two elevations, or, in particular, in case of downward continuation, the estimated anomalies by the FT are likely to be mathematically unstable so that the estimated values are not realistic. To solve this problem, two independently measured magnetic field anomalies at different altitudes, such as aeromagnetic and satellite magnetic observations, are implemented to estimate values at in-between altitude for better understanding and interpreting geophysical and geological features. This ‘'dual continuation’' technique is straightforward in the FT and gives a more realistic estimate in all altitudes when we simulated with a set of prismatic bodies at different altitudes. This implies that we add up another constraint like satellite-based observations on the geopotential field modeling for the non-unique geological and geophysical problems to a conventional Fourier-type continuation technique with a single set of observations.

• Geophysics and Geophysical Exploration
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• v.16 no.1
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• pp.59-62
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• 2013

We formerly reported a new method for the upward continuation of potential field on spherical patch area including Earth's curvature, which has been neglected in most studies on rectangular area with flat Earth assumption. This new method is applicable to downward continuation as well by only assigning corresponding value for the ratio of two radii; $r_2/r_1$, i.e., target radius $r_2$ versus datum radius $r_1$. In addition, the inherent problem of this method due to spherical surface geometry is described, and its one possible remedy is given.

• Economic and Environmental Geology
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• v.23 no.3
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• pp.353-358
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• 1990

This paper presents numerical experiments on migration of synthetic seismograms using by $45^{\circ}$ wave equation. The seismograms used are zero-offset seismogram (corresponding to stacked section) on point reflectors, dipping plane reflector, faulted and folded layers. The seismograms are constructed by upward continuation of seismic source wavelets, exploading on subsurface reflection interfaces, to the earth surface. The synthetic seismograms are migrated by downward continuation and imaging. The upward and downward continuations are implemented by solving the $45^{\circ}$ wave equation with the finite-difference method. Migration of the synthetic data used in this study results in relatively accurate reposition of subsurface structures while the synthetic sections are quite different from the structures.

• 한국지구물리탐사학회:학술대회논문집
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• 2011.10a
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• pp.177-178
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• 2011

• Economic and Environmental Geology
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• v.14 no.2
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• pp.93-102
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• 1981

Studies of model potential fields continued upward and downward show differences depending on the method of continuation. Beginning with a magnetic field computed over a buried vertical cylinder, the field was continued to various levels by a method introduced by Henderson (Lagrangian interpolation) and by a spectral method (frequency domain analysis). Resultant fields show (1) no significant differences in upward continued values, (2) in downward continuation, accurate values are obtained with the spectral method over the central part of the anomaly, and (3) accurate values are obtained with Henderson's method on the flanks of the anomaly, while oscillations usually characterize the spectral method in this region. Essentially the same observations are made for derivative calculations. Field oscillations are empirically predicted at levels continued to approximately two-thirds of the depth of the source. Our spectral computer program output yields marked oscillations at one-half of the depth of the source. Henderson's method shows no oscillations at this depth and only minor oscillations at the top of the body (some negative values appear on the flanks of the anomaly). The Henderson output is a smooth field even if continued below the top of the body. These results suggest that the presence of oscillations cannot be used to identify the top of a buried source without careful consideration of the method used to continue the field. Use of the derivative to outline and isolate anomalies must similarly include consideration of the method of calculation.

• Journal of Advanced Navigation Technology
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• v.13 no.2
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• pp.257-261
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• 2009

This paper propose a new method using Gestalt theory to extract image contour. The proposed method use Gestalt theory based on proximity, similarity and continuation for grouping objects from image segmentation. It use downward feedback and perception to materialize one visual level in image from heterogeneity visual levels in image. The experimental result show that the proposed method achieves better performance than other methods.

• Spatial Information Research
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• v.17 no.3
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• pp.397-404
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• 2009

To solve the problems of distribution and quality on land gravity data, airborne gravity survey was performed in 2008 obtaining the airborne gravity data with accuracy of 1.56mGal. Since airborne gravity data is the obtained at the flight height, it is necessary to convert the airborne gravity data to the surface to combine various gravity data and compute precision geoid. In addition, Stokes' integral radius, Stokes' kernel and the radius of terrain effect computation should be optimally determined to calculate precision geoid. In this study, we made an effort to decide the optimal parameters based on the distribution and the characteristic of gravity data. Then, two geoid models were calculated using the selected parameters and the difference of geoid was calculated with mean of -16.95cm and the standard deviation of ${\pm}8.50cm$. We consider that this difference is due to the distribution and errors on the gravity data. For future work, the study on the effect of geoid with newly obtained land gravity data ship-borne gravity data and GPS/Leveling data should be conducted. Furthermore, the study on the downward continuation and terran effect calculation should be studied in detail for better precision geoid construction.

• Journal of the Korean Institute of Landscape Architecture
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• v.32 no.1
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• pp.33-46
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• 2004

This study is aimed to redesign established parks and to propose a series of devices protecting them from vandalism. To solve the problems, we ascertained the damaged areas of the park greens. The trace analysis was performed to grasp the transverse inside the parks of Jeonju and Iksan in Collabuldo. Then, we presented the basic plan for minimizing park damage and for remodeling the system of movement. The results of the study are summarized as follows: it is identified that the transverse phenomenon is considerably wide-spread in majority of parks, and has no relationship to the park area or the green area. It is considered that the $\ulcorner$Condition rating class$\lrcorner$ of grass damage, which is grade 6, is extraordinarily high and the damage is accumulated considerably. Also, the damage part of other grade is discovered equally, and when unattended, the acceleration of damage is positive. A damage width a 0.5∼1.5m makes up the greater part of 79.6%. It also constitutes most of a rectilinear form. The difference in the height between the original point and destination point is below 0.7m, which is above 70%. It is identified that the interrelationship between the damage continuation length and plan distance is relatively high by the simple regression: analysis and by Pearson' correlation analysis. In spite of the normal damage continuation length is 20m, the frequency degree is downward with extreme point at 10m. Accordingly, it is assumed that park users have physical and psychological pressure when they cross the lawn field. Damage types are classified as the Simple cut cross type, the Behavioral facilitates type, Access advantage type and the Strolling type through type classification. It is considered that this classification is effective when identifying short pass type on lawn field according to the damage length and intensity.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.33 no.3
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• pp.181-192
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• 2015

Bathymetry change due to the 2011 Tohoku (M9.0) earthquake was investigated through satellite altimetry-derived free-air gravity anomalies (SAFAGA) and shipborne measurements. The earthquake occurred at the plate boundaries near the northeastern coast of Japan, where the oceanic plate subducts beneath the continental plate along deep-sea trench. Data analyzed in this study include SAFAGA from Scripps Institution of Oceanography (SIO), shipborne bathymetry (SB) from the U.S. National Geophysical Data Center (NGDC) and the Japan Agency for Marine-Earth-Science And Technology (JAMSTEC). To estimate the bathymetry change, a reference bathymetry before the earthquake was predicted by gravity-geologic method (GGM) and Smith & Sandwell’s (SAS) method. In comparison with the bathymetry models before the earthquake, GGM bathymetry model generated by a tuning density contrast of 17.04 g/cm³ by downward continuation method was selected because it shows better bathymetry in the short wavelength below about 6 km. From the results, remarkable bathymetry change of about ±50 m was found on the west side of the Japan Trench caused by the earthquake.