• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2010.04a
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• pp.197-199
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• 2010

A gravity survey is a base of research earth gravity field determined, perception of the vertical motion, change of Geoid, sea-level changes, climate change etc. Recently, FG-5 was adopted in NGII. NGII has completed 4 points of absolute gravity survey and 1,400 points of relative gravity survey in 2009 to aim to observe 20 points of absolute gravity survey and 6,000 points of gravity control point by 2013. Using results of gravity survey, NGII will provide citizen with data for research about renewal of geoid model and geophysics. This study aims to go over examples of utilization of absolute gravimeter & method of utilization in korea.

• Economic and Environmental Geology
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• v.28 no.1
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• pp.79-88
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• 1995

The gravity measurment has been carried out at 48 gravity stations with intervals of 1.0~1.5 km along the survey line between Samcheog, Gosari and Taebaek to study subsurface geology and geologic structure in the northeastern part of the Ockchon zone. The Bouguer gravity anomaly values were obtained from the measured gravity values through the gravity corrections. The subsurface geology and geologic structure were interpreted quantitatively by means of the Fourier series method and Talwani method for 2.5 dimensional body. In the study area, the depth of Conrad discontinuity is about 10 km at Samcheog, northeastern end of the survey line, and it is increased rapidly to about 12.5 km at Miro, 15 km at Gosari and 15.5 km at Dongjeom, southwestern end of the survey line, respectively. The depth of the basement of the Ockchon zone exposed at Samcheog is increased smoothly to about 2 km at 5 km from Samcheog along the survey line, and is exposed again in the area between Singiry and Gosari. Beyond Gosari its depth is increased to about 1.7 km, and displaced 2.3 km downward by Osipcheon fault near Dogyeri and 0.5 km by Baeksan thrust near Cheolam, respectively. Many V-shaped low Bouguer gravity anomalies resulted from the fracture zone associated with faults imply the existence of Osipcheon fault and several inferred faults. The low Bouguer gravity anomaly zone between Tongdong and Dongjeom is caused by Jurassic gneissose granite. A local high Bouguer gravity anomaly at 35 km along the survey line from Samcheog is interpreted by the effect of iron deposit of high density existed at subsurface. The thickness of Great Limestone Group varies from 0.5 km to 1.4 km, that of Pyeongan Supergroup from 0.4 km to 0.9 km, and that of Yangdeog Group is about 0.3 km. The thickness of Jurassic gneissose granite varies from 1.5 to 3.0 km.

• Geophysics and Geophysical Exploration
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• v.13 no.1
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• pp.88-95
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• 2010

An airborne gravity survey using a helicopter was carried out in October 2008, offshore along the northern Noto Peninsula, to understand the shallow and regional underground structure. Eleven flight lines, including three tie lines, were arranged at 2 km spacing within 20 km of the coast. The total length of the flight lines was ~700 km. The Bouguer anomalies computed from the airborne gravimetry are consistent with those computed from land and shipborne gravimetry, which gradually decrease in the offshore direction. So, the accuracy of the airborne system is considered to be adequate. A local gravity low in Wajima Bay, which was already known from seafloor gravimetry, was also observed. This suggests that the airborne system has a structural resolution of ~2 km. Reduction of gravity data to a common datum was conducted by compiling the three kinds of gravity data, from airborne, shipborne, and land surveys. In the present study, we have used a solid angle numerical integration method and an iteration method. We finally calculated the gravity anomalies at 300 m above sea level. We needed to add corrections of 2.5 mGals in order to compile the airborne and shipborne gravity data smoothly, so the accuracy of the Bouguer anomaly map is considered to be nearly 2 mGal on the whole, and 5 mGals at worst in limited or local areas.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.267-272
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• 2007

Uiseong subbasin belonging to Kyungsang basin resulted from volcanic activity in the late Cretaceous. In this study, we carry out MT and gravity survey at the Hwasan caldera, which was formed of volcanic and abyssal rocks complex, then analyze and identify geological substructure. Potential survey such as gravity and magnetic survey has been mainly carried out in former studies, so depth information for understanding substructure was not enough. To complement a potential survey, we use MT method, which has high vertical resolution. Moreover we make a simple 2D model comparing with former study. The result of MT and gravity 2D modeling shows that this area is roughly composed of 3 layers; The bottom layer is a basement. In the second layer, intrusive rocks having high resistivity is placed along the ring faults and the sedimentary layer of low resistivity is inside caldera. The highest layer is alluvium. To comprehend the 3D structure of the Hwasan caldera, we perform 3D gravity inversion, and construct the 3D model from the result of 3D gravity inversion. MT responses are calculated by using the constructed 3D model and the 3D model of the Hwasan caldera's structure is suggested after comparing the calculated values with the observed values at MT line.

• Economic and Environmental Geology
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• v.24 no.1
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• pp.63-69
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• 1991

Gravity study was carried out to investigate the structure and total mass of the Bupyeong silver deposits closely related to formation of the Bupyeong caldera. Survey region covers $3.3{\times}6.6km^2$ over silver deposits and is comprised of 334 gravity measurement stations. An apparent regional gravity trend parallel to the west coast line is mainly attributed to isostasy. A least square isostasy model was used for the regional correction. A Fortan subroutine was coded to calculate 3-dimensional subsurface model. The calculated gravity values from the 3-dimensional model of the caldera with silver deposits agree with observed anomalies relatively well. Gravity anomaly due to Bupyeong silver deposits reaches to +3.5 mgal from the background value and anomaly due to the caldera reaches to -4 mgal. But the maximum negative anomaly of the caldera would be much greater at its center. The total mass of silver deposits calculated from the subsurface model is $4.19{\times}10^9$ tons. Although the economic part of silver deposits depends on the grade of orebody, we expect that there are still large amount of silver reserves in Bupyeong area.

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

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.62.2-62.2
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• 2018

From the gaussian, near scale-invariant density perturbations observed in the CMB to the late time clustering of galaxies, CDM provides a minimal theoretical explanation for a variety of cosmological data. However accepting this explanation, requires that we include within our cosmic ontology a vacuum energy that is ~122 orders of magnitude lower than QM predictions, or alternatively a new scalar field (dark energy) that has negative pressure. Alternatively, modifications to Einstein's General Relativity have been proposed as a model for cosmic acceleration. Recently there have been many works attempting to test for modified gravity using the large scale clustering of galaxies, ISW, cluster abundance, RSD, 21cm observations, and weak lensing. In this work, we compare various modified gravity models using cosmic shear data from the Deep Lens Survey as well as data from CMB, SNe Ia, and BAO. We use the Bayesian Evidence to quantify the comparison robustly, which naturally penalizes complex models with weak data support. In this poster we present our methodology and preliminary constraints on f(R) gravity.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2009.04a
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• pp.49-53
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• 2009

In this study, point gravity was measured to achieve terrestrid gravity data and the gravity is important element in precise geoid modelling. Surveys the relative gravity of 56 stations on 1st level route. In addition, it calculates gravity values, analysis gravity survey results using tidal correction, drift correction, datum-free adjustment. These point gravity data could be contribute in development of precise geoid model.

• Economic and Environmental Geology
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• v.32 no.6
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• pp.645-651
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• 1999

The gravity and magnetic measurements have been obtained from 34 stations with 50m intervals along the survey line positioned between Jangtanri and sindapri for studying subsurface geology and structures of the volcanic rocks in Yeoncheon area. The Bouguer gravity and magnetic anomaly values were evaluated from the reduction of the field observation, and then interpreted by Nettleton's method and maximum-pepth rules, are approximately 160m based on magnetic data and 135m based on gravity data. High Bouguer gravity anomaly zone between 0m in Jangtanri and 900m along the survery line, is caused by thick and high density, older dasalt which is positioned beneath jijangbong tuff breccia, and this result corresponds to the interpretation result based on magnetic anomly. Lower gravity and magnetic anomaly zones ariund 900m are caused by between 1300m and 1550m are caused by high density of Quarternary basalt exposed in the surface, and lower gravity and magnetic anomalies at 200m and 1250m are caused by faults.

• Korean Journal of Remote Sensing
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• v.17 no.4
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• pp.297-305
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• 2001

Ocean satellite altimetry-implied free-air gravity anomalies have had the shortest wavelengths removed during the processing to generate the optimal solution between multiple radar altimeter missions. ERS-1 168day mission altimetry was residualized to a reference geoid surface generated by integrating Anderson & Knudsen’s free-air gravity anomalies for the Barents Sea. The altimetry tracks were reduced and filtered to extract the shortest wavelengths (between 4 and 111 km) from both ascending and descending tracks, respectively. These data were recombined using existing quadrant-swapping techniques in the wavenumber domain to generate a correlated, high frequency gravity field related to the local geologic sources. This added-value surface adjusted the reference free-air gravity anomalies to better reflect features in the gravity field at a wavelength related to the distance between altimetry ground tracks.