• Journal of the Korea Institute of Information and Communication Engineering
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• 제15권9호
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• pp.1833-1839
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• 2011

In this study, Global Gravitational Model EGM2008, EGM96 and 16,786 gravity points measured on land were compared and analyzed. On the assumption that land gravity data is most accurate, the correlation coefficient, differences, MSE and difference variance along the height were computed between land gravity data and EGM2008, EG96. The correlation coefficient, land gravity data and EGM2008, was computed most largely with 0.824 and the correlation coefficient with EGM96 was computed with 0.538. The standard deviation of differences between land gravity and EGM2008, EGM96 were 13.196 magl, 18.685 mgal respectively. Also the difference variance scope of EGM2008 was smaller than EGM96. There was no large variance of free-air anomaly differences between land gravity data and EGM2008 along the height however free-air anomaly differences with EGM96 varied along the height changes. Consequently EGM2008 nicely expresses Korea gravity field more than EGM96.

• Geophysics and Geophysical Exploration
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• 제26권1호
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• pp.1-7
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• 2023

This study derives the expressions of vector gravity and gravity gradient tensor due to an elliptical cylinder. The vector gravity for an arbitrary three-dimensional (3D) body is obtained by differentiating the gravitational potential, including the triple integral, according to the shape of the body in each axis direction. The vector gravity of the 3D body with axial symmetry is integrated along the axial direction and reduced to a double integral. The complex Green's theorem using complex conjugates subsequently converts the double integral into a one-dimensional (1D) closed-line integral. Finally, the vector gravity due to the elliptical cylinder is derived using 1D numerical integration by parameterizing a boundary of the elliptical cross-section as a closed line. Similarly, the gravity gradient tensor due to the elliptical cylinder is second-order differentiated from the gravitational potential, including the triple integral, and integrated along the vertical axis direction reducing it to a double integral. Consequently, all the components of the gravity gradient tensor due to an elliptical cylinder are derived using complex Green's theorem as used in the case of vector gravity.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• 제27권2호
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• pp.139-147
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• 2009

The gravity data collected and reserved in Korea is seriously biased in its distribution. That is, only the west-southern part of the peninsula including Chungcheong and Jeonla area has dense distribution while only a part is covered in Gyoungsang area. Especially, the low density of the gravity data in mountainous area basically limits the accuracy of the gravimetric geoid in Korea. As one of the solution to overcome the problem, an airborne gravity survey were conducted from Dec. 2008 $\sim$ Jan. 2009. In this study, free-air gravity anomaly derived from the airborne gravity data which has consistent quality are presented. The data processing for the airborne gravity is composed of several corrections of errors such as errors from gravity measurement, errors from flight dynamics, errors from GPS, and errors from time synchronization. We presented detailed explanations on the data processing with the final cross-over results. The free-air anomaly from airborne gravity finally shows the cross-over accuracy of 2.21mGal which reflects the precision of each track is 1.56mGal. It is expected that the result from this study will play a role as input data in precision geoid determination with ground and ship-borne gravity data after appropriate fusion process.

• Economic and Environmental Geology
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• 제48권6호
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• pp.451-465
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• 2015

The free-air anomalies are computed using a data set from various types of gravity measurements in the Korean Peninsula area. The gravity values extracted from the Earth Gravitational Model 2008 are used in the surrounding region. The upward continuation technique suggested by Dragomir is used in the computation of the external free-air anomalies at various altitudes. The integration radius 10 times the altitude is used in order to keep the accuracy of results and computational resources. The direct geodesic formula developed by Bowring is employed in integration. At the 1-km altitude, the free-air anomalies vary from -41.315 to 189.327 mgal with the standard deviation of 22.612 mgal. At the 3-km altitude, they vary from -36.478 to 156.209 mgal with the standard deviation of 20.641 mgal. At the 1,000-km altitude, they vary from 3.170 to 5.864 mgal with the standard deviation of 0.670 mgal. The predicted free-air anomalies at 3-km altitude are compared to the published free-air anomalies reduced from the airborne gravity measurements at the same altitude. The rms difference is 3.88 mgal. Considering the reported 2.21-mgal airborne gravity cross-over accuracy, this rms difference is not serious. Possible causes in the difference appear to be external free-air anomaly simulation errors in this work and/or the gravity reduction errors of the other. The external gravity field is predicted by adding the external free-air anomaly to the normal gravity computed using the closed form formula for the gravity above and below the surface of the ellipsoid. The predicted external gravity field in this work is expected to reasonably present the real external gravity field. This work seems to be the first structured research on the external free-air anomaly in the Korean Peninsula area, and the external gravity field can be used to improve the accuracy of the inertial navigation system.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• 제14권2호
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• pp.127-139
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• 1996

This paper presents a procedure to recover sea surface heights (SSH) and free-air (FA) gravity anomalies from dense satellite altimeter SSH data with enhanced accuracies over the full spectrum of the gravity field. A wavenumber correlation filtering (WCF) of co-linear SSH tracks is developed for the coherent signals of sub-surface geological masses. Orbital cross-over adjustments with bias parameters are applied to the filtered SSH data, which are then separated into two groups of ascending and descending tracks and gridded with tensioned splines. A directional sensitive filter (DSF) is developed to reduce residual errors in the orbital adjustments that appear as track patterned SSH. Finally, FA gravity anomalies can be obtained by the application of a gradient filter on a high resolution estimate of geoid undulations after subtracting dynamic sea surface topography (DSST) from the SSH. These procedures are applied to the Geosat Geodetic Mission (GM) data of the southern oceans in a test area of ca. $900km\;\times{1,200}\;km$ to resolve geoid undulations and FA gravity anomalies to wavelengths of-10 km and larger. Comparisons with gravity data from ship surveys, predictions by least squares collocation (LSC), and 2 versions of NOAA's predictions using vertical deflections illustrate the performance of this procedure for recovering all elements of the gravity spectrum. Statistics on differences between precise ship data and predicted FA gravity anomalies show a mean of 0.1 mgal, an RMS of 3.5 mgal, maximum differences of 10. 2 mgal and -18.6 mgal, and a correlation coefficient of 0.993 over four straight ship tracks of ca. 1,600 km where gravity changes over 150 mgals.

• Journal of the Korean earth science society
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• 제32권1호
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• pp.12-20
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• 2011

The gravity measurement was conducted at 256 stations around Chungju Lake to study subsurface geological distributions and subterranean mass discontinuities by the results of gravity anomaly in Metamorphic Complex, Okcheon Group, Great Limestone Group of Choson Supergroup, and Cretaceous biotite granites. Okcheon Group showed a high Bouguer gravity anomaly while Great Limestone Group of Choson Supergroup relatively a low anomaly. The mean depth of subterranean mass discontinuities is about 2.0 km and downward along the Suchangri Formation from the Hwanggangri and Moonjuri formations. In general, Okcheon Group appeared shallower than the depth of Great Limestone Group of Choson Supergroup when imaging the subterranean mass discontinuities from the Bouguer gravity anomaly.

• Journal of the Korean earth science society
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• 제35권7호
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• pp.529-536
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• 2014

In this paper, the automatic determination algorithm of strike and dip of a line source using gravity gradient on a single profile is proposed. In general, the gravity gradient tensor due to a line source has only two independent components because of its 2-Dimensional (2-D) characteristics. However, if the line source has the strike and dip regarding the observation profile, it comes to have five independent components. The proposed algorithm of the determination both strike and dip is based on the rotational transform that converts full gravity gradient tensor to reduced 2-D gravity gradient tensor. The least-square method is applied in order to find optimum rotational angles that make one of the row components minimalized simultaneously. The two synthetic cases of a line source are represented; one has strike only and the other has both strike and dip. This study finds that the automatic determination method using gravity gradient tensor can find directions of a line source in each case.

• Economic and Environmental Geology
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• 제55권5호
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• pp.521-529
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• 2022

Gravity exploration was conducted to determine the distribution of igneous complex related to lithium pegmatite in the Boam deposit of Uljin, Gyeongsangbuk-do, and the spatial relationship with the regional geology and ore bodies were studied. The gravity exploration result shows that the Boam deposit area is characterized by relatively low gravity anomaly that surrounds the deposit. The Boam deposit is located near the southwest-northeast directional boundary of gravity anomalies where igneous complex (granite gneiss) contacts with the Yuli and Wonnam groups in the southeast, Janggun limestone layers in the east-west direction, and Dongsugok metasedimentary rocks. While the western boundary in the southwest-northeast direction is relatively clear, there may also be unknown igneous complex that are not exposed on the surface at the eastern and southern boundaries because a relatively low gravity anomaly surrounds the deposit. The distribution characteristics of these hidden igneous complex will be used as useful data for predicting the distribution of the lithium pegmatite in the future.

• The Journal of Engineering Geology
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• 제8권3호
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• pp.285-296
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• 1998

As a part of the study for understanding the deep geological structure of the Ogcheon Zone, both gravity and geomagnetic surveys are performed. A 70km survey line of which direction is nearly perpendicular to major faults in the southern tip of the Zone. The observed data are corrected and transformed into Bouguer and total magnetic intensity anomalies, respectively. Recent studies for petrology and geochemistry in the southwestern Ogcheon Zone in the vicinity of the survey line are reviewed for better interpretation. Both gravity and geomagnetic anomalies abruptly change around Janghung area, the southern boundary of the, Ogcheon Zone. This rapid increase of Bouguer anomaly around Janghung area can be explained by a deep seated normal fault with fairy large displacement between Precambrian gneisses and the denser intermediate plutonic rocks. It is believed that the fault acted an important role for the formation and evolution of the Ogcheon Zone. A pseudomagnetic intensity anomaly is calculated from the Bouguer anomaly assuming that the both anomalies are associated with the common source. From the origin of the survey line to the 50km point, the calculated anomaly coincides with observed magnetic anomaly. Whereas both anomalies show negative correlation in the outside 50km. From the residual Bouguer anomalies, the subterranean geological structure is provided through the iterative forward method. The initial model is obtained from informations about the surface geology as well as the results of the inverse method.

• Journal of the Korean Geophysical Society
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• 제2권1호
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• pp.27-38
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• 1999

The errors between track segments or at the cross-over points of shipborne gravity were successfully reduced by applying a cross-over error adjustment technique using satellite gravity. The integration of shipborne and satellite altimeter-implied free-air gravity anomalies after the cross-over error adjustment resulted in a high resolution gravity map which contains both short and long wavelength components. The successful adjustment of the cross-over errors in the shipborne gravity using the satellite gravity suggests that the shipborne gravity can be combined with the satellite anomalies characterized by a stable and long wavelength component. The resulting free-air anomaly map is evenly harmonized with both short and long wavelength anomalies. Thus the corrected anomaly map can be better used for the geological interpretation. Free-air anomalies with more than 140 mGal in total variations generally correspond to the seafloor topographic changes in their regional patterns. A series of gravity highs are aligned from the Korea Plateau to the Oki Island, which are interpreted to be caused by seamounts or volcanic topographies. The gravity minima along the western and southern shelf edge are associated not only with the local basement morphology and thick sediment fill at the continental margin, but also possibly with the crustal edge effect known for passive continental margins. Series of NE-trending linear anomalies are possibly caused by a swarm of volcanic intrusions followed the initial opening of the Ulleung Basin. The linear high anomalies in the Ulleung Plateau are terminated by the straightly NNW-trending anomalies with a sharp gradient in its western boundary which indicates a fault-line scarp. The opposite side adjoined with the fault-line scarp shows no correlation with the fault-line scarp in geometry indicating that the block might be horizontally slided from the north. A gravity high in contrast to the deepening in seafloor toward the northeastern central Ulleung Basin is probably responsible for the thin crust and shallow seated mantle. The gravity minima along the western and southern shelf edge are associated not only with the local basement morphology and thick sediment fill at the continental margin, but also possibly with the crustal edge effect known for passive continental margins. Series of NE-trending linear anomalies are possibly caused by a swarm of volcanic intrusions followed the initial opening of the Ulleung Basin. The linear high anomalies in the Ulleung Plateau are terminated by the straightly NNW-trending anomalies with a sharp gradient in its western boundary which indicates a fault-line scarp. The opposite side adjoined with the fault-line scarp shows no correlation with the fault-line scarp in geometry indicating that the block might be horizontally slided from the north. A gravity high in contrast to the deepening in seafloor toward the northeastern central Ulleung Basin is probably suggestive of a thin crust and shallow seated mantle.