• 한국해양학회지
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• v.22 no.1
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• pp.19-24
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• 1987

Gravity measurements at sea are considered to be made on the geoid. The free-air anomalies are then determined by subtracting the theoretical gravity values predicted on a reference ellipsoid from the observed values. The gravity effect due to the height difference between the geoid and reference ellipsoid and the mass between them is known as the 'indirect effect'. The result of applying the indirect effect to surface ship derived gravity anomalies in the North Atlantic Ocean demonstrates the importance of its inclusion for regional stuedies involving mantle processes.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.4
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• pp.393-403
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• 2011

In this study, we suggested the period of tide observations is proper to calculate the mean sea level(MSL) precisely on Incheon tide station using wavelet analysis, and newly determined then the vertical reference surface of Korea using the calculated MSL. In order to calculate the height difference between the calculated MSL and specific ground station (ICGP) near the Incheon tide stations, we performed the laser measurements directly to the sea surface where located below ICGP. The orthometric-height of ICGP was determined that corrected the height difference to the calculated MSL using linear interpolation method. Finally, we connected the orthometric-height of ICGP with the original benchmark (ORBM) using GPS leveling methods for determining the new orthometric-height of ORBM. As the results, there is a variation amount of 0.026m between the new MSL was calculated in this study and old MSL was calculated in 1910's. Also, there is a difference of 0.035m between the new and old orthometric-heights of ORBM. The connection (or leveling) error of 0.009m was revealed in new orthometric height of ORBM with consideration of MSL variation which may caused by the error of GPS ellipsoid height and/or geoid model. In this study, we could be determined precisely the orthometric-height of ORBM based on the new MSL of Incheon Bay using only GPS leveling method, not a spirit leveling method. Therefore, it is necessary to determine the vertical datum strictly using long-term and continuously tide observations more than 19 years and to use the GPS leveling method widely in the height leveling work for the effective changeover from the orthonormal to the orthometric in national height system.

• Journal of the Korean earth science society
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• v.18 no.6
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• pp.522-528
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• 1997

Gravity surveys with accompanying spirit levelings were carried out in Mt. Hangye area. From these survey results, orthometric height correctioins were calculated. The correction reaches 5 cm when the height difference is 900 m in this area. The corrections were also calculated using an available Bouguer anomaly map, and they are little different from the previous results. In conclusion, orthometric height corrections are necessary in precise spirit leveling, specially in higher lands, and they can be easily calculated from an available Bouguer anomaly map without laborious gravity surveys.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.13 no.2
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• pp.153-162
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• 1995

The coordinate transformation both WGS84 and Bessel ellipsoids is essential to use of GPS in South Korea. Especially, for transformation considered the needed accuracy and the regional characteristics, the study about geoid modeling and the characteristics on the transformed area should be done. The aim of this study define the characteristics of the transformed coordinates according to transformation methods and the area measured by GPS. For this, large network that include South Korea, four regional network consist of large network, and local net-work include Incheon city designed. Geoid model based on Bessel suitable to South Korea selected from study about the effects of the assumed geoid height at the geodetic origin, and then coefficients computed according as transformed area and methods. Also, the transformed characteristics of the large coefficients, the regional coefficients, and the local coefficients according to methods compared, analyzed synthetically.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.4
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• pp.379-386
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• 2008

To determine the precise geoid, the quality land gravity data as well as the accurate position information of the observation points are required. Here, the land gravity data should be processed in a consistent way from the raw data level producing the quality free-air anomaly being used in the geoid determination. In this study, we processed land gravity data of KIGAM(Korea Institute of Geoscience and Mineral Resources) and Pusan national university which has precise position information acquired from GPS and raw gravity data. The conversion from readings of gravimeter to the gravity value, corrections of instrumental height and tide were carried out from the raw gravity data for each surveying session. Then, a cross-over adjustment was applied to generate a free-air anomaly for whole data with precision of 0.48 mGal. It is expected that the data processed through this study shall be a foundation on the determination of the precise geoid model in Korea.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.20 no.4
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• pp.383-388
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• 2002

This study suggests a data processing method for precise geoid height calculation through sea gravity data of mid-Yellow Sea provided by Haeyang 2000 and satellite altimetry data and the EGM96 geopotential model from GSFC/DMA in USA. Also it compared sea gravity data with satellite altimetry gravity data. As a result, precise geoidal undulation of the mid-Yellow Sea presented from calculating and integrating EGM96 geopotential model in degree and order 167 and a relative geoid by integral radius of 27km respectively It has a mean value of 18.339m, varying from 13.564m to 22.785m. the comparison between sea gravity data and satellite altimetry data shows that the former is more precise than the latter, which showed an anomaly of 0.56m0Gal and RMSE of 4.195m.

• Journal of Positioning, Navigation, and Timing
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• v.5 no.4
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• pp.221-233
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• 2016

This paper deals with performance assessment of the kinematic network-based GPS positioning technique with a view to using it for ellipsoidally referenced bathymetric surveys. To this end, two field trials were carried out on a land vehicle and a surveying vessel. Single-frequency GPS data acquired from these tests were processed by an in-house software which equips the network modeling algorithm with instantaneous ambiguity resolution procedure. The results reveals that ambiguity success rate based on the network model is mostly higher than 99.0%, which is superior to that of the single-baseline model. In addition, achievable accuracy of the technique was accessed at ${\pm}1.6cm$ and 2.7 cm with 95% confidence level in horizontal and vertical component respectively. From bathymetric survey at the West Nakdong River in Busan, Korea, 3-D coordinates of 2,011 points on its bed were computed by using GPS-derived coordinates, attitude, measured depth and geoid undulation. Note that their vertical coordinates are aligned to the geoid, the so-called orthometric height which is widely adopted in river engineering. Bathymetry was constructed by interpolating the coordinate set, and some discussion on its benefit was given at the end.

• Journal of Korean Society for Geospatial Information Science
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• v.10 no.2 s.20
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• pp.107-114
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• 2002

This study aimed to estimate accuracy of GPS/Leveling and to present availability of GPS/Leveling in public surveying. For this purpose, we carried out GPS survey for bench marks and control points of Hongsung area. Orthometric heights calculated by two GPS/Leveling methods were compared to reference height. The one is calculated by base of geoid models such as EGM96, OSU91A, KGEOID99, and the other is calculated by network adjustment using fixed point. The results of GPS/Leveling by geoid models show that RMSE of EGM96 is ${\pm}0.061m,\;OSU91A\;{\pm}0.725m,\;KGEOID99\;{\pm}0.598m$. The results of GPS/Leveling by network adjustment show that the best RMSE is ${\pm}0.043m$ in case of using three fixed bench mark, and this method can be used for leveling effectively. GPS/Leveling would be able to apply in forth order public leveling and height determination of public control points.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1D
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• pp.161-166
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• 2009

High-resolution, high-precision ultra-high degree earth gravitational model are significant for the development of geodesy, geophysics, geodynamics and oceanography. In this research, we introduces the ultra-high earth gravitational model EGM2008 recently announced by U.S. NGA, reviews the issues and status of the ultra-high degree gravitational model development, and analyzes the accuracy of the gravitational model in Korea. First, EGM2008 is compared with the gravitational model EGM96 and Korea high-precision hybrid geoid model KGEOID08. In addition, the absolute accuracy is evaluated by ellipsoid height and orthometric height of a satellite geodetic reference point. Overall, the results show a similar accuracy between EGM2008 and KGEOID08. Thus, EGM2008 will be helpful for the future development of regional geoid and analysis of global gravity field.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.12 no.1
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• pp.69-76
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• 1994

In this paper, the characteristics of coordinate transformation between the WGS84 and the Bessel ellipsoids according to the assumed values of the geoidal height on Bessel ellipsoid at the geodetic datum origin of Korea were investigated. For this, based on GPS data of 11 control points in Chungnam and Chungbuk province, the mean shift values between ellipsoids were calculated in each case. The geoidal heights on the Bessel ellipsoid were modelled in the area and the coordinate transformation coefficients were derived, and then the accuracy of the transformed coordinates according to fluctuations in geoidal heights were studied.