• 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.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.1
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• pp.81-89
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• 2011

The previous land gravity data in Korea showed locally biased irregular distribution. Especially, this problem was more serious in the mountainous area where the data density was significantly low. The same problem appeared in GPS/Levelling data thus the precision of the geoid could not be improved. From 2008, new gravity and GPS/Levelling data has been collected by the unified control point and survey on the benchmark project which were funded by the national geographic information institute. The newly obtained data has much better distribution and precision so that it could be used for update precision of geoid model. In this study, the new precision geoid has been calculated based old and new gravity data and this model showed 5.29cm of precision compared to 927 points of GPS/Levelling data. And the degree of fit and precision of hybrid geoid has been calculated 2.99cm and 3.67cm. The new gravimetric geoid has been updated about 27% over whole country. And it showed 42% of precision update due to collection of new gravity data on the Kangwon/Kyeongsang area which showed quite low distribution. In 2010, about 4,000 points of gravity and 300 points of GPS/Levelling data has been obtained by unified control and survey on benchmark project. We expect that new data will contribute to updating geoid precision and veri tying precision more objectively.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.3
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• pp.319-325
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• 2011

It has been used not orthometric height but normal orthometric height for the official height in Korean benchmark because it has been used not observed gravity but normal gravity for the computation of orthometric correction. The purpose of this study is to propose height renewal method of Korean benchmark. For this purpose, we observed gravity by CG5 digital gravimeter in both the first benchmark line between Sokcho and Gangneung area and the second benchmark line between Soksa and Inje area. We calculated relative gravity value and orthometric correction in all benchmarks. So, the maximum orthometric correction shows -0.349mm in the first benchmark line, and the maximum orthometric correction shows -44.060mm in the second benchmark line. In conclusion, we can confirm that the orthometric correction based on observed gravity is necessary for more accurate official height computation in the Korean benchmark.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.1
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• pp.99-106
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• 2010

A vertical datum requires an origin, which is a point on the Earth's surface where the height of the point is a defined value(26.6871m). From this origin point, heights (height differences) can be measured to any other point using standard leveling and gravity measurement procedures. However, the leveling network over the Korea bas been established by using the normal gravity instead of the actual gravity values, and the heights for the points are published by National Geographic Information Institute (NGII). This may cause height for especially in the area where high-relief mountains are dominant. Therefore, the height errors caused by using normal gravity instead of actual gravity values are analyzed in this study. Then, the differences between the orthometric heights and the published heights, i.e., normal orthometric height are analyzed.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.25 no.4
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• pp.299-307
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• 2007

This study is about the calculation of practical orthometric height for permanent GPS station. We presented the method to determine the orthometric height precisely by combining leveling data, GPS data and gravimetry data, and determined the orthometric heights of thirty GPS stations. To test the result we developed the expected error model fur the determined orthometric heights regarding the accuracy of Korean national benchmarks and the precision of surveying methods used at this project. The reliability of the results was presented by comparing it with expected error model statistically.

• Journal of the Korean Association of Geographic Information Studies
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• v.24 no.2
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• pp.78-90
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• 2021

In order to construct a precision geoid, it has been diversified into land, sea, aviation, and satellite gravity measurement methods, and measurement technology has developed, making it possible to secure high-resolution, high-precision gravity data. The construction of precision geoids can be fast and conveniently decided through GNSS surveys without separate leveling, and since 2014, the National Geographic Information Institute has been developing a hybrid geoid model to improve the accuracy of height surveying based on GNSS. In this study, the results of the GNSS height measurement were compared and analyzed choosing existing public reference points to verify the GNSS height measurement of public surveys. Experiments are conducted with GNSS height measurements and analyzed precision for public reference points on coastal, border, and mountainous terrain presented as low-precision areas or expected-to-be low-precision in research reports. To verify the GNSS height measurement, the GNSS ellipsoid height of the surrounding integrated datum to be used as a base point for the GNSS height measurement at the public datum. Based on the checked integrated datum, the GNSS ellipsoid of the public datum was calculated, and the elevation was calculated using the KNGeoid18 model and compared with the results of the direct level measurement elevation. The analysis showed that the results of GNSS height measurement at public reference points in the coastal, border, and mountainous areas were satisfied with the accuracy of public level measurement in grades 3 and 4. Through this study, GNSS level measurement can be used more efficiently than existing direct level measurements depending on the height accuracy required by users, and KNGeoids 18 can also be used in various fields such as autonomous vehicles and unmanned aerial vehicles.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.22 no.1
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• pp.45-52
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• 2004

It can be classified in various methods to get the geoidal heights. It can be achieved geometric geoidal heights if we do GPS surveying in leveling point. The aims of this paper are calculation of geometric geoidal heights using GPS/leveling data in study area and evaluation of the global and local geoid models in and around Korean peninsula. For this study, study area was selected in the leveling line from Kunsan to Chonju city and GPS surveying was accomplished in the leveling line. And, also spherical harmonic analysis was made on the three global geopotential models, OSU91A, EGM96, EGM96m under same condition. Then the differences were calculated between geometric geoidal heights and geoidal heights of 3 geopotential models, KOGD2002 which was Korean gravimetric geoid model. The results shows that EGM96m is the best model because the differences between geoidal heights of E6M96m and geometric geoidal heights of GPS/Leveling data appear the smallest value among them.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.23 no.4
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• pp.353-358
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• 2005

The purpose of this paper is to evaluate a new geopotential model, EIGEN-CG01C which had been developed from CHAMP and GRACE mission observations and surface gravity data. The accuracy analysis was conducted by comparing the geoidal heights computed from two types of geopotential models (i.e., EIGEN-CG01C and EGM96) with spirit leveled GPS bench mark. To this end, three hundred twenty GPS leveled bench marks are used as bases for the numerical investigation. From the analysis, it was possible to conclude that EIGEN-CG01C was more suitable to upgrade the KGEOID 98 since the results that the EGM96 was slightly biased.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2008.10a
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• pp.203-204
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• 2008

EGM96 지구중력장모델을 개선시킨 EGM2008 지구중력장모델이 미국 NGA에 의해 발표됨에 따라, 본 연구에서는 EGM2008지구중력장모델을 한반도 지역을 대상으로 최대차수 360으로 해석하여 기존의 지구중력장모델인 EGM96(360차수) 및 EIGEN-GL04C(360차수)와 비교하였다. 또한 EGM2008은 기존의 구면조화분석한계인 360차수를 뛰어넘고 있으므로 격자 간격 $30'{\times}30'$ 및 $15'{\times}15'$, 그리고 $10'{\times}10'$로 각각 해석하여 지오이드고를 계산하고 정확도를 평가하였다. 정확도 평가는 우리나라의 수준점에서 GPS측량을 실시한 464점의 GPS/leveling 데이터를 활용하였다. 평가결과 EGM2008(360차수)은 $-0.100{\pm}0.183m$를 나타내 EGM96(360차수)결과인 $0.156{\pm}0.238m$에 비해 상당한 정확도의 개선을 가져왔으며, 2190차수의 고차항으로 해석한 결과 $-0.069{\pm}0.140m$ 더욱 정확한 결과를 얻을 수 있음을 확인하였다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.30 no.5
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• pp.493-500
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• 2012

The previous geoid model developed in early 2000s shows 14cm level of precision due to the problems on distribution, and quality of the land gravity and GPS/Leveling data. From 2007, the new land and airborne gravity data as well as GPS/Leveling data having high quality and regular distribution has been obtained. In 2011, a new gravimetric geoid model has been constructed with precision of 5.29cm which was improved about 27% comparing to the previous model. However, much more land gravity data has been collected at the control point, bench marks and triangulation points since 2010. Also, GPS/Leveling data having 10km spacing over whole country has been obtained through the project which is for the construction of new control points. In this study, new gravimetric geoid has been calculated based on the all available gravity data up to present. The geoid height shows the range from 18.05m to 32.70m over whole country and its precision is 5.76cm. The degree of fit and precision of hybrid geoid model are 3.60cm and 4.06cm, respectively. At the end, 3.35cm of the relative precision in 15km baseline has been calculated to confirm its practical usage. Especially, it has been founded that regional bias occurred at the Kangwon and coastal area due to problems on the leveling data. Also, some inland points show inconsistent large difference which needs to be verified by analyzing the unified control points results.