• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2010.04a
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• pp.429-431
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• 2010

The hybrid geoid model should be determined by fitting the gravimetric geoid to the geometric geoid which were presented the local vertical level. Therefore, it is necessary to find firstly the optimal scheme for improving the accuracy of gravimetric geoid in order to development the high-precision hybrid geoid model. Through finding the optimal scheme for determining the each part of gravimetric geoid, the most accurate gravimetric geoid model in Korea will be developed when the EIGEN-CG03C model to degree 360, 4-band spherical FFT and RTM reduction methods were used for determining the long, middle and short-frequency part of gravimetric geoid respectively. Finally, we developed the hybrid geoid model around Korea by correcting to gravimetric geoid with the correction term. The correction term is modelled using the difference between GPS/Levelling derived geoidal heights and gravimetric geoidal heights. The stochastic model used in the calculation of correction term is the LSC technique based on second-order Markov covariance function. 503 GPS/Levelling data were used to model the correction term. The degree of LSC fitting to the final hybrid geoid model in Korea was evaluated as 0.001m ${\pm}0.054m$.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2010.04a
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• pp.117-119
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• 2010

Geoid is the equi-gravity potential surface. Gravimetric geoidal heights could be determined by the gravity observation values and geometric geoidal heights could be determined by the GPS ellipsoidal heights at benchmark station. In this study, both gravimetric geoidal heights and geometric geoidal heights were determined and compared in mountainous area. For the study, GPS surveying and gravity observation were accomplished at 1st and 2nd order levelling network located in mountainous area in Kyungsanbukdo and Chollanamdo.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.2
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• pp.217-222
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• 2010

The geoid is the level surface that closely approximates mean sea level and usually used for the origin of vertical datum. For the computation of geoid, various sources of gravity measurements are used in South Korea and, as a consequence, the geoid models may show different results. however, a limited analysis has been performed due to a lack of controlled data, namely the GPS/Leveling data. Therefore, in this study, the gravimetric geoids are compared with the geodetic geoid which is obtained through the GPS/Leveling procedures. The gravimetric geoids are categorized into geoid from airborne gravimetry, geoid from the terrestrial gravimetry, NGII geoid(geoids published by National Geographic Information Institute) and NORI geoid(geoi published by National Oceanographic Research Institute), respectively. For the analysis, the geometric geoid is obtained at each unified national control point and the difference between geodetic and gravimetric geoid is computed. Also, the geoid height data is gridded on a regular $10{\times}10-km$ grid so that the FFT method can be applied to analyze the geoid height differences in frequency domain. The results show that no significant differences in standard deviation are observed when the geoids from the airborne and terrestrial gravimetry are compared with the geomertric geoid while relatively large difference are shown when NGII geoid and NORI geoid are compared with geometric geoid. Also, NGII geoid and NORI geoid are analyzed in frequency domain and the deviations occurs in long-wavelength domain.

• 한국지형공간정보학회:학술대회논문집
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• 2005.08a
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• pp.93-99
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• 2005

This paper summarizes a preliminary geoid computation for western Mongolia, utilizing the airborne data collected fall 2004, as part of the NGA-DNSC-ALAGaC-MonMap cooperative airborne gravity project. A gravimetric geoid has been computed using the airborne gravity data, SRTM terrain models and GRACE/EGM global fields. The gravimetric geoid has subsequently been fitted to GPS-leveling data across Western Mongolia, as well as for a special Ulaanbaatar city geoid model.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.1
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• pp.9-15
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• 2018

Precise regional geoid heights on and around Mount Jiri were calculated and were compared to the KNGeoid14 (Korean National Geoid 2014) model. In this study, gravimetric geoid heights were calculated by using RCR (Remove-Compute-Restore) technique and then hybrid geoid heights were calculated by using the LSC (Least Square Collocation) method in the same area. In addition, gravity observation and GNSS(Global Navigation Satellite System) surveying performed in this study were utilized to determine gravimetric geoid heights and to compute hybrid geoid heights, respectively. The results of the study show that the post-fit error (mean and standard deviation) of hybrid geoid heights was evaluated as $0.057{\pm}0.020m$, while the mean and standard deviation of the differences were -0.078 and 0.085 m, respectively for KNGeoid14. Therefore, hybrid geoid heights in this study show more considerable progress than KNGeoid14.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5D
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• pp.741-747
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• 2008

Nowadays, the accuracy of the geoid model has been improved through development of the combination model which was composed of traditional gravimetric geoid and geometric geoid by the GPS/leveling data in USA and Japan. It is a state of the art method in geoid modeling field that what so called hybrid geoid. In this paper, as a basic study to develop Korean hybrid geoid model, we studied gravimetric geoid solutions using three gravity reduction methods (Helmert's condensation method, RTM method and Airy-isostatic method) and evaluated the usefulness of each method in context of precise geoid. The gravimetric geoid model were determined by restoring the gravity anomalies (included TC) and the indirect effects were made from various reduction methods on the EIGEN-CG03C reference field. The results are compared with respect to the geometric geoid undulation determined from 498 GPS/leveling after LSC fitting. The results showed that hybrid geoid with RTM (Residual terrain model) reduction method was most accurate method and the value of the difference compared to geometric geoid was $0.001{\pm}0.053m$.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.12 no.1
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• pp.61-68
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• 1994

Neglecting distant zones in the computation of geoidal heights using Stokes'formula give rise to some truncation errors. The GRS80 Korean Gravimetric geoid Model 1993(KGM93) of the South Korea region was implemented, in this paper, using a combination of satellite-derived GEM-T2 gravity and terrestrial gravity data. A spherical cap size of 30 degree is used on the integration and the truncation error is compensated to the free-air geoid. The results of this study show that the accuracy of the KGM93-C has one meter level.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.13 no.2
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• pp.125-133
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• 1995

The geoidal heights of a country may be computed from astrogedetic, gravimetric or satellite data. In this paper, the geoid models to the Bessel ellipsoid(KGM95-A) have been determined by the astrogedetic method, which is surface fitting techniques using deflections of the vertical and geoid height constraints. Transformation equations and the gravimetric geocentric geoid(KGM93-C) were applied to obtain the geoid height referred to the Tokyo Datum of the Korean geodetic network, the comparison of the astrogedetic results and discussions of the geoid information were added.

• Journal of the Korean Geophysical Society
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• v.9 no.3
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• pp.181-188
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• 2006

The data, methodology, and the resulting accurate gravimetric geoid model for the Korean Peninsula (latitude from 32˚ N to 40˚ N and longitude from 124˚ E to 131˚ E) are presented in this study. The types of used data were a high degree geopotential model (the EGM96 spherical harmonic coefficient set), a set of 12,615 land gravity observations, 1,056,075 shipborne gravity observations, and KMS2002 gravity anomalies from satellite altimetry. The remove-restore technique was successfully applied to combining the above mentioned data sets using up to degree and order 112 of the EGM96 coefficient. The residual geoid was calculated with residual Free-Air anomaly values using the spherical Stokes' formula with a 37-km integration cap radius. The geoid model was referred to WGS84 geodetic system and was tested using a set of GPS/levelling geoid undulations. The absolute accuracy is 0.132 m and some improvement compared to the PNU95 geoid model was found.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.18 no.4
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• pp.359-367
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• 2000

This paper suggests that coefficients models of the Earth's gravitational potential can be used to calculate height anomalies which are then reduced to the geoid undulation to determine more precise geoid undulation. The potential coefficients and modified coefficients of EGM96 and KODEM33 digital elevation model in and around the Korean peninsula were used for this study. The magnitude of height anomaly computed in this study reached 0.025 m and the mean vaule showed -0.015 m. In this study, geometrical geoid undulation was derived from GPS/Leveling data for evaluating the precisely computed geoid undulation. In comparison with geometric and gravimetric geoid undulations, mean value and standard deviation of the differences showed 0.0114 m and 0.2817 m respectively and it showed the improvement of results.