• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
• /
• 2010.04a
• /
• pp.35-37
• /
• 2010

To construct precision geoid model, the gravity data having equal distribution and quality is necessary. In previous study, however, the geoid model has low precision since the biased distributed gravity data and some unverified data has been used and the gap between land and ocean exists. Now, the airborne and land gravity data was collected by various survey and the ship-borne gravity data and altimeter data has been achieved. Therefore, the precision geoid model development would be possible. And the GPS/Leveling data obtained by NGII could be used for construction of hybrid geoid in Korea. In this study, the procedure of geoid construction based on airborne, land, ship-borne and altimeter data using Remove-Restore technique will be explained. And the verification of gravimetric geoid and hybrid geoid would be introduced.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.15 no.9
• /
• pp.1833-1839
• /
• 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.

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

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

• Economic and Environmental Geology
• /
• v.35 no.5
• /
• pp.455-463
• /
• 2002

There have been few geophysical studies on the crustal structure of the continent-ocean zone around the middle eastern part of Korean peninsula, because of the lack of database in both land and ocean. The area for the study on the internal crustal structure using gravity data is bounded by the latitude of 37$^{\circ}$-38"N and longitude of 128$^{\circ}$-132$^{\circ}$E. WCA correction is applied to shipborne gravity data to integrate with gravity anomalies obtained on land. The high frequency components of the shipborne gravity data which are considered as the noise on survey track are effectively removed by means of correlating with satellite gravity data. The corrected shipborne free-air gravity anomaly is integrated with the Bouguer gravity anomaly on land under the same condition. The integrated gravity anomaly is divided into four areas for power spectrum analysis. The depths of Moho discontinuity increases gradually from inland to Ulleung basin. As the result of modeling based on power spectrum analysis, Moho discontinuity depth is about 33-35 km in the continental zone of Korea and 18-28 km at the continental margin. Such structural character is well elucidated in changing gravity data around Ulleung basin. The depths of Moho discontinuity in the southern ocean of Ulleung-island is 16--17 km, which is much lower than in the land. The result of crustal structure modeling in this study is similar to that computed by prior seismic exploration around this area.

• Journal of Korea Water Resources Association
• /
• v.45 no.8
• /
• pp.805-814
• /
• 2012

Most hydrologic data are obtained by ground observations. New observation methods are needed for some regions to overcome difficulties in accessibility and durability of long-term observation. In 2002, NASA launched twin satellites named GRACE which were designed to measure the gravitational field of the earth. Using the GRACE monthly gravity level-2 data, we calculated terrestrial water storage change (TWSC) of the Korean peninsula in various spatial smoothing radii (0 km, 300 km, 500 km). For the validation of GRACE-based TWSC, we compared it with land-based TWSC which was obtained using the ground observation data: precipitation and evaporation from WAMIS, and runoff from GLDAS. According to the mean square-error test, GRACE-based TWSC best fits the land-based one at 500 km smoothing radius. The variation of the terrestrial water storage in the Korean peninsula turned out to be 0.986 cm/month, which means that appropriate measures should be prepared for sustainable water resources management.

• Spatial Information Research
• /
• v.17 no.3
• /
• pp.397-404
• /
• 2009

To solve the problems of distribution and quality on land gravity data, airborne gravity survey was performed in 2008 obtaining the airborne gravity data with accuracy of 1.56mGal. Since airborne gravity data is the obtained at the flight height, it is necessary to convert the airborne gravity data to the surface to combine various gravity data and compute precision geoid. In addition, Stokes' integral radius, Stokes' kernel and the radius of terrain effect computation should be optimally determined to calculate precision geoid. In this study, we made an effort to decide the optimal parameters based on the distribution and the characteristic of gravity data. Then, two geoid models were calculated using the selected parameters and the difference of geoid was calculated with mean of -16.95cm and the standard deviation of ${\pm}8.50cm$. We consider that this difference is due to the distribution and errors on the gravity data. For future work, the study on the effect of geoid with newly obtained land gravity data ship-borne gravity data and GPS/Leveling data should be conducted. Furthermore, the study on the downward continuation and terran effect calculation should be studied in detail for better precision geoid construction.

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

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

• Journal of Korean Society of Transportation
• /
• v.27 no.6
• /
• pp.19-28
• /
• 2009

In case of land development projects constructed, to solve induced transportation volume needs analysis of traffic demand. Trip-generation of land development projects is exactly predicted by using traffic instigating-basic-unit in each facility of land developments. But in case of a phase of trip-distribution, because a range of destinations is very enormous and it needs enormous data to reflect all of its characters, whenever trip-distribution is predicted, the method which assumes the rate of trip-distribution is same both before completion of land development projects and after is often used. But because there is no exact criterion, the method suggested above is also affected by subjective opinion. Accordingly, this study look over using trip-distribution of specific areas's DB and suggests a size of zone to predict a distribution of land development projects exactly. Also production - constrained gravity model which uses the gap between a distribution of suggested ranges and induced land development project is suggested for more exact prediction of trip-distribution. Besides accuracy of prediction is scrutinized by using Mean Squared Error.