• 한국지구물리탐사학회:학술대회논문집
• /
• 2007.06a
• /
• pp.42-47
• /
• 2007

We have studied feasibility of the geostatistical approach to enhance the result of analysis of the sparsely obtained MT(Magnetotelluric) data by combining with gravity data. We have attempted to use geostatistics for integrating the MT data along with gravity data. To evaluate the feasibility of this approach, we have studied about interrelation between geological boundary and density distribution, and corrected density distribution for conversion to more sensitive to geological boundary by minimization of difference between z-directional variogram values of resistivity distribution obtained MT inversion and density distributions. Then, this method has been tested on model and field data. In model test, the results obtained were good agreement with real model. And in a real field data, the result of analysis demonstrate convincingly that our geostatistical approach is effective.

• Journal of the Korean earth science society
• /
• v.42 no.4
• /
• pp.445-458
• /
• 2021

Gravity Recovery and Climate Experiment (GRACE) gravimeter satellites observed the Earth gravity field with unprecedented accuracy since 2002. After the termination of GRACE mission, GRACE Follow-on (GFO) satellites successively observe global gravity field, but there is missing period between GRACE and GFO about one year. Many previous studies estimated terrestrial water storage (TWS) changes using hydrological models, vertical displacements from global navigation satellite system observations, altimetry, and satellite laser ranging for a continuity of GRACE and GFO data. Recently, in order to predict TWS changes, various machine learning methods are developed such as artificial neural network and multi-linear regression. Previous studies used hydrological and climate data simultaneously as input data of the learning process. Further, they excluded linear trends in input data and GRACE/GFO data because the trend components obtained from GRACE/GFO data were assumed to be the same for other periods. However, hydrological models include high uncertainties, and observational period of GRACE/GFO is not long enough to estimate reliable TWS trends. In this study, we used convolutional neural networks (CNN) method incorporating only climate data set (temperature, evaporation, and precipitation) to predict TWS variations in the missing period of GRACE/GFO. We also make CNN model learn the linear trend of GRACE/GFO data. In most river basins considered in this study, our CNN model successfully predicts seasonal and long-term variations of TWS change.

• 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 the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.8
• /
• pp.58-68
• /
• 2003

Accurate estimation of the Earth gravity field plays an important role in understanding the Earth geodynamic activities. After brief discussion on the objective of the gravity estimation, dedicated satellite missions for this purpose are described. Recently launched NASA/DLR Gravity Recovery and Climate Experiment (GRACE) mission, which consists of two co-orbiting low altitude satellites, is described. For the performance analysis, full numerical simulation was performed. The simulation procedure and its key instrument modelings are described. From the simulation results, a significant improvement on the Earth gravity field accuracy is expected.

• Journal of Biosystems Engineering
• /
• v.41 no.3
• /
• pp.170-176
• /
• 2016

Purpose: This study aimed to improve the method for determining the position of the center of gravity for agricultural tractors. Methods: The proposed method uses trigonometric functions and coordinate transformation. Data were measured according to the ISO 789-6 test procedures for the center of gravity of agricultural tractors. The height calculated using the proposed method was compared with that determined from an AutoCAD drawing. To find the center of gravity of the tractor, the algorithm for finding the intersection of the two lines was used. Results: The vertical height from the ground to the center of gravity is 682.06 mm. The vertical coordinates obtained from the calculation and the drawing were the same. Conclusions: The developed method uses trigonometric and polar coordinate transformation. The method was compared and verified with the AutoCAD drawing results. The results indicate that users can apply this developed method instead of the plotting method which is an inconvenient and time-consuming. Further, users can program Microsoft Excel to easily determine the vertical coordinate. In addition, researchers will propose this method to the ISO as a standard method for determining the center of gravity in accordance with ISO 789-6.

• Journal of the Korean earth science society
• /
• v.23 no.1
• /
• pp.15-29
• /
• 2002

Bayesian inversion for gravity and resistivity data was performed to investigate the cavity structure appearing as a lava tunnel in Cheju Island, Korea. Dipole-dipole DC resistivity data were proposed for a prior information of gravity data and we applied the geostatistical techniques such as kriging and simulation algorithms to provide a prior model information and covariance matrix in data domain. The inverted resistivity section gave the indicator variogram modeling for each threshold and it provided spatial uncertainty to give a prior PDF by sequential indicator simulations. We also presented a more objective way to make data covariance matrix that reflects the state of the achieved field data by geostatistical technique, cross-validation. Then Gaussian approximation was adopted for the inference of characteristics of the marginal distributions of model parameters and Broyden update for simple calculation of sensitivity matrix and SVD was applied. Generally cavity investigation by geophysical exploration is difficult and success is hard to be achieved. However, this exotic multiple interpretations showed remarkable improvement and stability for interpretation when compared to data-fit alone results, and suggested the possibility of diverse application for Bayesian inversion in geophysical inverse problem.

• Economic and Environmental Geology
• /
• v.31 no.6
• /
• pp.535-545
• /
• 1998

Various geophysical methods have been applied to the survey of the lava tunnel of Manjanggul in Cheju Island to study the effectiveness of each method in investigating underground tunnels. The surveys employing gravity, magnetic, electrical, AMT and VLF methods were carried out along seven profiles across the Manjanggul; especially, all the five methods were used on one representative profile. Several aspects of different methods pertinent to their use in investigation of underground tunnels have been noted. The electrical method employing the dipole-dipole array appeared to be the most effective one among five methods. Therefore, we have tested the electrical method more carefully by using various electrode spacings, and obtained successful resistivity sections showing the existence of lava tunnels. The gravity method provided relatively successful responses associated with the tunnel although the gravity readings were contaminated by wind blowing during the survey. The gravity data were also useful for the quantitative modeling study. The magnetic data were also successful in delineating the tunnel qualitatively. The AMT data were not successful because the used frequency band was not appropriate in detecting very shallow target. The VLF data were severely influenced by the neighboring noise sources such as power lines and were not successful in detecting the tunnel responses. The comprehensive result of electrical, gravity and magnetic surveys suggests that undiscovered lava tunnels may exist adjacent to the Manjanggul.

• Economic and Environmental Geology
• /
• v.32 no.3
• /
• pp.281-291
• /
• 1999

This study presents the gravity data with GPS survrying and the geophysical profiles at the Choogaryeong Rift Valley. And in determing geoid by GPS measurement, survey control points (SCP) whoch built by the Republic of Korean Army are used. Seventy nine SCP and the two triangulation stations are reviewd by GPS. Digital terain model is under for terrain analysis. The analyses of the gravity surveying with GPS are as follows. The low values of the negative Bouguer anomalies represent the high elevation terrain. The Bouguer anomalies show the decrrasing trend toward the eastern part of the study area. Characteristics of free-air anomalies are related with terrain elevation. The regional gravity anomalies decreas toward the eastern part of the study area. The trends of variations are associated with the thermotectonic and geologic structure beneath the Choogaryeong Rift Valley. The most parts of the study area represent negative residual gravity anomalies due to the low dencity of sedimentary cover in the Rift Valley. There are three valleys and four mountains in the direction of NE-SW or NNE-SSW which are structured by the geological features.

• 한국데이터정보과학회:학술대회논문집
• /
• 2003.05a
• /
• pp.77-88
• /
• 2003

Cluster analysis has been widely used in many applications, such that data analysis, pattern recognition, image processing, etc. But clustering requires many hours to get clusters that we want, because it is more primitive, explorative and we make many data an object of cluster analysis. In this paper we propose a new clustering method, 'Clustering algorithm using a center of gravity for grid-based sample'. It is more fast than any traditional clustering method and maintains accuracy. It reduces running time by using grid-based sample and keeps accuracy by using representative point, a center of gravity.

• Asian Journal of Business Environment
• /
• v.13 no.1
• /
• pp.31-41
• /
• 2023

Purpose: This study purposes to analyze the determinants of the volume of Indonesian tuna exports. Research design, data and methodology: The framework was developed from the gravity model for trade, which was expanded with additional variables of competitiveness, exchange rate, and industrial share of the destination country. The data sources used in this study are UN Comtrade and the World Bank. The data used is yearly data from 12 countries in 2001-2019. The scope of the study is limited to exports to the twelve main export destinations. Panel data regression analysis is used to determine the factors that affect the volume of Indonesian tuna exports. Results: The results show that according to the theory, Indonesia's GDP has a positive effect and economic distance has a negative effect on the volume of the exports. Meanwhile, the GDPs of the destination countries are not proven to have a positive effect. However, the higher the industrial share in the country, the higher the export volume tends to be. Conclusions: The conclusion obtained from this study is that Indonesia's GDP, economic distance, real exchange rate, industrial GDP share of the destination country, and the RCA index affect the volume of Indonesian tuna exports.