• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.6
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• pp.457-467
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• 2018

Currently, the regulation and rules for public surveying and the UCPs (Unified Control Points) adapts those of the triangulated traverse surveying. In addition, such regulations do not take account of the unique characteristics of GNSS (Global Navigation Satellite System) surveying, thus there are difficulties in field work and data processing afterwards. A detailed procesure of GNSS processing has not yet been described either, and the verification of accuracy does not follow the generic standards. In order to propose an appropriate procedure for field surveys, we processed a short session (30 minutes) based on the scenarios similar to actual situations. The reference network in Seoul was used to process the same data span for 3 days. The temporal variation during the day was evaluated as well. We analyzed the accuracy of the estimated coordinates depending on the parameterization of tropospheric delay, which was compared with the 24-hr static processing results. Estimating the tropospheric delay is advantageous for the accuracy and stability of the coordinates, resulting in about 5 mm and 10 mm of RMSE (Root Mean Squared Error) for horizontal and vertical components, respectively. Based on the test results, we propose a procedure to estimate the daily solution and then combine them to estimate the final solution by applying the minimum constraints (no-net-translation condition). It is necessary to develop a web-based processing system using a high-end softwares. Additionally, it is also required to standardize the ID of the public control points and the UCPs for the automatic GNSS processing.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.1
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• pp.1-7
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• 2019

In this study, we estimated the tropospheric delay of GNSS (Global Navigation Satellite System) signals during passing through the atmosphere in relation to weather and seasonal factors. For this purpose, we chose four CORS (Continuously Operating Reference Station) stations from inland (CCHJ and PYCH) and on the coast (GEOM and CHJU). A total of 48 days for each station (one set of data for each week) were downloaded from the NGII (National Geographic Information Institute) and processed it using the scientific GNSS software. The average tropospheric delays in winter are less than 2,400 mm, which is about 200 mm less than those in summer. The estimated tropospheric delay shows a similar pattern from all stations except the absolute bias in magnitude, while a large delay was observed for the station located on the coast. In addition, the delay during the day was relatively stable in winter, and the average tropospheric delay was strongly related to the orthometric height. The inland stations have tropospheric delays by the precipitation rather than humidity due to dry weather and difference in temperature. On the contrary, it was primarily caused by the humidity on the sea. The correlation between temperature and water vapor pressure is 0.9 or larger for all stations, and the tropospheric delay showed a high linear relationship with temperature. It is necessary to analyze the GNSS data with higher temporal resolution (e.g. all RINEX data of the year) to improve the stability and reliability of the correlation results.

• Tribology and Lubricants
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• v.35 no.1
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• pp.44-51
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• 2019

The paper presents the rotordynamic performance measurements and model predictions of a fuel cell electric vehicle (FCEV) air compressor supported on gas foil bearings (GFBs). The rotor has an impeller on one end and a thrust runner on the other end. The front (impeller side) and rear (thrust side) gas foil journal bearings (GFJBs) are located between the impeller and thrust runner to support the radial loads, and a pair of gas foil thrust bearings are located on both sides of the thrust runner to support the axial loads. The test GFJBs have a partial arc shim foil installed between the top foil and bump strip layers to enhance hydrodynamic pressure generation. During the rotordynamic performance tests, two sets of orthogonally installed eddy-current displacement sensors measure the rotor radial motions at the rotor impeller and thrust ends. A series of speed-up and coast-down tests to 100k rpm demonstrates the dominant synchronous (1X) rotor responses to imbalance masses without noticeable subsynchronous motions, which indicates a rotordynamically stable rotor-GFB system. Finite element analysis of the rotor determines the rotor free-free (bending) natural modes and frequencies well beyond the maximum rotating frequency. The predicted damped natural frequencies and damping ratios of the rotor-GFB system reveal rotordynamic stability over the speeds of interest. The imbalance response predictions show that the predicted critical speeds and rotor amplitudes strongly agree with the test measurements, thus validating the developed rotordynamic model.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.2
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• pp.324-333
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• 2022

The COVID-19 pandemic reminded us again of the importance of essential workers who perform their roles in maintaining the stability of people's daily lives worldwide. Therefore, the International Maritime Organization and overseas countries designated seafarers as essential workers and proposed relevant measures for their protection to enable them to perform their role. In particular, the International Maritime Organization (IMO) urges related associations and member states to support safe boarding and disembarkation of seafarers. However, Seafarers were restricted from boarding or disembarking, shore leave and hospital treatment in certain countries owing to extreme nationalism. This study compares and analyzes the cases of international organizations and major overseas countries to provide a logical basis for the protection of seafarers who play an essential role in the safety of the global supply chain despite the COVID-19 pandemic. This study identifies the need to protect seafarers and their roles as essential workers in the shipping industry and suggests necessary aspects and institutional improvement measures for improving seafarers' working environment to strengthen the shipping industry's resilience. This study is expected to serve as future basic data for national policies aimed at reflecting the roles of seafarers as essential workers and the need to protect them.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.40 no.4
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• pp.275-292
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• 2022

In order to detect climate changes using satellite imagery, the GCOS (Global Climate Observing System) defines requirements such as spatio-temporal resolution, stability by the time change, and uncertainty. Due to limitation of GK-2A sensor performance, the level-2 products can not satisfy the requirement, especially for spatial resolution. In this paper, we found the optimal pan-sharpening algorithm for GK-2A products. The six pan-sharpening methods included in CS (Component Substitution), MRA (Multi-Resolution Analysis), VO (Variational Optimization), and DL (Deep Learning) were used. In the case of DL, the synthesis property based method was used to generate training dataset. The process of synthesis property is that pan-sharpening model is applied with Pan (Panchromatic) and MS (Multispectral) images with reduced spatial resolution, and fused image is compared with the original MS image. In the synthesis property based method, fused image with desire level for user can be produced only when the geometric characteristics between the PAN with reduced spatial resolution and MS image are similar. However, since the dissimilarity exists, RD (Random Down-sampling) was additionally used as a way to minimize it. Among the pan-sharpening methods, PSGAN was applied with RD (PSGAN_RD). The fused images are qualitatively and quantitatively validated with consistency property and the synthesis property. As validation result, the GSA algorithm performs well in the evaluation index representing spatial characteristics. In the case of spectral characteristics, the PSGAN_RD has the best accuracy with the original MS image. Therefore, in consideration of spatial and spectral characteristics of fused image, we found that PSGAN_RD is suitable for GK-2A products.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.7 no.2
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• pp.401-408
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• 2017

GNSS(Global Navigation Satellite System) is positioning and navigation system using satellites. Accurate positioning is possible in all regions of the world using satellite signals. In Korea, GPS was introduced in the late 1980s. GPS is used in research and work in various fields such as navigation, surveying, and GIS. Since 1995, NGII(National Geographic Information Institute) has installed and operated CORS(Continuously Operating Reference Station) for the practical use of GNSS surveying, RINEX download and VRS(Virtual Reference Station) service was provided for precise positioning. Demand for these services is explosively increasing in the field of surveying. Therefore, there is a need for research to provide good service. In this study, status of national surveying infra structure was researched focused on CORS and its services. As a results, current status of CORS and service were presented. Users of VRS service has increased greatly. In order to provide stable service and advanced surveying, it is necessary to continuously upgrade services such as providing services for various GNSS satellites and securing stability through server redundancy in the data center.

• Economic and Environmental Geology
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• v.56 no.5
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• pp.581-588
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• 2023

This study reports depth-dependent elemental distribution and mineral abundance of the oceanic sediment sample (WP21GPC04) near the Mariana Trench collected during the WP21 expedition in 2021. The elemental distribution determined by μ-XRF shows no significant differences with varying depth, with an average SiO₂ 53.91 wt%, FeO 4.48 wt%, Al₂O₃ 16.56 wt%, MgO 2.56 wt%, CaO 4.79 wt%, Na₂O 3.52 wt%, K₂O 5.48 wt%, similar to the average chemical composition of global subducting sediments (GLOSS). The mineral abundances analyzed using synchrotron XRD, however, vary with depth. While quartz, mica, and plagioclase were identified at all depths, chlorite was found at shallow depths, and zeolite group minerals, phillipsite and heulandite, showed a gradual change in phase fraction with depth. This suggests a change in sedimentation and alteration environments in the region, or the potential for coexistence emerges due to similar sediment stability. Overall, this study will provide a basis for the future investigations on the evolution of sedimentary environment near the Mariana Trench in the western Pacific Ocean and the phase distribution and the behavior of subducting oceanic sediments, which will affect the lithological and geochemical characteristics of the Mariana susduction system.

• The Journal of the Convergence on Culture Technology
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• v.10 no.1
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• pp.159-164
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• 2024

The domestic petroleum market is highly sensitive to changes in international oil prices. So, it is important to identify and respond to those changes. In particular, it is necessary to clearly understand the factors causing the price fluctuations of gasoline, which exhibits high consumption. International gasoline prices are influenced by global factors such as gasoline supplies, geopolitical events, and fluctuations in the U.S. dollar. However, previous studies have only focused on gasoline supplies. In this study, we explore the causal relationship between economic indicators and international gasoline prices using various machine learning-based regression models. First, we collect data on various global economic indicators. Second, we perform data preprocessing. Third, we model using Multiple linear regression, Ridge regression, and Lasso(Least Absolute Shrinkage and Selection Operator) regression. The multiple linear regression model showed the highest accuracy at 96.73% in test sets. As a result, Our Multiple linear regression model showed the highest accuracy at 96.73% in test sets. We will expect that our proposed model will be helpful for domestic economic stability and energy policy decisions.

• Journal of Korea Port Economic Association
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• v.40 no.2
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• pp.157-173
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• 2024

This study analyzed the connectivity of the dry bulk carrier market before and after COVID-19 to examine the impact of COVID-19 on the global shipping market. Using the Quantile Time Frequency Connectedness methodology, we analyzed the dynamic connectedness of major dry bulk indices: the Capesize Index (BCI), Supramax Index (BSI), Panamax Index (BPI), and Handysize Index (BHSI). The results are as follows. First, the total spillover connectedness of the dry bulk carrier market increased during the entire period and in the short term after the outbreak of COVID-19, while it slightly decreased in the long term. Second, the roles among the indices changed according to market conditions, with COVID-19 causing the BPI to change from a net receiver to a net transmitter in the short term and the BSI in the long term, affecting net spillover connectedness. Third, it was observed that long-term connectivity tended to increase more than short-term connectedness under extreme conditions. Fourth, the phenomenon of strengthened connectedness under extreme market conditions was confirmed. These results provide important insights into understanding short-term market shocks and long-term stability trends, demonstrating that the connectedness among dry bulk carrier markets strengthens in global crisis situations such as COVID-19. This provides a basis for assessing the resilience and vulnerability of the shipping market and offers useful information for investors and policymakers in crisis management and investment strategy formulation.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.41 no.1
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• pp.1-8
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• 2004

The INS(Inertial Navigation System) provides high rate position, velocity and attitude data with good short-term stability while the GPS(Global Position System) provides position and velocity data with long-term stability. By integrating the INS with GPS, a navigation system can be achieved to Provide highly accurate navigation Performance. For the best performance, time synchronization of GPS and INS data is very important in GPS/INS integrated system But, it is impossible to synchronize them exactly due to the communication and computation time-delay. In this paper, to reduce the error caused by the measurement time-delay in GPS/INS integrated systems, error compensation methods using separate bias Kalman filter are suggested for both the loosely-coupled and the tightly-coupled GPS/INS integration systems. Linearized error models for the position and velocity matching GPS/INS integrated systems are Int derived by linearizing with respect to its time-delay and augmenting the delay-state into the conventional state equations for each case. And then separate bias Kalman Inter is introduced to estimate the time-delay during only initial navigation stage. The simulation results show that the present method is effective enough resulting in considerably less position error.