• Journal of the Korean earth science society
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• v.41 no.5
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• pp.478-489
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• 2020

This study presents an analysis of infrasonic signals from two accidental explosions in Gwangyang city, Jeonnam Province, Korea, on December 24, 2019, recorded at 12 infrasound stations located 151-435 km away. Infrasound propagation refracted at an altitude of ~40 km owing to higher stratospheric wind in the NNW direction, resulting in favorable detection at stations in that direction. However, tropospheric phases were observed at stations located in the NE and E directions from the explosion site because of the strong west wind jet formed at ~10 km. The transmission losses on the propagation path were calculated using the effective sound velocity structure and parabolic equation modeling. Based on the losses, the observed signal amplitudes were corrected, and overpressures were estimated at the reference distance. From the overpressures, the source energy was evaluated through the overpressure-explosive charge relationship. The two explosions were found to have energies equivalent to 14 and 65 kg TNT, respectively. At the first explosion, a flying fragment forced by an explosive shock wave was observed in the air. The energy causing the flying fragment was estimated to be equivalent to 49 kg or less of TNT, obtained from the relationship between the fragment motion and overpressure. Our infrasound propagation modeling is available to constrain the source energy for remote explosions. To enhance the confidence in energy estimations, further studies are required to reflect the uncertainty of the atmospheric structure models on the estimations and to verify the relationships by various ground truth explosions.

• Atmosphere
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• v.26 no.3
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• pp.357-372
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• 2016

Northeast Asian regions have recently become the main source of anthropogenic and natural aerosols. Measurement of aerosols on the sea in these regions have been rarely conducted since the experimental campaigns such as ACE-ASIA (Asian Pacific Regional Aerosol Characterization Experiment) in 2001. Research vessel observations of aerosol mass and chemical composition were performed on the Yellow and south sea around the Korean peninsula. The ship measurements showed six representative cases such as aerosol event and non-event cases during the study periods. On non-event cases, the anthropogenic chemical and natural soil composition on the Yellow sea were greater than those on the south sea. On aerosol event cases such as haze, haze with dust, and dust, the measured mass concentrations of anthropogenic chemical and element compositions were clearly changed by the events. In particular, methanesulfonate ($MSA^-$, $CH_3SO_3^-$), a main component of natural oceanic aerosol important for sulfur circulation on Earth, was first observed by the vessel in Korea, and its concentration on the Yellow sea was three times that on the south sea during the study period. Sea salt concentration important to chemical composition on the sea is related to wind speed. Coefficients of determination ($R^2$) between wind speed and sea salt concentration were 0.68 in $PM_{10}$ and 0.82 in $PM_{2.5}$. Maximum wave height was not found to be correlated to the sea salt concentration. When sea-salt comes into contact with pollutants, the total sea-salt mass is reduced, i.e., a loss of $Cl^-$ concentration from NaCl, the main chemical composing sea salt, is estimated by reaction with $HNO_3$(gas) and $H_2SO_4$(gas). The $Cl^-$ concentration loss by $SO_4^{2-}$ and $NO_3^-$ more easily increased for $PM_{10}$ compared to $PM_{2.5}$. The results of this study will be applied to verifying a dust-haze forecasting model. In addition, continued vessel measurements of aerosol data will become important to research for climate change studies in the future.

• Journal of Environmental Science International
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• v.29 no.3
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• pp.257-272
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• 2020

This study investigates the temporal and spatial variations of marine meterological elements (air temperature (Temp), Sea Surface Temperature (SST), and Significant Wave Height (SWH)) in seven coastal waters of South Korea, using hourly data observed at marine meteorological buoys (10 sites), Automatic Weather System on lighthouse (lighthouse AWS) (9 sites), and AWS (20 sites) during 2013-2017. We also compared the characteristics of Temp, SST, and air-sea temperature difference (Temp-SST) between sea fog and non-sea-fog events. In general, annual mean values of Temp and SST in most of the coastal waters were highest (especially in the southern part of Jeju Island) in 2016, due to heat waves, and lowest (especially in the middle of the West Sea) in 2013 or 2014. The SWH did not vary significantly by year. Wind patterns varied according to coastal waters, but their yearly variations for each coastal water were similar. The maximum monthly/seasonal mean values of Temp and SST occurred in summer (especially in August), and the minimum values in winter (January for Temp and February for SST). Monthly/seasonal mean SWH was highest in winter (especially in December) and lowest in summer (June), while the monthly/seasonal variations in wind speed over most of the coastal waters (except for the southern part of Jeju Island) were similar to those of SWH. In addition, sea fog during spring and summer was likely to be in the form of advection fog, possibly because of the high Temp and low SST (especially clear SST cooling in the eastern part of South Sea in summer), while autumn sea fog varied between different coastal waters (either advection fog or steam fog). The SST (and Temp-SST) during sea fog events in all coastal waters was lower (and more variable) than during non-sea-fog events, and was up to -5.7℃ for SST (up to 5.8℃ for Temp-SST).

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.1
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• pp.77-84
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• 2022

A submarine power cable is a transmission cable for carrying electric power below the surface of the water. Recently, submarine cables transfer power from offshore renewable energy schemes to shore, e.g. wind, wave and tidal systems, and these cables are either buried in the seabed or lie on the ocean floor, depending on their location. Since these power cables are used in the extreme environments, they are made to withstand in harsh conditions and temperatures, and strong currents. However, undersea conditions are severe enough to cause all sorts of damage to offshore cables, these conditions result in cable faults that disrupt power transmission. In this paper, we explore the design criteria for such cables and the procedures and challenges of installation, and cable transfer splicing system. The specification of submarine cable designed with 3 circuits of 154kV which is composed of the existing single circuit and new double circuits, and power capacity of 100MVA per cable line. The determination of new submarine cable burial depth and cable arrangement method with both existing and new cables are studied. We have calculated the permission values of cable power capacity for underground route, the values show the over 100MW per cable line.

• Journal of the Korean Geotechnical Society
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• v.26 no.11
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• pp.63-73
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• 2010

Monopiles, used as one foundation option for offshore wind turbines, are usually subjected to great cyclic lateral loads due to wind and wave. In this study, model pile load tests were performed using calibration chamber and three model piles with different pile lengths in order to investigate the behavior of laterally cyclic loaded piles driven into sand. Model test results show that the first loading cycle generates a bigger displacement than the following ones, and the permanent displacement of piles by one loading cycle decreases with increasing the number of cycles. 1-way cyclic loading causes the permanent displacement in the same direction as cyclic loading, whereas 2-way cyclic loading causes the permanent displacement in the reverse direction of initial loading. It is also observed that the permanent displacement of piles due to cyclic lateral loads increases with decreasing relative density of soil and with increasing the magnitude of cyclic loads. However, it is insensitive to the earth pressure ratio of soil and embedded pile length. In addition, based on the model pile load test results, equations for estimation of the permanent lateral displacement and rotation angle of piles due to 1-way cyclic lateral loads are proposed.

• Journal of the Korean Association of Geographic Information Studies
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• v.23 no.3
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• pp.220-235
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• 2020

Heat wave generation in cities is basically affected by global warming, but it is further exacerbated by the impact of artificial heat emission and heat accumulation in the city. In particular, the effects of urban heat waves directly affect the occurrence of tropical nights. Basically, however, the choice of countermeasures against tropical nights is very limited compared to the daytime heat wave response. The purpose of this study was to analyze the characteristics of cold air flow at night as a countermeasure against tropical nights in Daegu Metropolitan City and to suggest its spatial applicability. As a research method, the spatial characteristics (flow velocity, flow rate, flow direction and range) of cold air flow in Daegu were quantitatively analyzed using KLAM_21, a cold air flow analysis program. As a result of the analysis, it was found that cold air generation and flow in the surrounding mountains of Daegu Metropolitan City was very active, but the inflow was limited to the urban area, which has tropical nights. However, it has been shown that the flow of cold air flowing from the surrounding mountains is very active in some urban areas, so it has spatial conditions that are very effective in countering tropical nights. If these spatial conditions are used for the urban planning, it will be very useful to develop countermeasures for tropical nights.

• Journal of the Korean earth science society
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• v.27 no.2
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• pp.221-235
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• 2006

In order to understand the transport mechanism of tidal beach sediments in Deukryang Bay, south coast of Korea, beach profiles, surface sediments, sedimentation rates and hydrodynamic conditions have been investigated. The beach is composed of a steep beach face and gentle low-tide terrace, showing general morphologic characteristics of tide dominated beach. Central beach face of an indented coast becomes flattened in summer, but ridge and runnel system developed in other seasons makes the beach profile rather irregular. These seasonal variations of beach profiles and sedimentation rate indicate that beach sedimentation is mainly controlled by both tide and wave processes. Erosion is prevalent in winter when strong wind wave is dominant, while deposition is dominant in other seasons. However, central beach showed an apparent erosional phase in summer. This is caused by strong waves induced by southerly strong winds occurring ephemerally during the summer. On the other hand, sedimentation rates are -89.2 mm/yr on the central beach and 60.5 mm/yr and 38.2 mm/yr on the sides. This result suggests that sediments are eroded on the central beach and subsequently transported to the both sides. Therefore, the central part of Sumun beach, used as a beach bathing site, will be continuously eroded, if nearby dyke continues to prevent the sediment supply from sources.

• 한국지구물리탐사학회:학술대회논문집
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• 2004.06a
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• pp.3-17
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• 2004

Space-borne Earth observation technique is one of the most cost effective and rapidly advancing Earth science research tools today and the potential field and micro-wave radar applications have been leading the discipline. The traditional optical imaging systems including the well known Landsat, NOAA - AVHRR, SPOT, and IKONOS have steadily improved spatial imaging resolution but increasing cloud covers have the major deterrent. The new Earth observation satellites ENVISAT (launched on March 1 2002, specifically for Earth environment observation), ALOS (planned for launching in 2004 - 2005 period and ALOS stands for Advanced Land Observation Satellite), and RADARSAT-II (planned for launching in 2005) all have synthetic aperture radar (SAR) onboard, which all have partial or fully polarimetric imaging capabilities. These new types of polarimetric imaging radars with repeat orbit interferometric capabilities are opening up completely new possibilities in Earth system science research, in addition to the radar altimeter and scatterometer. The main advantage of a SAR system is the all weather imaging capability without Sun light and the newly developed interferometric capabilities, utilizing the phase information in SAR data further extends the observation capabilities of directional surface covers and neotectonic surface displacements. In addition, if one can utilize the newly available multiple frequency polarimetric information, the new generation of space-borne SAR systems is the future research tool for Earth observation and global environmental change monitoring. The potential field strength decreases as a function of the inverse square of the distance between the source and the observation point and geophysicists have traditionally been reluctant to make the potential field observation from any space-borne platforms. However, there have recently been a number of potential field missions such as ASTRID-2, Orsted, CHAMP, GRACE, GOCE. Of course these satellite sensors are most effective for low spatial resolution applications. For similar objects, AMPERE and NPOESS are being planned by the United States and France. The Earth science disciplines which utilize space-borne platforms most are the astronomy and atmospheric science. However in this talk we will focus our discussion on the solid Earth and physical oceanographic applications. The geodynamic applications actively being investigated from various space-borne platforms geological mapping, earthquake and volcano .elated tectonic deformation, generation of p.ecise digital elevation model (DEM), development of multi-temporal differential cross-track SAR interferometry, sea surface wind measurement, tidal flat geomorphology, sea surface wave dynamics, internal waves and high latitude cryogenics including sea ice problems.

• Korean Journal of Remote Sensing
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• v.33 no.5_3
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• pp.773-786
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• 2017

This study was to analyze data of climate change impacts on social infrastructure using text-mining methodology, and to visualize the spatial information by integrating those with regional data layers. First of all, the study identified that the following social infrastructure; power, oil and resource management, transport and urban, environment, and water supply infrastructures, were affected by five kinds of climate factors (heat wave, cold wave, heavy rain, heavy snow, strong wind). Climate change impacts on social infrastructure were then analyzed and visualized by regions. The analysis resulted that transport and urban infrastructures among all kinds of infrastructure were highly impacted by climate change, and the most severe factors of the climate impacts on social infrastructure were heavy rain and heavy snow. In addition, it found out that social infrastructure located in Seoul and Gangwon-do region were relatively largely affected by climate change. This study has significance that atypical data in media was used to analyze climate change impacts on social infrastructure and the results were translated into spatial information data to analyze and visualize the climate change impacts by regions.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.56-61
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• 2009

Paradigm depending only on fossil fuel for building heat source is rapidly changing. Accelerating the change, as it has been known, is obligation for reducing green house gas coming from use of fossil fuel, i.e. reaction to United Nations Framework Convention on Climate Change. In addition, factors such as high oil price, unstable supply, weapon of petroleum and oil peak, by replacing fossil fuel, contributes to advance of environmental friendly renewable energy which can be continuously reusable. Therefore, current new energy policies, beyond enhancing effectiveness of heat using equipments, are to make best efforts for national competitiveness. Our country supports 11 areas for new renewable energy including sun light, solar heat and wind power. Among those areas, ocean thermal energy specifies tidal power generation using tide of sea, wave and temperature differences, wave power generation and thermal power generation. But heat use of heat source from sea water itself has been excluded as non-utilized energy. In the future, sea water heat source which has not been used so far will be required to be specified as new renewable energy. This research is to survey local heating system in Europe using sea water, central solar heating plants, seasonal thermal energy store and to analyze large scale central solar heating plants in German. Seasonal thermal energy store necessarily need to be equipped with large scale thermal energy store. Currently operating central solar heating system is a effective method which significantly enhances sharing rate of solar heat in a way that stores excessive heat generating in summer and then replenish insufficient heat for winter. Construction cost for this system is primarily dependent on large scale seasonal heat store and this high priced heat store merely plays its role once per year. Since our country is faced with 3 directional sea, active research and development for using sea water heat as cooling and heating heat source is required for seashore villages and building units. This research suggests how to utilize new energy in a way that stores cooling heat of sea water into seasonal thermal energy store when temperature of sea water is its lowest temperature in February based on West Sea and then uses it as cooling heat source when cooling is necessary. Since this method utilizes seasonal thermal energy store from existing central solar heating plant for heating and cooling purpose respectively twice per year maximizing energy efficiency by achieving 2 seasonal thermal energy store, active research and development is necessarily required for the future.