• Korean Journal of Ecology and Environment
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• v.46 no.4
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• pp.488-498
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• 2013

A three-dimensional hydrodynamic model was applied to the Lake Euiam. The lake has three inflows, of which Gongji Stream has the smallest flow rate and poorest water. The dam-storage volume, watershed area, lake shape and discharge type of the Chuncheon Dam and the Soyang Dam are different. Therefore, it is difficult to analyze the water plume and mixing pattern due to the difference of the two dams regarding the amount of outflow and water temperature. In this study, we analyzed the effects of different characteristics on temperature and conductivity using the model appropriate for the Lake Euiam. We selected an integrated system supporting 3-D time varying modeling (GEMSS) to represent large temporal and spatial variations in hydrodynamics and transport of the Lake Euiam. The model represents the water temperature and hydrodynamics in the lake reasonably well. We examined residence time and spreading patterns of the incoming flows in the lake based on the results of the validated model. The results of the water temperature and conductivity distribution indicated that characteristics of upstream dams greatly influence Lake Euiam. In this study, the three-dimensional time variable water quality model successfully simulated the temporal and spatial variations of the hydrodynamics in the Lake Euiam. The model may be used for efficient water quality management.

• Journal of the Korean Geographical Society
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• v.49 no.6
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• pp.812-832
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• 2014

We analyzed physical and chemical properties of sediments from 20 subtidal points and 9 beach points to define sedimentary environment between summer and winter of Shindu Marine Protected Area. Means of particle size in summer were generally finer than winter's. There was distinctively spatial pattern that particle sizes became increasingly fine as west direction and apart from beach in summer, but this pattern was not shown in winter. Coarse sediments were prevailed in winter. To explain these patterns, we propose possible two causes which are spatially different water depth condition related with seasonal wave climate or fine sediment input from an estuary located in south of this area during summer rainy season. Contents of exchangeable cations of sediment in summer were shown $Na^+$>$Ca^{2+}$>$Mg^{2+}$>$K^+$ in order, but those of winter were shown $Na^+$>$Mg^{2+}{\fallingdotseq}Ca^{2+}$>$K^+$. Contents of $Na^+$, $Mg^{2+}$, and $K^+$ were related with contents of fine sediment and showed high correlation in each other. These relations were not shown between $Ca^{2+}$ and others. Our results show that there are spatio-temporal unique sedimentary environments between subtidal zone, beach, and dune near Shindu Marine Protected Area. Therefore, we should consider these spatio-temporal patterns for environmentally sound management of Shindu coastal system.

• Journal of the Korean Institute of Intelligent Systems
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• v.23 no.4
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• pp.354-359
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• 2013

In this paper, we suggested the method for implementation of unsupervised nonlinear classification using Binary Harmony Search (BHS) algorithm, which is known as a optimization algorithm. Various algorithms have been suggested for classification of feature vectors from the process of machine learning for pattern recognition or EEG signal analysis processing. Supervised learning based support vector machine or fuzzy c-mean (FCM) based on unsupervised learning have been used for classification in the field. However, conventional methods were hard to apply nonlinear dataset classification or required prior information for supervised learning. We solved this problems with proposed classification method using heuristic approach which took the minimal Euclidean distance between vectors, then we assumed them as same class and the others were another class. For the comparison, we used FCM, self-organizing map (SOM) based on artificial neural network (ANN). KEEL machine learning datset was used for simulation. We concluded that proposed method was superior than other algorithms.

• Journal of the Korean Association of Geographic Information Studies
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• v.16 no.4
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• pp.91-105
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• 2013

This study performed an assessment of wave power potential in the Kangwon and Dongnam regions encompassing the East Sea and part of South Sea. Annual electricity production and economic effects of 28 wave energy converters with 750kW capacity were analyzed using significant wave height and peak wave period data(created from the NOAA's NWW3 model) and InVEST software(developed by Stanford University and University of Minnesota). Annual electricity production was estimated to be up to 1,207MWh/year and at least 163MWh/year. The spatial pattern of annual electricity production showed that the sea far from land has higher wave power potential than the sea near coast. The net present value(NPV) of 28 wave energy converters was calculated by considering an operation period of 25 years. When assuming that the electricity produced from wave energy converters is transferred to onshore power plants through underwater cables, the NPV was estimated to be up to 5,883USD(6,600,000KRW) and at least -63,494USD(-71,000,000KRW). In contrast, the NPV increased up to 28,095 USD(31,600,000KRW) when assuming that the electricity is utilized in the Ulleungdo and Dokdo. In addition, it was found that the break-even line of NPV in the East Sea becomes closer towards the land according to the increment of electricity price. The NPV of wave energy converters near the Ulleungdo and Dokdo will be 88,158 USD(99,000,000KRW) if the increment of electricity price is 100KRW.

• Journal of Korea Water Resources Association
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• v.54 no.3
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• pp.167-179
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• 2021

In order to characterize the mixing process of confluence for understanding the impacts of a river on the other river, it has been crucial to analyze the spatial mixing patterns for main streams depending on various inflow conditions of tributaries. However, most conventional studies have mostly relied upon hydraulic or water quality numerical models for understanding mixing pattern analysis of confluences, due to the difficulties to acquire a wide spatial range of in-situ data for characterizing mixing process. In this study, backscatters (or SNR) measured from ADCPs were particularly used to track sediment mixing assuming that it could be a surrogate to estimate the suspended sediment concentration. Raw backscatter data were corrected by considering the beam spreading and absorption by water. Also, an optical Laser diffraction instrument (LISST) was used to verify the method of acoustic backscatter and to collect the particle size distribution of main stream and tributary. In addition, image-based spatial distributions of sediment mixture in the confluence were monitored in various flow conditions by using an unmanned aerial vehicle (UAV), which were compared with the spatial distribution of acoustic backscatter. As results, we found that when acoustic backscatter by ADCPs were well processed, they could be proper indicators to identify the spatial patterns of the three-dimensional mixing process between two rivers. For this study, flow and sediment mixing characteristics were investigated in the confluence between Nakdong and Nam river.

• Journal of the Korean Association of Geographic Information Studies
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• v.14 no.3
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• pp.188-202
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• 2011

Due to emissions of greenhouse gases caused by increased use of fossil fuels, the climate change has been detected and this phenomenon would affect even larger changes in temperature and precipitation of South Korea. Especially, the increase of temperature by climate change can affect the amount and pattern of snowfall. Accordingly, we tried to predict future snowfall and the snowfall pattern changes by using the downscaled GCM (general circulation model) scenarios. Causes of snow varies greatly, but the information provided by GCM are maximum / minimum temperature, rainfall, solar radiation. In this study, the possibility of snow was focused on correlation between minimum temperatures and future precipitation. First, we collected the newest fresh snow depth offered by KMA (Korea meteorological administration), then we estimate the temperature of snow falling conditions. These estimated temperature conditions were distributed spatially and regionally by IDW (Inverse Distance Weight) interpolation. Finally, the distributed temperature conditions (or boundaries) were applied to GCM, and the future snowfall was predicted. The results showed a wide range of variation for each scenario. Our models predict that snowfall will decrease in the study region. This may be caused by global warming. Temperature rise caused by global warming highlights the effectiveness of these mechanisms that concerned with the temporal and spatial changes in snow, and would affect the spring water resources.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.3
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• pp.77-84
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• 2021

In this study, flexural tests of prestressed high strength spun concrete (PHC) piles reinforced with infilled concrete and longitudinal rebars were conducted, where the longitudinal rebar ratio and the presence of sludge formed on the inner surface of PHC pile were set as key test variables. A total of six PHC pile specimens were manufactured, and their flexural behaviors including failure mode, crack pattern, longitudinal strain distribution in a section and end slip between external PHC pile and infilled concrete were measured and discussed in detail. The test results revealed that the flexural stiffness and strength increased as the longitudinal rebar ratio became larger, and that the sludge formed on the inner surface of PHC pile did not show any detrimental effect on the flexural performance. In addition to the experimental approach, this study presents a nonlinear flexural analysis model considering compatibility conditions and strain and stress distributions of the PHC piles and infilled concrete. The rationality of the nonlinear flexural analysis model was verified by comparing it with test results, and it appeared that the proposed model well evaluated the flexural behavior of PHC piles reinforced with infilled concrete and longitudinal rebars with a good accuracy.

• Korean Journal of Remote Sensing
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• v.33 no.6_1
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• pp.947-960
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• 2017

Soil moisture plays an important role to affect the Earth's radiative energy balance and water cycle. In general, satellite observations are useful for estimating the soil moisture content. Passive microwave satellites have an advantage of direct sensitivity on surface soil moisture. However, their coarse spatial resolutions (10-36 km) are not suitable for regional-scale hydrological applications. Meanwhile, in-situ ground observations of point-based soil moisture content have the disadvantage of spatially discontinuous information. This paper presents an experimental soil moisture retrieval using Sentinel-1 SAR (Synthetic Aperture Radar) with 10m spatial resolution for cropland in South Korea. We developed a soil moisture retrieval algorithm based on the technique of linear regression and SVR (support vector regression) using the ground observations at five in-situ sites and Sentinel-1 SAR data from April to October in 2015-2017 period. Our results showed the polarization dependency on the different soil sensitivities at backscattered signals, but no polarization dependence on the accuracies. No particular seasonal characteristics of the soil moisture retrieval imply that soil moisture is generally more affected by hydro-meteorology and land surface characteristics than by phenological factors. At the narrower range of incidence angles, the relationship between the backscattered signal and soil moisture content was more distinct because the decreasing surface interference increased the retrieval accuracies under the condition of evenly distributed soil moisture (during the raining period or on the paddy field). We had an overall error estimate of RMSE (root mean square error) of approximately 6.5%. Our soil moisture retrieval algorithm will be improved if the effects of surface roughness, geomorphology, and soil properties would be considered in the future works.

• Korean Journal of Agricultural and Forest Meteorology
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• v.13 no.4
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• pp.165-170
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• 2011

The ambient concentrations of nitrogen dioxide ($NO_2$) at 65 forest areas were measured every month using passive diffusive samplers from 2002 to 2009 and were compared to those at urban areas in order to investigate the characteristics of temporal and spatial distributions of $NO_2$ from the forest and urban areas. The annually averaged concentrations of $NO_2$ gradually decreased for both areas. The average concentration of $NO_2$ in the forest areas was 8.0 ppb, which was lower than that in the urban areas (i.e., 19.4 ppb) and the ecological standard level of the European Union (i.e., 14.6 ppb). The monthly average of $NO_2$ concentration depicted seasonal variations particularly in the urban areas, showing higher concentration in winter and lower concentration in summer. Strong locality of $NO_2$ concentration distribution illustrates that the locations near the metropolitan areas (e.g., Gyeonggi and Chungnam provinces) had the highest concentration during the measurement period. A significant positive correlation between $NO_x$ emissions and $NO_2$ concentration was observed, suggesting that the magnitude and proximity to sources of atmospheric nitrogen oxides would be important controlling factors.

• Progress in Medical Physics
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• v.12 no.1
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• pp.51-58
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• 2001

Synchrotron radiation (SR) has several advantages over convetional x-rays, including its phase, collimation, and high flux. A synchrotron radiation beamline 5C1 at Pohang Light Source (PLS) was recently built for imaging applications. We have shown that a SR imaging system is useful in imaging microscopic structures. SR with broad-band energy spectrum were adjusted to an object by Si wafers and their energy were approximately ranging from 6 keV to 30 keV. SR were passed through an object and finally transformed into visible lights by CdWO$_4$ scintillator screen. The visible lights which were reflected at an angle of 90 degrees by gold plated mirror were detected by a CCD camera and the image data were acquired using image acquisition system. A high-resolution phantom, capacitor, adult tooth, child tooth, cancerous breast tissue, and mouse lumbar vertebra were imaged with SR imaging system. The Objects were rotated within the field of view of the CCD detector, and their projection image data were obtained at 250 steps over 180 degrees rotation. Image reconstructions were carried out in a PC by using IDLTM(Research systems, Inc., US) program. The spatial resolution of the images acquired by the SR imaging system was measured with a high-resolution chart manufactured for several micrometer resolution. The specimens were also imaged with conventional x-ray radiography system to compare the image quality of radiography obtained with the SR imaging system. The results showed more structural details and high contrast images with SR imaging system than conventional x-ray radiography system. The SR imaging system may have a potential for imaging in biological researches, material applications, and clinical radiography.