• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.5
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• pp.673-681
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• 2024

The purpose of this study was to estimate the flood flow and the range of inundation in the downstream area of the Aprokgang(Riv.) that occurred in 2024 using satellite images. The study area was the Aprokgang(Riv.) watershed, the longest river in North Korea. Satellite image Sentinel-1A(SAR-C) data was used for flood analysis before and after the flood. As a result of the analysis of the inundation range using satellite images, it was confirmed that there was a change in the water surface before and after the flood. However, the image after the flood was taken six days after the peak discharge of the flood, so there are limitations in extracting the accurate extent of the flooding. As a result of the analysis using satellite precipitation and ground observed rainfall, the rainfall exceeded 500-year rainfall amount, and the peak-flow was simulated as 85,102 m³/s. As a result of analyzing the inundation range by using the contour lines from AW3D30, it was determined that the inundation occurred around the 15 m contour line. In the future, it is need to conduct a study that can extract more scientifically the inundation range through the use of the inundation analysis model.

• Journal of Marine Life Science
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• v.2 no.2
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• pp.62-69
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• 2017

In order to assess the potential environmental factors in the vicinity of a fish cage farm, we investigated the biotic and abiotic factors during a short-term period in summer 2016 in two inner stations of Tongyeong Obi. High water temperature on August 10^th was apparent among the full depth of up to 29℃, which might have been related to the abnormally high temperatures of large amounts of the Changjiang River discharge along the Tongyeong coast. The concentration of nitrate+nitrite, ammonium, phosphate, and silicate ranged from 0.08 to 5.11 μM, 0.08 to 34.62 μM, 0.01 to 1.15 μM, and 1.46 to 31.79 μM, respectively. The nutrients were mainly supplied by precipitation and leaching from the bottom sediments in the fish culture farm area. It was not retained for a long duration because of the phytoplankton consumption and diffusion by water currents. The chlorophyll a concentration varied from 0.49 ㎍ l^-1 to 7.39 ㎍ l^-1. At that time, Chaetoceros debilis, C. pseudocurvisetus, and Pseudo-nitzschia delicatissima were rapidly proliferated and reached the level of 4.74 × 10⁹ cells l^-1. In particular, the lowest dissolved oxygen was recorded at 4.52 ㎍ l^-1 at the bottom layer after bloom. Therefore, even though phytoplankton blooms in summer have frequently occurred in a fish culture farm area, the oxygen-deficient environments were not found in neither the surface nor bottom layers, which implied that the water masses might be well exchanged from the mouth of the northwest and southeast between Obi and Mireuk Island in the study area.

• Journal of the Korean earth science society
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• v.44 no.1
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• pp.13-35
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• 2023

Ocean currents play the most important role in causing and controlling global climate change. The water depth of the Yellow Sea is very shallow compared to the East Sea, and the circulation and currents of seawater are quite complicated owing to the influence of various wind fields, ocean currents, and river discharge with low-salinity seawater. The Yellow Sea Warm Current (YSWC) is one of the most representative currents of the Yellow Sea in winter and is closely related to the weather of the southwest coast of the Korean Peninsula, so it needs to be treated as important in secondary-school textbooks. Based on the 2015 revised national educational curriculum, secondary-school science and earth science textbooks were analyzed for content related to the YSWC. In addition, a questionnaire survey of secondary-school science teachers was conducted to investigate their perceptions of the temporal variability of ocean currents. Most teachers appeared to have the incorrect knowledge that the YSWC moves north all year round to the west coast of the Korean Peninsula and is strong in the summer like a general warm current. The YSWC does not have strong seasonal variability in current strength, unlike the North Korean Cold Current (NKCC), but does not exist all year round and appears only in winter. These errors in teachers' subject knowledge had a background similar to why they had a misconception that the NKCC was strong in winter. Therefore, errors in textbook contents on the YSWC were analyzed and presented. In addition, to develop students' and teachers' data literacy, class materials on the YSWC that can be used in inquiry activities were developed. A graphical user interface (GUI) program that can visualize the sea surface temperature of the Yellow Sea was introduced, and a program displaying the spatial distribution of water temperature and salinity was developed using World Ocean Atlas (WOA) 2018 oceanic in-situ measurements of water temperature and salinity data and ocean numerical model reanalysis field data. This data visualization materials using oceanic data is expected to improve teachers' misunderstandings and serve as an opportunity to cultivate both students and teachers' ocean and data literacy.

• Journal of Korean Society of Forest Science
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• v.53 no.1
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• pp.44-55
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• 1981

Neutral sulfite precooked fir chips were refined in the Asplund Laboratory Defibrator at various temperature ($20^{\circ}C$, $120^{\circ}C$ and $180^{\circ}C$). The effects of refining temperatures on the physical property and morphological structure of the resulting pulps were discussed. Yields of precooked chips (84%, 92% and 100%) and refining temperature affected remarkably the yield of refined pulp, its beatability, sheet strength and morhphological characteristics. Pulp yield and beatability decreased with increasing refining temperature. Fiber surface of unbeaten pulp from precooked chips of 84% yield was to some extent covered by the secondary wall, while that of the pulp form precooked yield of 92% by the compound middle lamella. In the case of uncooked chips, fibers were damaged heavily, and the exposed fiber surface resulted from the equal amount of the secondary wall and the compound middle lamella. In the case of pulps prepared from precooked chips of higher yields (92% and 100%), sheet strength increased linearly as sheet density increased. But at the same sheet density, pulp from lower precooked yield (84%) had better sheet strength after open discharge refining as compared to pressurized refining, because pulp from the former had much amounts of fines fraction of higher water retention value than the latters. And there was observed a little difference in fiber length distribution but nearly similar in its morphology with increasing refining temperature.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.17 no.2
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• pp.87-94
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• 2012

To compare monthly variations of phytoplankton biomass and community composition between in seawater and sediment of the Gomso Bay (tidal flat: approximately 75%), the photosynthetic pigments were analyzed by HPLC every month in 1999 and every two months in 2000. Ambient physical and chemical parameters (temperature, salinity, nutrients, dissolved oxygen, and chemical oxygen demand) were also examined to find the environmental factors controlling structure of phytoplankton community. The temporal and spatial variations of chlorophyll a concentration in seawater were correlated well with the magnitude of freshwater discharge from land. The biomass of microphytobenthos at the surface sediments was lower than that in other regions of the world and 2-3 times lower than phytoplankton biomass integrated in the seawater column. Based on the results of HPLC pigment analysis, fucoxanthin, a marker pigment of diatoms, was the most prominent pigment and highly correlated with chlorophyll a in seawater and sediment of the Gomso Bay. These results suggest that diatoms are the predominant phytoplankton in seawater and sediment of the Gomso Bay. However, the monthly variation of chlorophyll a concentration in seawater at the subtidal zone was not a good correlation with that in sediment of the Gomso Bay. Although pelagic plankton was identified in seawater by microscopic examination, benthic algal species were not found in the seawater. These results suggest that contribution from the suspended microphytobenthos in the tidal flat to the subtidal zone of the Gomso Bay may be low as a food source to the primary consumer in the upper water column of the subtidal zone. Further study needs to elucidate the vertical and horizontal transport magnitude of the suspended microphytobenthos in the tidal flat to the subtidal zone.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.spc
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• pp.30-36
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• 2022

A sensor is needed to continuously and automatically measure the change in HNS concentration in industrial facilities that directly discharge to the sea after water treatment. The basic function of the sensor is to be able to detect ppb levels even at room temperature. Therefore, a method for increasing the sensitivity of the existing sensor is proposed. First, a method for increasing the conductivity of a film using a conductive carbon-based additive in a nanoparticle thin film and a method for increasing ion adsorption on the surface using a catalyst metal were studied.. To improve conductivity, carbon black was selected as an additive in the film using ITO nanoparticles, and the performance change of the sensor according to the content of the additive was observed. As a result, the change in resistance and response time due to the increase in conductivity at a CB content of 5 wt% could be observed, and notably, the lower limit of detection was lowered to about 250 ppb in an experiment with organic solvents. In addition, to increase the degree of ion adsorption in the liquid, an experiment was conducted using a sample in which a surface catalyst layer was formed by sputtering Au. Notably, the response of the sensor increased by more than 20% and the average lower limit of detection was lowered to 61 ppm. This result confirmed that the chemical resistance sensor using metal oxide nanoparticles could detect HNS of several tens of ppb even at room temperature.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.2
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• pp.252-263
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• 1997

Temperature and salinity were observed in Kugum Suro Channel in February, April, August and October 1993. Temperature ranged from $7.0^{\circ}C\;to\;25.0^{\circ}C$ throughout the year and its variation was about $18^{\circ}C$. The maximum temperature difference between surface and bottom was less than $0.75^{\circ}C$ for a year, which meant that the temperature stratification in Kugum Suro Channel was considerably week. Salinity had also a small variation range of less than $0.5\%_{\circ}$. Salinity varied from $34.0\%_{\circ}$ in April to $30.0\%_{\circ}$ in August and its fluctuation patterns were quite similar to the seasonal variations of the precipitation and the duration of sunshine observed at Kohung Weather station. Seasonal variation of sea water density in T-S diagram showed that the water mass in Kugum Suro Channel could be largely affected by regional atmospheric conditions. Temperature increased in ebb tide and decreased in flood tide, but salinity decreased in ebb tide and increased in flood tide for a day. The period of fluctuations in temperature and salinity measured for 25 hours was nearly coincident with the semi-diurnal tide which was predominant in that region. Stratification parameters computed in Kugum Suro Channel areas were less than $4.0J/m^3$ the year round, which indicated that vortical mixing from the bottom boundary caused by tidal current played an important role in deciding the stratification regime in Kugum Suro Channel. In estimating the equation which defines stratification and mixing effects in the observed areas, the tidal mixing term ranged from $4.7J/M^3\;to\;14.1J/m^3$ was greater than any other terms like solar radiation, river discharge and wind mixing.

• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.3
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• pp.131-140
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• 2006

Suspended particulate matter and organic carbon were measured in the Mankyoung river estuary in February, May, July and August 2003. There was a large variance in river discharge between the dry season of February and May and the wet season of July and August. The influx of dissolved organic carbon into the estuary was $8.16{\times}10^2tonC\;month^{-1}$ in the dry season and $5.77{\times}10^3tonC\;month^{-1}$ in the wet season. The influx of particulate organic carbon was $9.37{\times}10^2tonC\;month^{-1}$ and $3.14{\times}10^4tonC\;month^{-1}$ in the dry and wet seasons, respectively. Especially, dissolved organic carbon in the northern part of the site inside the dike was increased in July when torrential rainfall was high. In the research, the distribution of dissolved organic carbon showed conservative behavior with the salinity gradient in the estuary, suggesting that physical mixing between seawater and freshwater dominates the distribution pattern of the dissolved organic carbon in the system. However 60 to 90% of the particulate organic carbon introduced into the estuary was removed from the surface water at the upper estuarine mixing zone of low salinities, showing non-conservative behavior similar with suspended particulate matte r. The completion of the Saemangum Dike is likely to inhibit the exchange of materials between open sea and the Mankyoung estuary. This suggests that the oxidation of organic carbon in the bottom of the estuary may exhaust dissolved oxygen in the confined environment.