• The Journal of the Acoustical Society of Korea
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• v.26 no.4
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• pp.173-181
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• 2007

In this paper, we propose a moving target localization algorithm using acoustic spectrograms. A time-versus-frequency spectrogram provide a information of trajectory of the moving target in underwater. For a source at sufficiently long range from a receiver, broadband striation patterns seen in spectrogram represents the mutual interference between modes which reflected by surface and bottom. The slope of the maximum intensity striation is influenced by waveguide invariant parameter ${\beta}$ and distance between target and sensor. When more than two sensors are applied to measure the moving ship-radited noise, the slope and frequency of the maximum intensity striation are depend on distance between target and receiver. We assumed two sensors to fixed point then form a circle of apollonios which set of all points whose distances from two fixed points are in a constant ratio. In case of three sensors are applied, two circle form an intersection point so coordinates of this point can be estimated as a position of target. To evaluates a performance of the proposed localization algorithm, simulation is performed using acoustic propagation program.

• The Korean Journal of Quaternary Research
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• v.31 no.2
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• pp.31-42
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• 2017

Oahu Island is the third largest island of the Hawaiian chain which located in the northern hemisphere close to the center of the Pacific Ocean and is affected by storms and tsunamis in the northern and southern hemispheres. High-wave and high-energy waves are concentrated in the winter and summer, and the Oahu Coast is always in an active erosion environment. These natural effects are likely to become more severe with global warming and sea level rise. In addition, as the anthropogenic factors, there was indiscreet flood of development on the coast until the 1972 coastal management law was enacted. However, the present coastal erosion phenomenon was not serious than thought. The cause can be found in the improvement of the coastal management of the provincial government. The Hawaiian government is no longer applying this method, which was built prior to the enactment of the Coastal Control Act, due to increased erosion and side effects at other sites. So, in Hawaii, it is mainly applied to soft revetment methods such as supplying sand or making artificial sand dunes as an erosion prevention method. In Korea, there are some places where the soft revetment method is applied partially, but it is mainly composed of hard revetment structure.

• Journal of the Korean Society of Earth Science Education
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• v.17 no.2
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• pp.137-152
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• 2024

The purpose of this study is to develop a project-based learning program utilizing Earth science data and to evaluate its effects on students' knowledge-information processing competency and communication and collaboration competency. To achieve this, the ADDIE instructional design model was employed to create the program, which was then implemented with 75 second-year middle school students. The program's effectiveness was assessed using paired sample t-tests on the results of tests measuring knowledge-information processing competency and communication and collaboration competency. Additionally, reflection journals were analyzed to identify students' interest in and difficulties with the program. The study's conclusions are as follows: first, the Earth science data-based project learning program comprises three themes: 'Journey through the Planets of the Solar System,' 'I am a Marine Expert,' and 'Planning a Tidal Flat Experience Program.' Second, following the program's implementation, there was a significant improvement in the overall students' knowledge-information processing competency. Third, the program also led to a significant enhancement in students' communication and collaboration competency. Based on these findings, the study suggests the need for specific and continuous teacher support to provide students with successful experiences through the program, overcoming challenges in program implementation through collaboration with the information subject, and conducting research that microscopically analyzes students' interactions.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.4
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• pp.239-248
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• 2011

This paper evaluated types and characteristics of development projects occurred in coastal area (Public Water) by analyzing an application status of Sea Area Utilization Conference System that effective protect and manage marine environment and ecosystem from various artificial utilization and development enforced in 2008. Also, system improvement for stable settlement and security of efficiency considering exposed problems during system enforcement were diagnosed. The number of Sea Area Utilization Conference (SAUC) performanced during the period of 2009-2010 was 3,705, which consisted of simple SAUC (87.0%), general SAUC (12.8%), and Sea Area Utilization Impact Assessment (SAUIC; 0.2%). The general SAUC was accomplished for Public Water reclamation (43.4%), seawater supply and drainage (17.5%), dredging sediment (5.5%), installation of port facilities (4.6%) and fishing harbor facilities (2.3%), and others (23.4%). Statements of Environmental Impact Assessment (EIA) were reviewed mainly for construction of port facilities (32.9%), followed by construction of industrial complex, development of tourism and leisure complex, road construction, and development of energy facilities. It would be necessary to strengthen effectiveness of the system, advertisement, and capability of conference and review agency, and to enhance confidence of marine EIA continuously, according to the increase of development projects, and diversity and enlargement of development types.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.2
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• pp.41-51
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• 2013

The tidal creek dependent mass transport characteristic in Gyeong-Gi Bay (west coast of Korea) was studied using field measured data and numerical model. Gyeong-Gi Bay consists of 3 main tidal channels and contains a well-developed vast tidal flat. This region is famous for its large tidal difference and strong current. We aim to study the effect of tidal creek in the tidal flat on the mass exchange between the estuary and the ocean. For numerical application, the application of unstructured grid feature is essential, since the tidal creek has complicated shape and form. For this purpose, the FVCOM is applied to the study area and simulation is performed for 2 different cases. In case A, geographic characteristics of the tidal creek is ignored in the numerical grid and in case B, the tidal creek are constructed using unstructured grid. And these 2 cases are compared with the field measured cross-channel mass transport data. The cross-channel mass transport at the Yeomha waterway mouth and Incheon harbor was measured in June, 9~10 (Spring tide) and 17~18 (Neap tide), 2009. CTD casting and ADCP cross-channel transect was conducted 13 times in one tidal cycle. The observation data analysis results showed that mass transport has characteristic of the ebb dominance Line 1 (Yeomha waterway mouth), on the other hand, a flood dominant characteristic is shown in Line 2 (Incheon harbor front). By comparing the numerical model (case A & B) with observation data, we found that the case B results show much better agreement with measurement data than case A. It is showed that the geographic feature of tidal creek should be considered in grid design of numerical model in order to understand the mass transport characteristics over large tidal flat area.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.10 no.4
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• pp.204-212
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• 2005

Recognition has emerged that nutrient inputs from the submarine discharge of fresh, brackish, and marine groundwaters into the coastal ocean are comparable to the inputs via river discharge. The coastal areas of the Korea peninsula and adjacent seas exhibit particular importance in the role of submarine groundwater discharge (SGD), in terms of the magnitude of SGD and associated continental material fluxes. For example, in the southern sea of Korea, SGD transports excess nutrients into the coastal regions and thus appears to influence ecosystem changes such as the outbreak of red tides. Around volcanic island, Jeju, which is composed of high permeability rocks, the amount of SGD is higher by orders of magnitude relative to the eastern coast of North America where extensive SGD studies have been conducted. In particular, nutrient discharge through SGD exerts a significant control on coastal ecosystem changes and results in benthic eutrophication in semi-enclosed Bang-du bay, Jeju. In the entire area of the Yellow Sea, tile submarine discharge of brackish groundwater and associated nutrients are found to rival the river discharges into the Yellow Sea, including those through Yangtze River, Han River, etc. In the eastern coast of the Korea peninsula, SGD is significantly higher during summer than winter due to high hydraulic gradients and due to wide distribution of high permeability sandy zones, faults, and fractures. On the other hand, in the estuarine water, downstream construction of the dam in the Nakdong River, SGD was highest when the river discharge was lowest (but water level of the dam was highest). This suggests that even though there is no visible freshwater discharge into this estuary, the discharge of chemical species is significant through SGD. On the basis of the results obtained from the coastal areas of the Korea peninsula, SGD is considered to be an important pathway of continental contaminants influencing tidal-flat ecosystems, red tides, and coral ecology. Thus, future costal management should pay great attention to the impact of SGD on coastal pollution and eutrophication.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.4
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• pp.37-55
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• 2000

Two-dimensional numerical experiments and field surveys have been conducted to clarify some environmental variations in the flow and sedimentation in the adjacent seas after the construction of a tidal embankment. Velocities of flow and water levels in the bay decreased after the construction of the barrage. When the freshwater was instantly released into the bay, the conditions of flow were unaltered, with the exception of a minor variation in velocities and tidal levels around the sluices at the ebb flow. The computational results showed that freshwater released at the low water reached the outside of the bay and then returned to the inside with the tidal currents at the high water. The front sea regions of the embankment had a variety of sedimentary phases such as a clayish silt, a silty clay and a sandy clayish silt. However, a clayish silt was prevalent in the middle of the bay. On the other hand, the skewness, which reflects the behaviour of sediments, was $\{pm}0.1$ at the front regions of the embankment while it was more than ±0.3 in the middle of the bay. Analytical results of drilling samples acquired from the front of the sluice gates showed that the lower part of the sediments consists of very fine silty or clayish grains. The upper surface layer consisted of shellfish, such as oyster or barnacle with a thickness of 40～50 cm. Therefore, it seemed that the lower part of the sediments would have been one of intertidal zones prior to the embankment construction while the upper shellfish layer would have been debris of shellfish farms formed in the adjacent seas after the construction of the embankment. This shows the difference of sedimentary phases reflected the influence of a tidal embankment construction.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.11 no.4
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• pp.227-231
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• 1978

Effects of suspended silt and clay on the survival of the rearing bivalves, Meretrix lusoria, Cyclina sinensis and Mactra veneriformis were studied. During sixty-five days of experimental cultures in different concentrations of suspended silt and clay and in different time of immersions, mortalities of the bivalves were checked every day, and the rates of shell movement and oxygen consumption were measured. In general, the higher the concentration of silt and clay and the longer the immersion time, the earlier the occurence, and the higher the rate of the mortalities of the experimental bivalves. M. veneriformis was subjected to earlier mortality than the others, and the period of $50\%$ mortality was the shortest of the three species (37 days in 1,000 ppm), and longer was that of C. sinensis(42 days). Mortality of M. lusoria occured latest and $50\%$ mortality was seen at the immersion time of 50-51 days. Particularly, M. lusoria showed no mortality in the sea water with 100 ppm of suspended silt and clay, and even in the concentrations of 500 or 1,000 ppm they were able to survive without mortality only if the immersion time was short (12-18 hours per day). M. veneriformis and C. sinensis were also able to survive without mortality when the immersion time was short (12 hours per day) in low concentration (100 ppm). Shell movements of experimental bivalves varied depending upon species. In the case of M. veneriformis the shell was opened continuously and C. sinensis opened their shells frequently, while M. lusoria maintained their shells closed in any experimental concentrations of sea water with suspended silt and clay. Total metabolic activity of M. veneriformis was found to be highest while that of M. lusoria showed the lowest. Little difference of oxygen consumption in excised gill tissue was shown between the control group and the experimental groups. Consequently, it may be stated that the mortality results from a immersion in sea water with high concentration of suspended silt and clay for long-time although the survival rates of the experimental bivalves depend also upon the species, physiological conditions, concentration of suspended silt and clay and immersion time. The survival percentage of bivalve y in relation to the time (day) of immersion X in sea water of suspended silt and clay was found to be: $$M.\;lusoria\;(1,000\;ppm):\;y=7.7\times10^9\;\chi^{-4.77}\;(500\;ppm):\;y=259\chi^{-0.26}$$ $$C.\;sinensis\;(1,000\;ppm):\;y=-21\chi+936\;(\chi<44),\;y=-0.65\;\chi+35\;(\chi>44)$$ $$(500\;ppm):\;y=4.4\times10^5\;\chi^{-2.27}$$ $$M.\;veneriformis\;(1,000\;ppm):\;y=-18\chi+716\;(\chi<39),\;y=-0.89\chi+39\;(\chi>39)$$

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.2
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• pp.109-118
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• 1985

This experiment was carried out to evaluate the water quality in the lower part of the Nagdong river in Korea. Three hundred and sixty water samples were collected from the 15 stations from December 1981 to November 1982 by tide(see Fig.1). Water temperature, pH, chloride ion, salinity, total coliform, fecal coliform, viable cell count and the composition of coliform were observed to evaluate the water quality. The variations of water temperature was ranged from $2.0^{\circ}C\;to\;29.5^{\circ}C$ and as mean value from $15.8^{\circ}C\;to\;18.9^{\circ}C$. The range of pH was 6.00-8.88 and 7.20-7.96 as mean value. The concentration of chloride ion from St. 1 to 5 was higher as 17.51-771 mg/l in flood tide than 13.12-264.58 mg/l in ebb tide. Specially, water quality at St.1 (Samrangjin) which located about 46 km far from Hadan was also influenced by tide. Salinities of water in flood tide were a litte higher ($11.05{\sim}31.08\%0$) than those of in ebb tide ($7.80{\sim}29.28\%0$). Total coliform MPN's ranged from 3.6/100 m/l to 460,000/100ml. The geometric mean value of the upper area (included St. $1{\sim}3$) was $259{\sim}538/100ml$, that of the middle area (included St. $4{\sim}6$) was $1,097{\sim}39,544/100ml$ for it leveled heavy contamination. Specially, in the ebb tide St. 10 was influenced by St. 6 and 7. In the upper area, the geometric mean value of fecal coliform MPN's was $109{\sim}199/100ml$ but in the area in cluded St. 5, 6 and 7 were heavily contaminated by domestic sewage, waste water from the factories area and bird's excrement. Composition of coliform was $17\%$ Escherichia coli group, $33\%$ Citrobacter freundii group, $28\%$ Enterobacter aerogenes group and $21\%$ others. Plate count of samples was varied from <30 to $3.9{\times}10^4/ml$ during the study period.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.4
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• pp.287-301
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• 2014

In order to understand environment condition and phytoplankton community before and after coastal upwelling, the influences of upwelling events on phytoplankton community were studied at 18 stations located the Southern part of East Sea, Korea from May to August 2013. The surface water masses showed low temperature and high salinity due to upwelling events at coastal stations (A1, B1, C1). Correlation between temperature and nutrients (DIP, r=-0.218, p<0.01; DIN, r=-0.306, p<0.01; silicate, r=-0.274, p<0.01) was significantly negative. This result could be explained that nutrients were supplied to surface water by the upwelling of bottom water. Phytoplankton communities were composed of 186 species. Phytoplankton abundance were relatively high in May (C1, $726{\times}10^3cells\;L^{-1}$) and July (A1, $539{\times}10^3cells\;L^{-1}$). Total chlorophyll a and micro-size fraction ($&gt;20{\mu}m$) increased at coastal stations in July and August, while phytoplankton abundance and total chl. a was much low in June. Dominant species in June was Pseudo-nitzschia spp. of which the cell size was $309{\mu}m^3$. Cell size of Pseudo-nitzschia spp. was smaller than dominant species in other period. Therefore, the increase in total chloro-phyll a and the size of phytoplankton was resulted in the sufficient supply of nutrients. In contrast, these tendencies were not observed at outside stations. These results suggested that coastal upwelling was an important influencing factor to determine the species composition and standing stock of phytoplankton community in the coastal waters of the Southern part of East Sea, Korea.