• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.3
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• pp.439-447
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• 2019

Some dynamical issues about the Tsushima Warm Current (TWC) are reviewed and checked for the remaining unresolved problems, focusing on the formation of the TWC, seasonal variation of its volume transport and its branching in the East Sea. The TWC is a part of the North Pacific (NP) subtropical gyre driven by the NP global wind system. However, the quantitative amount of volume transport is sensitive to friction, basin geometry, barrier effect and so on. Among many causes suggested by many scientists, subpolar winds are found to be most closely related with the seasonal variation of TWC volume transport. However, more studies relating the latter not only to the subpolar winds but also to those including the subtropical winds seem to be required. The branching of the TWC has been known to be due to the western intensification for the East Korean Warm Current (EKWC) and to the bottom trapping for the Nearshore Branch. Since the former hypothesis is problematic in explaining the seasonal variation of the EKWC, other candidate mechanisms may need to be considered.

• Journal of the Korean Association of Geographic Information Studies
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• v.21 no.3
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• pp.119-126
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• 2018

In this study, In this study, the Datum Level-based hydrography surveying system and the ellipsoid-based system were analyzed to acquire more consistent depth data. For the study, the ellipsoid-based surveying for hydrography was conducted twice for the same track line. And the depth was calculated by correcting rise and fall of water level (water level change by tidal energy and other marine environmental energies) respectively by the traditional water level correction method and ellipsoidally referenced water level correction method. there is able to check that Ellipsoid-based hydrographic surveying data is more improved than Datum Level-based hydrographic surveying data in aspect of level difference phenomenon in the same area (surveying line). This result shows that if the Ellipsoid-based hydrographic surveying is performed, the sea level change (tidal energy and other marine environmental energy) of the survey area in real time could be reflected to more consistent generating bathymetric data.

• Water for future
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• v.27 no.2
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• pp.73-83
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• 1994

The unproper development of the nearshore zone can enhance the diffusion of pollutant in the nearshore zone resulting in unbalanced sediment budget of beach which causes alteration of beach topography. Therefore, it is required to predict the effects of the envirnmental change quantitatively. In this paper, the depth-averaged and time-averaged energy balance equation is selected to acount for the wave transformation such as refraction, shoaling effect, the surf zone energy disipation, wave breaking index and bore, due to wave breaking in the shore region.(Numerical solutions are obtained by a finite difference method, ADI and Upwind. For the calculation of the wave-induced current, the unsteady nonlinear depth-averaged and time-averaged governing equation is derived based on the continuity and momentum equation for imcompressible fluid.) Numerical solutions are obtained by finite difference method considering influences of factors such as lateral mixing coefficient, bed shear stress, wave direction angle, wave steepness, wave period and bottom slope. The model is applied to the computation of wave transformation, wave-induced current and variation of mean water leel on a uniformly sloping beach.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.3
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• pp.203-206
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• 2002

동해 남부해역의 5개 정점에서 유속계 계류에 의한 장기 해류 관측이 한일 공동으로 행해졌다. 1000 m이상의 유속장을 조사하기 위해 각 정점에는 유속계가 두 개씩 부착되어 1∼3년간(1998∼2001년) 계류되었다 유속계 관측 자료는 심층류가 대체로 해저지형을 따라 흐르고 있음을 보여주고 있다. 즉, 울릉분지 남동사면과 야마토해령 서북부해역에서는 주로 북향류가 우세하고, 야마토분지 중앙과 남서쪽 가장자리 해역에서는 남향류가 지배적이며, 야마토분지 남동해역에서는 동향류가 강한 순환 형태를 이루고 있는 것이다 계절별로는 12∼2월의 겨울철에 연중 최대 유속이 보여지며, 일주조의 조석성분과 관성운동의 흔적 외에 3∼5일 주기의 불규칙한 변동은 연중 나타나고 있다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.1
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• pp.7-11
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• 1985

Underwater ambient noise in the depth 5m to 200m layers was measured at 14 point from the 24th of July to 2nd of August, 1984, in the Korean east sea areas. The underwater ambient noise pressure level was depended upon configuration of the sea bottom and sea condition, which was formed type of prevaling noise at a long distance from coast and type of intermittent and regional noise at a short distance from coast.

• The Journal of the Acoustical Society of Korea
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• v.43 no.3
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• pp.293-304
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• 2024

In this paper, efficient and reliable methodologies for conducting sea trials to evaluate the performance of hull-mounted sonar systems is discussed. These systems undergo performance verification during ship construction via sea trials. However, the evaluation procedures often lack detailed consideration of variabilities in detection performance due to seabed topography, seasonal factors. To resolve this issue, temperature and salinity structure data were collected from 1967 to 2022 using ARGO floats and ocean observers data. The paper proposes an efficient and reliable sea trial method incorporating Bellhop modeling. Furthermore, a machine learning model applying a Physics-Informed Neural Networks was developed using the acquired data. This model predicts the sound speed profile at specific points within the sea trial area, reflecting seasonal elements of performance evaluation. In this study, we predicted the seasonal variations in sound speed structure during sea trial operations at a specific location within the trial area. We then proposed a strategy to account for the variability in detection performance caused by seasonal factors, using results from Bellhop modeling.

• Economic and Environmental Geology
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• v.48 no.5
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• pp.379-390
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• 2015

Multibeam backscatter strength is dependent not only on seafloor sediment facies but also on changed incidence angle due to the actual bottom slope. Therefore, the correction for actual bottom slope should be considered before the analysis of backscatter strength. This paper demonstrates the backscatter correction technique for the actual incidence angle and ensonified area. The target area is a part of the eastern Yellow Sea with water depths of 46~55 m. The area is located between the sand ridges and covered by large dunes with various bottom slopes. The dunes usually have the gentle slopes of about $1{\sim}3^{\circ}$, but show some steep slopes of $5{\sim}15^{\circ}$ on the crest. The backscatter strength values on the crest range from -34 to -23 dB, assuming that the bottom is flat. However, this study shows that the backscatter strength range was somewhat reduced (-32~-25 dB) after correction for actual bottom slope. In addition, the backscatter imagery was significantly improved; high and low backscatter strength values on the crest due to the actual bottom slope were normalized. The results demonstrate that the correction technique in this study is an effective tool for processing backscatter strength.

• Journal of the Korean Society of Marine Environment & Safety
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• v.9 no.2
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• pp.73-77
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• 2003

This study focuses on illustrating the effect of a hill on current filed at a channel, and the topographic effects of the hill were studied with various numerical experiments. The model experiments showed that stratification as well as bottom topography had influence on current fields around the hill. Due to stratification effect, Karman vortex formed behind the hill by bottom topography made effects on water movement only in the deep layer. The vortex reduced density field around the hill which resulted in the stratification in the water column, and which also resulted in the movement of isopycnic surface to deep layer both in front and back of the hill. The water in the back of the hill moved upward along ispycnic surface afterward. From these effects, velocity pattern in vertical direction around the hill showed opposite direction, downwrad in front of the hill and upward in the back. However, the upward flows did not seem to have any significant influence on the water conditions in the surface layer, even though strong upward flows were found on both side of the hill.

• Journal of The Geomorphological Association of Korea
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• v.19 no.3
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• pp.143-151
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• 2012

The tsunami disasters and tectonic movements derived from mega-earthquake(M 9.0) which occured in the sea floor of the Pacific side of northeast Japan in March, 2011 were investigated. Landward invasion limit of the tsunami was 4.0km from the present coastline in Sendai coastal plain. It was observed that sandy deposit was dristributed largely in coastward part and muddy deposit was distributed largely in landward part. The ratios of distribution distances of the above two deposits were, respectively, 60~75% and 25~40% of the whole invasion distance of the 2011 tsunami. The ratios of the above distribution distances of tsunami deposits could be used to estimate landward invasion distances of the past maga-tsunamies(e.g. '2,000year B.P. Mega-Tsunami' and 'Jogan Tsunami' etc.) in Sendai coastal plain. The mega-scale tsunami disasters were caused by the low and flat geomorphic condition in the Sendai coastal plain and the increasing effect of tsunami height affected by narrow inlet condition of the so-called Ria's coast in the Sanriku coastal area respectively. Tectonic subsidences caused by the mega-earthquake in march, 2011 were observed in many areas of Ishinomaki, Ogawa, Ogachi and Onagawa coasts in northeast Japan. The displacements of tectonic subsidence were between 0.5 meters and 1.0 meters.

• 한국해양학회지
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• v.1
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• pp.49-55
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• 1971

After the heavy precipitation from April 1969 to September 1970, more than 1.359 10$\^$6/㎥ of fresh water was discharged through diversion channel of the Namgang Dam. The sands and muds in the northern Sachon Bay were moved and swept away by the strong southsard flow which was observed to be speedier than five knots. The shellfish culture facility as well as the oysters and bivalves were buried. In Sachon Bay, a southward surface ebb current of approximately one knot stratifies above the northward flow of approximately 0.5 knot, which seems to be similar to the salt wedge estuary. The stratified current is responsible for the breaking of the gill nets and other fishing gears. The salinity of sea water in Chinju Bay decreased remarkably and the abnormal low salinity water lower than 5 was distributed in Sachon Bay. The low salinity water front was observed in eastern Chinju Bay and the Samchonpo Channel, where the salinity was increased from 4.6 to approximately 30 within half a tidal cycle. These caused the oysters and bivalves die, and drove anchovies and octopus out to the sea and prevented them from approaching the bay. The decrease of salinity causes the decrease of density and osmotic pressure of sea water. Turbid water would prevent the sunlight from penetrate into deep layer.