• Korean Journal of Remote Sensing
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• v.31 no.4
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• pp.281-291
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• 2015

Sun glint correction methods of hyperspectral data that have been developed so far have not considered the various situations and are often adequate for only certain conditions. Also there is an inaccurate assumption that the signal in NIR wavelength is zero. Therefore, this study attempts to analyze the NIR spectral properties of sun glint effect in coastal waters. For the analysis, CASI-1500 airborne hyperspectral data, bathymetry data and in-situ data obtained at coastal area near Sin-Cheon, Jeju Island, South Korea were used. The spectral characteristics of radiance and reflectance at the five NIR wavelengths (744 nm, 758 nm, 772 nm, 786 nm, and 801 nm) are analyzed by using various statistics, spatial and spectral variation of sun-glinted area under conditions of the bottom types of benthos, barren rocks and sand with similar water depth. Through the quantitative analysis, we found that the relation of water depth or bottom type with sun glint is relatively less which is a similar result with the previous studies. However the sun glint are distributed similarly with the patterns of the direction of wave propagation. It is confirmed that the areas with changed direction of wave propagation were not affected by the sun glint. The spatial and spectral variations of radiance and reflectance are mainly caused by the effect of sun glint and waves. The radiance or reflectance of more sun-glinted areas are increased approximately 1.5 times and the standard deviations are also increased three times compared to the less sun glinted areas. Through this study, the further studies of sun glint correction method in coastal water using the patterns of wave propagation and diffraction will be placed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.2
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• pp.116-127
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• 2002

Most of finite difference numerical models for the simulation of tsunami propagation developed so for are based on the shallow-water equations which are frequently solved by the leap-frog scheme. If the grid size is properly selected, this numerical scheme gives a correct dispersion effect fur constant water depth. However, if the water depth changes, the dispersion effect of tsunamis can not be accurately considered at every grid point in the whole computational domain. In this study we improved the existing two-dimensional dispersion-correction finite difference numerical scheme. The present scheme satisfies the local dispersion relationships of tsunamis propagating over a slowly varying topography while using uniform grid size and time step. To verify the applicability of the improved numerical model, a tsunami due to 1983 East Sea central earthquake is simulated for Korean harbors with the tide gage records such as Sokcho, Mukho, Pohang and Ulsan in the East Sea. Numerical results of the 1983 tsunami are compared with the measured data and the accuracy of the present numerical model is evaluated.

• Korean Journal of Weed Science
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• v.11 no.3
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• pp.159-166
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• 1991

Seven oxyfluorfen formulations were tested for control of 8 weed species and rice injury under four different water depths with various ages of rice seedlings. Among formulations tested, rice injury was slight by formulations of Elvan, Coal Slag, Chitosan and Bentonite B under 0 cm or shallow water depths, and by those of Elvan and Coal Slag under deep water conditions. Weed control was high by Bentonite A and B, and Chitosan, and was low by Elvan. Coal Slag and Sand coated oxyfluorfen, if the target weeds of oxyfluorfen are annual species, further development of Elvan, coal slag, chitosan and Bentonite A would be controlled to increase control efficacy or to decrease rice injury.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.1
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• pp.54-64
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• 1991

To accurately estimate the rate of sediment transport in shallow water bodies, it is necessary to investigate the irregular waves transformation characteristics and nearshore currents produced by random sea waves. Most of studies on numerical models for nearshore currents are based on the theory of monocromatic waves and thus, very few nearshore models take into account the effect of irregularities in the hight, period and directional spreading of incident waves. The numerical simulation model for nearshore currents used in this paper considers the effect of irregularities of incident waves, based on Individual Wave Analysis. The computational results are compared and shown in a reasionable agreement with the experimental data.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.71-80
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• 2001

In order to consider the sediment layer's effect to total acoustic field, we composed a 3 layered fluid model of 2 sediment layers by adding an additional layer to the Pekeris model and found solutions by using Green's function, boundary conditions and Sommerfeld radiation condition. The modes were divided into discrete modes and virtual modes, and confirmed that the characteristic equation to find discrete modes was same as that of Tolstoy and Clay for normal modes. Also, we confirmed that under similar conditions the 3 layered model showed same results as that of Pekeris model. We believe this 3 layered model can be used to study the sediment's effect on the virtual mode of near field.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.334-337
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• 2004

Groundwater chemistry in Namwon area, Korea, was investigated to understand the contribution of geochemical processes on groundwater chemistry. For this study, a total of 279 groundwater samples were collected from 93 wells distributed over the study area. Higher concentrations of major ions are generally encountered in the shallow alluvial wells, suggesting that these chemicals are originated from the surface contamination sources. Mass balance analysis based on reaction stoichiometry reveals that the water chemistry is regulated by three major chemical processes: weathering of silicate/ carbonate minerals, input of C1/SO$_4$ salts, and nitrate generating processes. The results show that mineral weathering is the most dominating factor regulating the groundwater chemistry. However, the groundwaters with the higher salt concentration indicate the larger mineral weathering effect, suggesting that some part of the mineral weathering effect is also associated with the anthropogenic activities such as limes applied to the cultivated lands, carbonates (CaCO$_3$) in the cement materials.

• Journal of Environmental Impact Assessment
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• v.26 no.6
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• pp.553-562
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• 2017

In these days, agricultural reservoirs are considered as a useful resource for recreational purposes, tour and cultural amenity for vicinity communities as well as irrigation water supply. However, many of the agricultural reservoirs are showing a eutrophic or hyper-eutrophic state and high level of organic contamination. In particular, about 44.7% of the aged agricultural reservoirs that constructed before 1945 exceed the water quality criteria for irrigational water use. In addition to external loading, internal nutrient loading from bottom sediment may play an important role in the nutrient budget of the aged reservoirs. The objectives of this study were to characterize variations of thermal structure of a shallow M reservoir (mean depth 1.7 m) and examine the potential of internal nutrient loading by continuous monitoring of vertical water temperature and dissolved oxygen (DO) concentration profiles in 2015 and 2016. The effect of internal loading on the total loading of the reservoir was evaluated by mass balance analysis. Results showed that a weak thermal stratification and a strong DO stratification were developed in the shallow M Reservoir. And, dynamic temporal variation in DO was observed at the bottom of the reservoir. Persistent hypoxic conditions (DO concentrations less than 2 mg/L) were established for 87 days and 98 days in 2015 and 2016, respectively, during the no-rainy summer periods. The DO concentrations intermittently increased during several events of atmospheric temperature drop and rainfall. According to the mass balance analysis, the amount of internal $PO_4-P$ loading from sediment to the overlying water were 37.9% and 39.7% of total loading during no-rainy season in 2015 and 2016, respectively on August when algae growth is enhanced with increasing water temperature. Consequently, supply of DO to the lower layer of the reservoir could be effective countermeasure to reduce nutrient release under the condition of persistent DO depletion in the bottom of the reservoir.

• Ocean Science Journal
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• v.42 no.2
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• pp.103-116
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• 2007

Seasonal changes of tide signal(s), temperature, salinity and current were studied during the years 2004-2005 in the northernmost Gulf of Aqaba, which is under developmental activities, to obtain scientific bases for best management and sustainability. Spectrum analysis revealed permanent signals of tide measurements during all seasons, which represented semidiurnal and diurnal barotropic tides. The other signal periods of 8.13, 6.10-6.32, 4.16 and 1.02-1.05 h were not detected in all seasons, which were related to shallow water compound and overtides of principle solar and lunar constituent and to seiches generated in the Red Sea and the Gulf of Aqaba. Spatial and temporal distribution of temperature, salinity and density showed significant differences between months in the coastal and offshore region and no significant differences among the coastal sites, between the surface and bottom waters and between coastal and offshore waters. Therefore, the temporal and spatial variation of water properties in the northernmost Gulf of Aqaba behave similarly compared to other parts. The coastal current below 12 m depth was weak $(3-6\;cms^{-1})$ and fluctuated from east-northeastward to west-southwestward (parallel to the shoreline), which may be related to the effect of bottom topography and/or current density due to differential cooling between eastern and western parts in the study area, and wind-induced upwelling and downwelling in the eastern and western side, respectively. The prevailing northerly winds and stratification conditions during summer were the main causes of the southward current at 6 and 12 m depths with average speed of 28 and $12cms^{-1}$ respectively.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.463-467
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• 2004

Rosette-type diffusers with four-ports per riser are constructed in relatively shallow water in Korea. However, the trajectorial bending phenomena due to lower-pressure inside the surrounded buoyant jets on the riser was not considered in most models and was not observed without any experimental results. The buoyant jet behavior affected by the bending effect where there have been growing interests need to be verified experimentally and need to be preceded in the analysis of the characteristics of the buoyant jets oil a riser. The hydraulic model experiments have been carried out to investigate the characteristics of the behavior of horizontal buoyant jets discharged from a Rosette-type riser with four ports as well as single port over a certain range of the experimental conditions including initial momentum and initial buoyancy using LIF (Laser Induced Fluorescence) system to obtain concentration fields. The intensity of the fluorescent light in each pixel on the images obtained from LIF system with the tracer of Rhodamine H was converted to the local dye concentration with a set of calibration procedures to account for the non-uniform distribution of light intensity and the attenuation of light energy by water medium. The experimental results shows that the trajectories from Your ports tend to bend more and more to the inner side with the increase of the densimetric Froude number while the buoyant jet from a single port rises up without any bending phenomena. The previous models, VISJET and Seo et al. (2002), do not simulate the trajectories well except the region before the bending section. This study will focus on the analysis of the behavior of the buoyant jets for mainly a Rosette-type riser by conducting hydraulic model experiments using LIF system.

• Journal of Korea Water Resources Association
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• v.38 no.3 s.152
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• pp.179-188
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• 2005

This study on the HwaBuk Multipurpose Dam showed that two- and three- dimensional numerical model experiments, as well as hydraulic model experiments, can be useful analysis tools for engineers. A commercially available RMA2, which solves the shallow water equations, and FLOW-3D, which solves the Reynolds averaged Navier-Stokes equations, were used to simulate the hydraulic model setup. Numerical simulation results on the following were compared with the hydraulic model results: the flow in the reservoir basin and the approaching channel; the discharge in the overflow weir; the water surface profiles in the rollway, chute, and stilling basin; and the pressure distributions in the rollway. It was shown that there is a reasonably good agreement between the numerical model and the hydraulic model for the most of computations. There were, however, some differences between the numerical simulation results and hydraulic model results for the hydraulic jump in the stilling basin because of air entrainment effect.