• 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.

• Water for future
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• v.10 no.2
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• pp.81-90
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• 1977

The research is conducted to study the effect of the soil physical properties in the direct sowing culture on the water requirement, growth, and yield of rice with Early-Tongil at the experimental paddy field of the Sangju agri. and seri. junior college in Keyngbuk province from 6th May to 15th September in 1977. The experimental plots are designed with the four plots which are non-irrigated standard (plowing to 15cm), non-irrigated deep lowed (plowing to 25cm), irrigated standard (plowing to 15cm), and irrigated deep plowing plot (plowing to 25cm) and also each plot is repreated four times by the split plot design. The results obtained are summarized as follows: 1) The soil sample was ML to 10cm depth from ground surface and those from 10cm to 20cm depth and from 20cm to 30cm were CL. Each specific gravity was 2. 6, 2. 6 and 2. 7. 2) The weather during culturing period was the sane as the normal year of mean temperature. The precipitation was little and the distribution of it was disordered comparing to normal year but the heavy sunshine gave good effect on ripening. 3) Percolation loss was increased more at the non-irrigated plot than at the irrigated plot, and that of deep-plowed plot was increased more. 4) Grain yield per 10a. of non-irrigated deep plowed plot was 898kg, it was greated than others but there wa no significance. 5) A significant difference in the number of spikelets per panicle was found between nonirrigated plot and irrigated plot, and the number of spiklelets per panicle at the nonirrigated plot was more than that of the irrigated plot. But there was no significance in the other yield components-number of panicle, fertility abd ripening ratio-at the irrigated plot, ut weight of 100 grains was higher at non-irrigated plot. 6) Yield and growth at the deep plowed plot were higher than those of standard plowed plot.

• Journal of Ecology and Environment
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• v.44 no.4
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• pp.229-240
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• 2020

Background: Genus Quercus is a successful group that has occupied the largest area of forest around the world including South Korea. The acorns are an important food source for both wild animals and humans. Although the reproductive characteristics of this genus are highly variable, it had been rarely studied in South Korea. Therefore, in Seoraksan and Odaesan National Parks (i) we measured the acorn production of Quercus mongolica, an overwhelmingly dominant species in South Korea, for 3 years (2017-2019), (ii) evaluated the spatial-temporal variation of acorn production, and (iii) analyzed the effects of oak- and site-related variables on the acorn production. Results: The annual acorn production of Q. mongolica increased 36 times from 1.2 g m-2 in 2017 to 43.2 g m-2 in 2018, and decreased to 16.7 g m-2 in 2019, resulting in an annual coefficient of variation of 104%. The coefficient of spatial variation was high and reached a maximum of 142%, and the tree size was the greatest influencing factor. That is, with an increase in tree size, acorn production increased significantly (2018 F = 16.3, p < 0.001; 2019 F = 8.2, p < 0.01). Elevation and slope also significantly affected the production in 2019. However, since elevation and tree size showed a positive correlation (r = 0.517, p < 0.001), the increase in acorn production with increasing elevation was possibly due to the effect of tree size. The acorn production of Odaesan for 3 years was 2.2 times greater than that of Seoraksan. This was presumed that there are more distribution of thick oak trees and more favorable site conditions such as deep soil A-layer depth, high organic matter, and slower slopes. Conclusion: As reported for other species of the genus Quercus, the acorn production of Q. mongolica showed large spatial and annual variations. The temporal variability was presumed to be a weather-influenced masting, while the spatial variability was mainly caused by oak tree size.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.3667-3671
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• 2015

Through experiment that does not cause wrinkles in the forming process for the primary purpose for install PCB(Printed circuit board) the thickness variation of the material was investigated. Experimental results was showed that the forming height of the first process had Influence Material thickness variation in the second process, in the first process, the Entrance corner of the die must have round of the product height of 50%, and The height of forming should be as high as the thickness of the material than the original forming. Also as do implement the forming shape in the first process, the thickness of the material is thinned to 85%, Restriking in the second process was that The thickness of the material is thinned to 80%. Therefore, In order to implement a precise shape, Thinking that the material thinning, The die was maintain the shape of the original product, and It was obtain the effect of the compression that the punch is to be longer, as the sum of more than 20% of the material thickness in the depth of the original product.

• The Journal of the Acoustical Society of Korea
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• v.21 no.3
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• pp.213-220
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• 2002

The sound wave in the sea propagates under the effect of water depth, sound velocity structure, sea surface and bottom roughness, and bottom sediment distribution. In particular the sound velocity structure in shallow water varies with time and space, an? the sediment distributes very variedly with place. In order to investigate the seasonal variation of low-frequency sound propagation in the Yellow Sea, the propagation experiments were conducted along the same track in the middle part of the Yellow Sea at various seasons of spring. summer, and autumn. In this paper we consider the measurement results on the propagation loss with the sound velocity structure, and investigate the seasonal variation of the propagation loss. As a result, the propagation losses measured in summer were larger than the losses in spring and autumn. And the propagation losses measured in autumn were smaller than the losses in spring. The seasonal change of the propagation loss increased with the rise of sound frequency and the propagation range.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.4
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• pp.1-12
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• 2007

A method for assessing fatigue vulnerability of steel bridge members considering corrosion and truck traffic variation with time is proposed to evaluate the reduction of fatigue strength in steel bridge members. A fatigue limit state function including corrosion and traffic variation effect is established. The interaction between the average corrosion depth and the fatigue strength reduction factor is applied to the limit state function as the reduction term of strength. Three types of truck traffic change is modeled for representing real traffic change trend. Monte-Carlo simulation method is used for reliability analysis which provides the data to obtain fatigue vulnerability curves. The estimation method proposed was verified by comparing with the results of reference study and applying to the steel bridges in service.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1115-1128
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• 1994

The condition of temperature gradients in asphaltic concrete (Ascon) pavement have been analyzed based on the data collected from 5 major sites in Korea. From this. considering heat transfer by insolation flux and air temperature within pavement slab. temperature variation on the surface of pavement was computed and numerical model using the theory of thermal conductivity was applied to estimate the temperature gradients in depth. To investigate the present condition of asphalt generally used in Korea. the asphalt property tests were applicated on 5 different AP-3 (AC 85~100), and AP-5 (AC 60~70) asphalts classified by penetration index. Uniaxial compression test and indirect tensile test were also carried out for varying temperature conditions to analyze the effect of temperature on the deformation characteristics of Ascon pavement by calculating the variation of static elastic modulus and layer coefficients.

• Smart Structures and Systems
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• v.20 no.2
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• pp.231-246
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• 2017

A recent work by the authors has demonstrated the feasibility of scour evaluation for Kao-Ping-Hsi Cable-Stayed Bridge simply based on ambient vibration measurements. To further attain the goal of scour monitoring, a key challenge comes from the interference of several environmental factors that may also significantly alter the pier frequencies without the change of scour depth. Consequently, this study attempts to investigate the variation in certain modal frequencies of this bridge induced by several environmental factors. Four sets of pier vibration measurements were taken either during the season of plum rains, under regular summer days without rain, or in a period of typhoon. These signals are analyzed with the stochastic subspace identification and empirical mode decomposition techniques. The variations of the identified modal frequencies are then compared with those of the corresponding traffic load, air temperature, and water level. Comparison of the analyzed results elucidates that both the traffic load and the environmental temperature are negatively correlated with the bridge frequencies. However, the traffic load is clearly a more dominant factor to alternate the identified bridge deck frequency than the environmental temperature. The pier modes are also influenced by the passing traffic on the bridge deck, even though with a weaker correlation. In addition, the variation of air temperature follows a similar tendency as that of the passing traffic, but its effect on changing the bridge frequencies is obviously not as significant. As for the effect from the alternation of water level, it is observed that the frequency baselines of the pier modes may positively correlate with the water level during the seasons of plum rains and typhoon.

• The Journal of Engineering Geology
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• v.31 no.2
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• pp.165-178
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• 2021

The influence of Soil-Water Characteristic Curve (SWCC) fitting parameters for an unsaturated natural slope was evaluated through seepage and slope stability analysis as a function of rainfall. Soil samples were collected from the study area in Jirisan National Park and the physical and mechanical characteristics of unsaturated soil layers were measured in laboratory tests. The saturation depth was calculated via seepage analysis by changing fitting parameters α, the parameter related to the Air Entry Value (AEV) and n, the parameter related to the slope of the SWCC in the range of natural conditions. Slope stability analysis using the limit equilibrium method considered the calculated depth of saturation. Results from seepage analysis for various rainfall conditions indicate the saturation depth in the soil layer suddenly increased as the fitting parameter α decreased; the saturation time for the entire soil layer also decreased. Slope stability analysis considering the calculated depth of saturation shows that the slope safety factor rapidly decreased as the fitting parameter α decreased, whereas the variation in slope safety factor was very small when n increased. Hence, fitting parameter α has a large effect on saturation depth during rainfall and therefore on slope stability, whereas slope stability is relatively unaffected by the fitting parameter n.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.3
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• pp.295-301
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• 2008

Bathymetric data collected using a multi-beam echo sounder during marine scientific survey is essential for geologic and oceanographic research works. Accurate measurment of sound velocity profile(SVP) in water-column is important for bathymetric data processing. SVP can vary at different locations during the survey undertaken for wide areas. In addition, an observational error can occur when different equipments(Sound Velocity Profiler, Conductivity Temperature Depth, eXpendable BathyThermograph) are used for measuring SVP at the same water column. In this study, we used an MB-system software to show changes in bathymetry caused by variation of SVP. The analyses showed that the sound velocity(SV) changes due to the depth and thickness of thermocline had more significant effects on the resulting bathymetric data than those of surface mixed layer. The observational errors between SVP measuring instruments did not cause much differneces in the processed bathymetric data. Bathymetric survey line is better to be established to the direction that the change of temperature can be minimize to reduce the variation of SVP during the data acquisition along the survey line.