• Korean Journal of Optics and Photonics
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• v.18 no.1
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• pp.66-73
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• 2007

The various output characteristics of a pulsed Ti:sapphire laser oscillator with a plane-parallel resonator, pumped longitudinally by the second harmonic wave of a Nd:YAG laser, and the output of a Ti:sapphire laser amplifier operated along the single path of the oscillator beam were investigated and analyzed. In the case of the oscillator, we measured the spectrum, the pulse buildup time, the temporal duration time of the pulse, and the output energy according to the variation of the pumping energy, resonator length, and the reflectance of the output coupler. And, in the case of the amplifier, we investigated and analyzed the output energy of the amplifier as a function of the time difference between the two pump beams of the oscillator and the amplifier, the pumping energy of the oscillator, and the pumping energy of the amplifier When pump energies of both the oscillator and the amplifier were 18 mJ/pulse, we could find that the output energy of the amplifier increased linearly and gradually up to the time difference of 35 ns. Finally, we determined that the slope efficiencies of the oscillator and the amplifier were 23.5 % and 11.6 %, respectively.

• Journal of Korea Water Resources Association
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• v.46 no.2
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• pp.155-169
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• 2013

This study proposes proper forms of empirical formulas for the concentration time and storage coefficient based on their theoretical backgrounds and evaluates several existing empirical formulas by comparing them with the formula proposed in this study. Additionally, empirical formulas for the concentration time and storage coefficient of the Chungju Dam basin were derived using the forms proposed by considering their theoretical backgrounds, and compared with exiting empirical formulas. The results derived are summarized as follows. (1) The concentration time of a basin is proportional to the square of the main channel length, but inversely proportional to the channel slope, as the flood flow is generally turbulent. (2) The storage coefficient is proportional to the concentration time. (3) The comparison results with existing empirical formulas for the concentration time indicates that the empirical formulas like the Kirpich, Kraven (I), Kraven (II), California DoT, Kerby, SCS, and Morgali & Linsley are in line with the form proposed in this study. Among existing empirical formulas for the storage coefficient, the Clak, Russell, Sabol and Jung are found to be well matched to this study. (4) The application results to Chungju Dam basin indicates that among empirical formulas for the concentration time, the Jung, Yoon, Kraven (I), and Kraven (II) show relatively similar results to the observed in this study, but the Rziha shows abnormal results. Among the empirical formulas for the storage coefficient, the Yoon and Hong, Jung, Lee, and Yoon show somewhat reasonable results, but the Sabol shows abnormal results. In conclusion, the empirical formulas for the concentration time and storage coefficient developed in Korea are found to reflect the basin characteristics of Korea better.

• Magazine of the Korean Society of Agricultural Engineers
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• v.29 no.4
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• pp.59-72
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• 1987

Although long-term runoff analysis is important as much as flood analysis in the design of water works, the technological level of the former is relatively lower than that of the latter. In this respect, the precise estimation model for the volume of successive runoff should he developed as soon as possible. Up to now, in Korea, Gajiyama's formula has been widely used in long-term runoff analysis, which has many problems in applying in real situation. On the other hand, in flood analysis, unit hydrograph method has been exclusively used. Therefore, this study aims at trying to apply unit hydrograph method in long-term runoff analysis for the betterment of its estimation. Four test catchment areas were selected ; Maesan area in Namlum river as a representative area of Han river system, Cheongju area in Musim river as one of Geum river system, Hwasun area in Hwasun river as one of Yongsan river system, and Supyung area in Geum river as one of Nakdong river system. In the analysis of unit hydrograph, seperation of effective rainfall was carried out firstly. Considering that effective rainfall and moisture condition of catchrnent area are inside and outside of a phenomenon respectively and the latter is not considered in the analysis, Initial base flow(qb)was selected as an index of moisture condition. At the same time, basic equation(Eq.7) was established, in which qb can take a role as a parameter in relating between cumulative rainfall(P) and cumulative loss of rainfall(Ld). Based on the above equation, computer program for estimation model of qbwas seperately developed according to the range of qb, Developed model was applied to measured hydrographs and hyetographs for total 10 years in 4 test areas and effective rainfall was estimated. Estimation precision of model was checked as shown in Tab- 6 and Fig.8. In the next stage, based on the estimated effective rainfall(R) and runoff(Qd), a runoff distribution ratio was calculated for each teat area using by computerised least square method and used in making unit hydrographs in each test area. Significance of induced hydrographs was tested by checking the relative errors between estimated and measured runoff volume(Tab-9, 10). According to the results, runoff estimation error by unit hydrograph itself was merely 2 or 3 %, but other 2 or 3 % of error proved to be transferred error in the seperation of effective rainfall. In this study, special attentioning point is that, in spite of different river systems and forest conditions of test areas, standardized unit hydrographs for them have very similar curve shape, which can be explained by having similar catchinent characteristics such as stream length, catchinent area, slope, and vegetation intensity. That fact should be treated as important factor ingeneralization of unit hydrograph method.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.1
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• pp.21-30
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• 2017

Soil erosion has been issued in many countries since it causes negative impacts on ecosystem at the receiving water bodies. Therefore best management practices to resolve the problem in a watershed have been developed and implemented. As a prior process, there is a need to define soil erosion level and to identify the area of concern regarding soil erosion so that the practices are effective as they are designed. Universal Soil Loss Equation (USLE) were developed to estimate potential soil erosion and many Geographic Information System (GIS) models employ USLE to estimate soil erosion. Sediment Assessment Tool for Effective Erosion Control (SATEEC) is one of the models, the model provided several opportunities to consider various watershed peculiarities such as breaking of slope length, monthly variation of rainfall, crop growth at agricultural fields, etc. SATEEC is useful to estimate soil erosion, however the model can be implemented with ArcView software that is no longer used or hard to use currently. Therefore SATEEC based on ArcView was rebuild for the ArcGIS software with all modules provided at the previous version. The rebuilt SATEEC, ArcSATEEC, was programmed in ArcPy and works as ArcGIS Toolset and allows considering monthly variations of rainfall and crop growth at any watershed in South-Korea. ArcSATEEC was applied in Daecheong-dam watershed in this study, monthly soil erosion was estimated with monthly rainfall and crop growth variation. Annual soil erosion was computed by summing monthly soil erosion and was compared to the conventional approach to estimate annual soil erosion. The annual soil erosion estimated by the conventional approach and by summing monthly approach did not display much differences, however, ArcSATEEC was capable to provide monthly variation of soil erosion.

• Korean Journal of Environment and Ecology
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• v.18 no.2
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• pp.175-183
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• 2004

They are raising the necessity to prepare the conservational management strategy for the trail on the ridge of the Baekdudaegan where deterioration of natural environment along the trail as the rapid increase of visitors to the Baekdudaegan. The purpose of this study, followed after the Kwon and Lee(2003), is to research the deterioration condition of the trail between Namdeogyusan and Sosagogae on the Baekdudaegan. To accomplish the purpose, not only trail condition such as altitude, entire width, bare width, maximum depth and slope of trail, but also deterioration types of trail were surveyed at the total 182 points for 32.3km in length. Furthermore, impact rating class, which could be effective means to check the step and extent of deterioration process, was judged on each points of trail. Results informs us that the deterioration condition of the trail between Namdeogyusan and Sosagogae is not reached the level of grave concern yet, but some points and sections of trail are in urgent need of the integrated and organized maintenance. And some managerial strategies of trail were proposed in connection with the maintenance for trail on the Baekdudaegan ridge.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.44 no.4 s.316
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• pp.28-35
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• 2007

Airbone laser altimeters have been utilized for 3D topographic mapping of the earth, moon, and planets with high resolution and accuracy, which is a rapidly growing remote sensing technique that measures the round-trip time emitted laser pulse to determine the topography. The traveling time from the laser scanner to the Earth's surface and back is directly related to the distance of the sensor to the ground. When there are several objects within the travel path of the laser pulse, the reflected laser pluses are distorted by surface variation within the footprint, generating multiple echoes because each target transforms the emitted pulse. The shapes of the received waveforms also contain important information about surface roughness, slope and reflectivity. Waveform processing algorithms parameterize and model the return signal resulting from the interaction of the transmitted laser pulse with the surface. Each of the multiple targets within the footprint can be identified. Assuming each response is gaussian, returns are modeled as a mixture gaussian distribution. Then, the parameters of the model are estimated by LMS Method or EM algorithm However, each response actually shows the skewness in the right side with the slowly decaying tail. For the application to require more accurate analysis, the tail information is to be quantified by an approach to decompose the tail. One method to handle with this problem is proposed in this study.

• Korean Journal of Environment and Ecology
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• v.19 no.2
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• pp.130-138
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• 2005

The purpose of this study is to analyze the trail deterioration conditions and to obtain the informations for the desirable maintenance and restoration of the trails in Woraksan National Park. To accomplish the purpose, not only trail condition such as altitude, entire width, bare width, maximum depth and slope of trail, but also deterioration types of trail were surveyed at the total 111 points for 13.5km in length on the four access trails to Yeongbong which is the main peak of Woraksan. Furthermore, impact rating class, which could be effective means to check the step and extent of deterioration process, was judged on each points of trail. Results informs us that the deterioration condition of the trail in Woraksan National Park is not reached the lev- el of grave concern yet, but the active counterplan to change over from the safety-centric facility station to the integrated and organized restoration aiming to natural environment conservation is urgently needed.

• Korean Journal of Environment and Ecology
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• v.16 no.4
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• pp.465-474
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• 2003

According to rapid increase of visitors to the Baekdudaegan, the most important ecosystem in Korea, fur climbing or outdoor recreation, deterioration of natural environment along the trail on the ridge of Baekdudaegan is becoming more serious. The purpose of this study is to research the deterioration condition of the trail between Manbokdae and Bokseongijae on the Baekdudaegan with intent to prepare the conservational management strategy fur the trail on the ridge of Baekdudaegan. To accomplish the purpose, not only trail condition such as altitude, entire width, bare width, maximum depth and slope of trail, but also deterioration types of trail were surveyed at the total 232 points for 28.4km in length. Furthermore, impact rating class, which could be effective means to check the step and extent of deterioration process, was judged on each points of trail. Putting together these results informs us that the deterioration condition of the trail between Manbokdae and Bokseongijae is not reached the level of grave concern yet, but prompt countermeasure to maintain the existing condition has to be considered with regard for the conditions of location and the increasing amounts of use.

• Journal of Korea Water Resources Association
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• v.51 no.9
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• pp.769-782
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• 2018

Estimation of design floods is typically required for hydrologic design purpose. Design floods are routinely estimated for water resources planning, safety and risk of the existing water-related structures. However, the hydrologic data, especially streamflow data for the design purposes in South Korea are still very limited, and additionally the length of streamflow data is relatively short compared to the rainfall data. Therefore, this study collected a large number design flood data and watershed characteristics (e.g. area, slope and altitude) from the national river database. We further explored to formulate a scaling approach for the estimation of design flood, which is a function of the watershed characteristics. Then, this study adopted a Hierarchical Bayesian model for evaluating both parameters and their uncertainties in the regionalization approach, which models the hydrologic response of ungauged basins using regression relationships between watershed structure and model. The proposed modeling framework was validated through ungauged watersheds. The proposed approach have better performance in terms of correlation coefficient than the existing approach which is solely based on area as a predictor. Moreover, the proposed approach can provide uncertainty associated with the model parameters to better characterize design floods at ungauged watersheds.

• Journal of Korea Water Resources Association
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• v.51 no.9
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• pp.795-802
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• 2018

This study investigates the hydraulic characteristics and the delta development processes in the improved-pneumatic-movable weir by considering the standing angle of the weir through laboratory experiments. The delta migration speed decreases rapidly with time. As the ratio of delta height to water depth increases, the dimensionless delta migration speed decreases at the delta point. Therefore, the water depth decreases as the delta height increases. Although the delta volume is large due to the effective height of the delta, the delta migration speed and sediment deposition decreases because of the backwater effect on the delta. On the same bed slope condition, the larger the weir height, the larger the delta volume and the ratio of delta height to delta front length is close to 1.0. The delta development could be suppressed when the weir is high. Therefore, the condition that the weir is high has the suppressing effect on the delta developments.