• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.2
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• pp.155-165
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• 2002

This paper presents a case study on the construction of a long tunnel named as "Solan tunnel", which connects between Mt. Dongbaek station and Dokye station in the Youngdong Railroad. The tunnel will be the longest tunnel with length of 16.4 km in Korea when completed. The tunnel site is located in a complex geological region with faults, cavities and coal measures. In construction of adit No. 2, geophysical investigation methods such as electrical resistivity method and GPR(Ground Penetration Radar) were used to detect faults, cavities and coal measures in advance with some success. The geophysical investigation results and in-situ boring data were used as feedback to improve tunnel reinforcement design. Also, the tube umbrellas of grouted steel pipes were found to have a good reinforcement and grouting effects in zones of faults, cavities. In zones of coal measures, swellex rockbolts with mortar grouting were verified as successful.

• Geomechanics and Engineering
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• v.16 no.3
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• pp.285-293
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• 2018

In densely populated urban areas with a large amount of infrastructure, ground subsidence events can result in massive casualties and economic losses. In South Korea, the incidence of ground subsidence in urban areas has increased in recent years and the number of underground cavities suspected of causing such events has significantly increased. Therefore, it is essential to develop techniques to prevent the occurrence of underground and ground subsidence. In this study, a field test, laboratory test, and numerical analysis were conducted to determine the optimal compaction degree of the upper support layer of any underground cavity below the level of sewer pipes in order to prevent such cavities from collapsing and leading to ground subsidence accidents. During the field test, an underground cavity was simulated using ice, and the generation of the cavity was confirmed using ground penetrating radar. The ground investigation was performed using a cone penetration test, and the compaction of the ground where ground subsidence occurred was evaluated with a laboratory test. The behaviour of the ground under various conditions was predicted using a numerical analysis based on the data obtained from the field test and previous studies. Based on these results, the optimal compaction degree of the ground required to prevent the underground cavity from causing ground subsidence was predicted and presented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.2
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• pp.184-191
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• 2012

Aerodynamic analysis(DATCOM) and radar cross section(RCS) analysis(POFACETS) were integrated for the air-to-surface missile concept design using a design framework. The missile geometry was defined based on the CAD(CATIA) for synchronizing the manufacturing with design processes. Aero/RCS analyses were linked with the CAD process under the ModelCenter framework in order to receive the geometry data automatically. The missile design baseline configuration was selected from ROC(requirement of capability). Then the RCS minimization was performed subject to thelargerthebetter constraint of the missile lift-to-drag ratio. This study demonstrated that various design strategies can be performed efficiently about many missile configurations using this design framework in the missile conceptual design phase.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.281-285
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• 2007

본 연구에서는 보다 신뢰성 있고 정확한 정량적 강우예측자료를 생성하기 위하여 레이더강우 및 강우수치예보자료를 합성하는 기법을 제시하였고, 레이더 전처리 및 예측시스템, GIS와 연계한 물리적기반의 분포형모형인 Vflo모형 등 최신 수자원 IT기술을 활용하여 홍수기 돌발홍수에 대응한 초단기 정량적 강우-유출예측을 목적으로 향후 실시간으로 적용 가능한 분포형유출예측시스템의 기반을 구축하고자 하였다. 대상유역은 국지적인 고해상도 지형효과를 고려한 QPM이 개발되어 있는 금강권역의 용담댐유역이며, 예측 강우에 대한 호우사상은 2005년 이후 발생한 3개 강우사상을 대상으로 하였다. 한편, 기상 레이더 자료로부터 산정된 강수량의 수문학적 적용을 위하여 DEM, 토지피복도, 토양도 등의 기본 GIS자료들을 수집 및 구축하였고 물리적기반의 분포형모형(Vflo)의 입력인자로 사용하기 위한 12개의 공간분포형 수문매개변수들을 대표적인 GIS 소프트웨어인 ArcGIS 및 ArcView를 활용하여 추출하였으며, Vflo모형의 현업 적용가능성을 오프라인 상에서 검증해보았다. 모형 검증결과, GIS를 이용한 지형, 토양, 토지피복과 같은 물리적 특성을 사용한 모형의 초기 설정을 향상시킴에 의해 첨두유량, 유출량, 첨두도달시간차 등에서 만족할만한 결과를 보여주었다고 사료된다. 레이더 및 수치예보자료와 합성한 4가지의 형태(QPE, JQPE, QPM, BQPF)의 분포형 입력강우를 이용하여 적용해 본 결과 Nowcasting기법을 이용한 JQPF는 자료의 특성상 초기 1시간30분동안은 비교적 양호한 결과를 얻었으나 3시간 전후로 가면서 예측강우의 질이 저하되기 시작하였으나 QPM을 합성함으로써 생산한 BQPF는 보다 신뢰성있고 양호한 결과를 얻을 수 있었다. 이러한 결과들은 향후 정량적 분포형강우 예측을 이용한 실시간 홍수유출 예측시 댐운영자는 리드타임(홍수선행시간)을 충분히 확보함으로서 안정적이고 예측 가능한 홍수조절을 하는데 도움을 줄 수 있을 것으로 기대된다. 이와 같이 다양한 단기저수지 유입량의 예측정보 제공으로 다목적댐 저수지 운영모형의 효용성을 제고하여 향후 실제 저수지 유입량 예측에 이용함으로써 저수지 단기운영효율 개선에 기여할 수 있을 것으로 사료된다.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.18 no.4
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• pp.15-27
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• 2015

The objectives of this study are to analyze the quantitative ecological principal components of Korean Peninsula using the multivariate spatial environmental datasets and to compare the ecological difference between South and North Korea. Ecological maps with GIS(Geographical Information System) are constructed by PCA(Principal Component Analysis) based on seventeen raster(cell based) variables at 1km resolution. Ecological differences between South and North Korea are extracted by Factor Analysis using ecosystem maps masked from Korean ones. Spatial data include SRTM(Shuttle Radar Topography Mission), Temperature, Precipitation, SWC(Soil Water Content), fPAR(Fraction of Photosynthetically Active Radiation) representing for a productivity, and SR(Solar Radiation), which all cover Korean peninsula. When it performed PCA, the first three scores were assigned to red, green, and blue color. This color triplet indicates the relative mixture of the seventeen environmental conditions inside each ecological region. The first red one represents for 'physiographic conditions' worked by high elevation and solar radiation and low temperature. The second green one stands for 'seasonality' caused by seasonal variations of temperature, precipitation, and productivity. The third blue one means 'wetness condition' worked by high value such as precipitation and soil water contents. FA extraction shows that South Korea has relatively warm and humid ecosystem affected by high temperature, precipitation, and soil water contents whereas North Korea has relatively cold and dry ecosystem due to the high elevation, low temperature and precipitation. Results would be useful at environmental planning on inaccessible land of North Korea.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.91-97
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• 2004

The first Korean liquid propellant rocket KSR-III successfully finished its flight test on Nov. 28, 2002. Herein, we summarize the results of range safety system operation which is employed for the first time in flight tests of rockets developed by Korea Aerospace Research Institute(KARI). During the flight, safety-critical flight data including instantaneous impact points are monitored in realtime by range safety officers utilizing Range Safety Display Systems. The recorded screen of the display system is presented for the explanation of safety operation. In addition, comparisons are made between onboard navigation system based and radar based results in calculating instantaneous impact points, and also errors from the finally recorded impact point are described.

• Korean Journal of Optics and Photonics
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• v.27 no.4
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• pp.133-142
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• 2016

This paper presents the design and simulation of a three-dimensional pixel-by-pixel scanning light detection and ranging (LIDAR) system with a microelectromechanical system (MEMS) scanning mirror and direct sequence optical code division multiple access (DS-OCDMA) techniques. It measures a frame with $848{\times}480$ pixels at a refresh rate of 60 fps. The emitted laser pulse waves of each pixel are coded with DS-OCDMA techniques. The coded laser pulse waves include the pixel's position in the frame, and a checksum. The LIDAR emits the coded laser pulse waves periodically, without idle listening time to receive returning light at the receiver. The MEMS scanning mirror is used to deflect and steer the coded laser pulse waves to a specific target point. When all the pixels in a frame have been processed, the travel time is used by the pixel-by-pixel scanning LIDAR to generate point cloud data as the measured result.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.6
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• pp.1121-1126
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• 2017

Various studies such as INS(: Inertial Navigation System) are conducting to estimate the position of UAV, because the GPS information of UAV is at risk like the GPS jamming. The position estimation using DoA and RTT are used to apply many radar systems, and that process can be applied in datalink of UAV. The general monopulse feed in UAV datalink is Multi-horn, because of the wide BW(: Band Width) and frequency range. And it needs wide SNR range of tracking because of the limited transmit power of airborne unit. The estimation error of position increase at low SNR, and the DoA is valid in only 3dB beam width but high SNR causes false of mainlobe detection because of large sidelobe. In this paper, We propose the method to achieve higher accuracy of DoA estimation on low SNR and review some idea that able to detect mainlobe.

• Journal of Environmental Science International
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• v.26 no.7
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• pp.827-836
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• 2017

Freezing rain is a phenomenon when precipitation falls as a liquid rain drop, but freezes when it comes into contact with surfaces or objects. In this study, we investigated the predictability of freezing rain and its characteristics, which are strongly related with the occurrence of black ice using synoptic scale meteorological observation data. Two different cases occurred at 2012 were analyzed and in the presented cases, freezing rain often occurs in the low-level low pressure with the warm front. The warm front due to the lower cyclone make suitable environment in which snow falling from the upper layer can change into supercooled water. The $0^{\circ}C$ temperature line to generate supercooling water is located at an altitude of 850 hPa in the vertical temperature distribution. And the ground temperature remained below zero, as is commonly known as a condition for black ice formation. It is confirmed that the formation rate of freezing rain is higher when the thickness after 1000-850 hPa is 1290-1310 m and the thickness of 850-700 hPa layer is larger than 1540 m in both cases. It can also be used to predict and estimate the generation of freezing rain by detecting and analyzing bright bands in radar observation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.9
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• pp.1100-1106
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• 2012

This paper has presented the analysis of the micro-Doppler signatures scattered from the blades of the rotating propeller using the modified HHT method, one of the joint time-frequency analysis methods. The field scattered from the blade edge of the propeller was calculated using equivalent current method(ECM). After the acquisition of the scattered field data in the time domain, the modified HHT method was applied to analyze the micro-Doppler signature. The analysis results showed not only a good agreement with the realistic dynamic characteristic of the blade but also sinusoidally varing characteristics of the micro-Doppler signatures generated from rotating objects. It could be concluded that the joint time-frequency analysis via the modified HHT provided the discriminative characteristics for recognizing a small aircraft target with small RCS value.