• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.7182-7188
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• 2015

Recently, to improve manual mapping method, digital mapping using high-resolution camera and laser scanner has increasingly attracted attention and the relevant study is reportedly on the rise. In this study, laboratory and field test which are intended to quantitatively analyze and estimate the weathering degree which is one of the engineering characteristics of tunnel face using laser scanner that integrates high-solution imaging technique have been conducted. In a bid to analyze correlation between reflectance of laser scanner and weathering degree, investigation of the factors influencing on reflectance was carried out. And to minimize the effect on RGB value which is one the critical influential factors on reflectance, modification equation obtained from lab test was proposed. Modification equation proposed in this study was verified by comparing the values before and after correction using the data obtained by scanning. Consequently, weathering index estimated by modified reflectance appeared very similar with dominant weathering degree and weathering ratio monitored at the field.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.4
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• pp.413-420
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• 2010

The ionospheric delay is currently one of the most significant error sources in precise GNSS surveys. The users of single-frequency receivers should apply some kind of ionospheric correction algorithms to remove or model the ionospheric delay. For real-time correction of the ionospheric delay, one can use Klobuchar or NeQuick model provided by navigation messages of GPS and Galileo, respectively. We evaluated the performance of those models by comparing their effectiveness at different seasons and latitudes. For the first test, we computed the vertical total electron content (VTEC) at the permanent GPS site SUWN for four different seasons. As the second test, we picked three sites in Korea (CHLW, SUWN, JEJU) with high, medium, and low latitudes and evaluated the dependency of VTEC on the site latitude. Computed VTEC values were compared with those from the IRI model and Global Ionosphere Maps (GIM). The root-mean-square (RMS) differences of Klobuchar and NeQuick with respect to IRI and GIM were analyzed. As a result, without regard to season and latitude, the RMS differences of NeQuick models were smaller than that of Klobuchar by about 0.01~3.50 TECU.

• The Korean Journal of Applied Statistics
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• v.29 no.4
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• pp.741-752
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• 2016

Numerous studies have shown that normal inverse Gaussian (NIG) distribution adequately fits the empirical return distribution of financial securities. The estimation of parameters can also be done relatively easily, which makes the NIG distribution more useful in financial markets. The maximum likelihood estimation and the method of moments estimation are easy to implement; however, we may encounter a problem in practice when a relationship among the moments is violated. In this paper, we investigate this problem in the parameter estimation and try to find a simple solution through simulations. We examine the effect of our adjusted estimation method with real data: daily log returns of KOSPI, S&P500, FTSE and HANG SENG. We also checked the performance of our method by computing the value at risk of daily log return data. The results show that our method improves the stability of parameter estimation, while it retains a comparable performance in goodness-of-fit.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.473-473
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• 2021

새만금 유역의 하류 평야지대는 농업 관개 및 배수가 제수문의 영향을 받고 있으며, 상류 축산밀집시설에 따라 농업 비점오염원 유입이 수계 환경오염에 미치는 영향을 평가하는 것이 필요하다. 본 연구에서는 새만금 유역의 하류 제수문을 대상으로 유역 모형과 전산유체역학 모형을 이용하여 유입, 유출 그리고 오염원 등의 영향을 분석하고자 한다. SWAT (Soil and water assessment tool)은 유역 모형으로 수문순환 및 비점오염원을 모의하기 위해 개발한 모형이다. CFD(Computational fluid dynamics)는 구조물을 설계하고 유체, 기체 등의 역학을 모의할 수 있다. SWAT 모형을 이용하여 농촌 소유역을 대상으로 하류 제수문 위치를 출구로 지정하여 수문을 모의하고 그 결과자료는 CFD에 입력할 수 있다. CFD는 하류 제수문 구조물을 설계하고 SWAT 모형의 수문자료를 입력하여 제수문의 유입 및 유출 영향을 평가할 수 있다. SWAT 모형 구축을 위해 2015-2018년까지 기상, 수위, 유량 관측자료를 수집하였으며, 보정기간과 검증기간은 각 2년이며, 모형 성능 검증에 사용한 적합성 평가 지수는 R² (Determine coefficient), RMSE (Root mean square error), 그리고 NSE (Nash-sutcliffe efficiency coefficient)를 사용하였다. 모형의 보정은 SWAT-CUP 자동보정프로그램을 사용하였으며, 모형의 보정지수는 NSE를 사용하였고, 1,000회 반복 수행을 통해 매개변수를 최적화하였다. CFD 모형은 제수문의 실제 규격을 바탕으로 동일한 구조를 고려하였으며, 수문조작을 고려하여 유입 및 유출을 모의하였다. 본 연구는 유역차원과 구조물 차원의 모델링을 연계하는 것으로 최근 기후변화에 따라 급격히 변화하는 유역환경에 대처할 수 있는 방안이 될 수 있을 것이며, 제수문 시설을 관리하는 기관에서도 합리적인 운영방안에 대한 기초자료로 기여할 수 있을 것으로 사료된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.474-474
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• 2021

물순환 과정에서의 증발산량은 필수적으로 고려해야 하는 요소이며, 증발산은 기상학적 인자뿐만 아니라 증발 표면 특성 등 복합적인 요인에 의해서 발생한다. 이러한 이유로 실제증발산의 절대량을 추정하는 것은 쉽지 않으며, 특히 수문학적 관점에서 유역단위의 증발산량을 산정하는 데에는 기술적인 한계가 존재한다. 반면 잠재증발산량과 실제증발산량의 보완관계가설을 활용하면 복잡한 수문모델링을 거치지 않고 팬증발량으로부터 유역의 실제증발산을 산정할 수 있다. 본 연구에서는 관측자료를 기반으로 하여 용담댐 유역의 증발산 보완관계를 검증하고자 한다. 실제증발산량(ETA)은 용담댐 내 덕유산 플럭스 타워의 관측자료를 활용하였으며, 잠재증발산량(ETP)으로는 기상관측소에서 관측한 팬 증발량 자료를 활용하였고 습윤증발산량(ETW)은 Priestley-Taylor 공식을 통해 산정하였다. ETW는 수분이 무제한 공급되는 상황에서의 증발산량으로 정의되며, 동시에 ETA 및 ETP와의 상대적 비율로 스케일화하여 보완관계설정에 활용하였다. 대기의 습윤지수(Moisture Index, MI)는 ETA와 ETP간의 상대적 비율로 정의하였다. 이 때 팬 증발량은 기상 및 주변 환경 조건의 영향을 받아 증발량이 과대추정 되는 경향이 있으므로 보정계수를 적용하여 보정한 값을 활용하였다. 보정계수는 FAO Penman-Monteith 식을 활용한 기준증발산량과 팬 증발량의 기울기로 산정하며, 본 연구에서는 보정계수로 0.77을 사용하였다. 또한 ETW 산정 시 적용되는 Priestley-Talyor 계수(α)는 널리 알려진 값인 1.26 대신 유역의 기상조건을 고려하여 0.99를 적용하였다. α 값의 조정을 통해 증발산 보완관계에 대한 E+의 평균 제곱근 오차(RMSE)가 0.685에서 0.075, Ep+의 경우 0.437에서 0.315로 개선되어 용담댐 유역의 증발산 보완관계가 만족할 만한 수준으로 확인되었다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6B
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• pp.515-522
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• 2011

The hydrodynamic models are widely used in the research for analysis of flow characteristics and design of hydraulic structure and river channel. These models need to be calibrated with observed data. But, there are few field data of two-dimensional flow velocity in flood because the direct measurement of the flood flow velocity are very dangerous. For this reason the results of two-dimensional numerical models are usually calibrated and verified with only a few observed data. Moreover, the verification of numerical models for the design flood is usually carried out using the result of one-dimensional model, HEC-RAS. In this study, using the flow velocity profile extracted from the aerial photos of a flood of the Tone River in Japan, two-dimensional numerical models, RAM2 in RAMS, RMA2 in SMS, and one-dimensional numerical model, HEC-RAS which are most widely used in research and design work are verified and the validity for verification of two-dimensional models with HEC-RAS is reviewed. The results showed that the water surface elevation of HEC-RAS, RAM2 and RMA2 models have similar results with observed data. But, the velocity results of RAM2 and RMA2 models in the floodplain have some difference with the velocity from aerial photo analysis. And the velocity result of HEC-RAS has big difference with the sectional averaged value of velocity from aerial photo analysis.

• Korean Journal of Agricultural and Forest Meteorology
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• v.24 no.4
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• pp.244-255
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• 2022

This study estimated and evaluated the high resolution (1km) gridded mountain meteorology data of daily mean, maximum and minimum temperature based on ASOS (Automated Surface Observing System), AWS (Automatic Weather Stations) and AMOS (Automatic Mountain Meteorology Observation System) in South Korea. The ASOS, AWS, and AMOS meteorology data which were located above 200m was classified as mountainous area. And the ASOS, AWS, and AMOS meteorology data which were located under 200m was classified as non-mountainous area. The bias-correction method was used for correct air temperature over complex mountainous area and the performance of enhanced daily coefficients based on the AMOS and mountainous area observing meteorology data was evaluated using the observed daily mean, maximum and minimum temperature. As a result, the evaluation results show that RMSE (Root Mean Square Error) of air temperature using the enhanced coefficients based on the mountainous area observed meteorology data is smaller as 30% (mean), 50% (minimum), and 37% (maximum) than that of using non-mountainous area observed meteorology data. It indicates that the enhanced weather coefficients based on the AMOS and mountain ASOS can estimate mean, maximum, and minimum temperature data reasonably and the temperature results can provide useful input data on several climatological and forest disaster prediction studies.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.10
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• pp.1196-1203
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• 2012

This paper presents a study on the calibration of a C-band HPS(Hongik Polarimetric Scatterometer) system using the DMMCT(Differential Mueller Matrix Calibration Technique). For calibration of the polarimetric scatterometer system, a fully-polarimetric antenna pattern(magnitudes and phase-differences) of the antenna main-beam is measured using a conducting sphere at anechoic chamber. The polarimetric scatterometer system could be accurately calibrated after retrieving its distortions using the DMMCT. Unlike a single-polarimetric system, in a fully-polarimetric system, not only backscattering coefficients but also phase differences are important parameters. This calibrated HPS system can be used to measure accurate Mueller matrices of bare soil surfaces, rice paddies, and vegetation fields. The phase-difference parameters as well as the backscattering coefficients for co- and cross-polarizations can then be obtained. The accuracy of calibration was verified by comparing the measured backscattering coefficients with a scattering model. The measured polarization response of a plowed bare field was also compared with the polarization response which was synthesized using a polarimetric scattering model for verifying the calibration technique.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.4
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• pp.321-329
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• 2013

Despite the advantage of unlimited access, there are insufficient studies for the accuracy and stability of FKP that blocks the spread of the system for various applications. Therefore, we performed a long-term analysis from continuous real-time positioning, and investigated the error characteristics dependent on the size and the surrounding environment. The FKP shows significant changes in the positioning accuracy at different times of day, where the accuracy during daytime is worse than that of nighttime. In addition, the size and deviation of FKP correction may change with the ionospheric conditions, and high correlation between ambiguity resolution rate and the deviation of correction was observed. The receivers continuously request the correction information in order to cope with sudden variability of ionosphere. On the other hand, the correction information was not received up to an hour in case of stable ionospheric condition. It is noteworthy that the outliers of FKP are clustered in their position with some biases. Since several meters of errors can be occurred for kinematic positioning with FKP, therefore, it is necessary to make appropriate preparation for real-time applications.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1086-1092
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• 2012

It has been studied for DGPS/INS(Differential Global Positioning System/Inertial Navigation System) to offer the more precise and reliable navigation data with the aviation industry development. The flight performance evaluation of navigation system is very significant because the reliability of navigation data directly affect the safety of aircraft. Especially, the high-level navigation system, as DGPS/INS, need more precise flight performance evaluation method. The performance analysis is performed by comparing between the DGPS/INS navigation data and reference trajectory which is more precise than DGPS/INS. The GPS receiver, which is capable of post-processed CDGPS(Carrier-phase DGPS) method, can be used as reference system. Generally, the DGPS/INS is estimated the CG(Center of Gravity) point of aircraft while the reference system is output the position of GPS antenna which is mounted on the outside of aircraft. For this reason, estimated error between DGPS/INS and reference system will include the error due to lever arm. In order to more precise performance evaluation, it is needed to compensate the lever arm. This paper presents procedure and result of flight test which includes lever arm compensation in order to verify reliability and performance of DGPS/INS more precisely.