• Journal of Korea Water Resources Association
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• v.54 no.10
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• pp.835-848
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• 2021

In Jeju Island which has peculiarity for its geological features and hydrology system, hydrological factor analysis for the effective water management is necessary. Because in-situ hydro-meteorological data is affected by surrounding environment, the in-situ dataset could not be the spatially representative for the study area. For this reason, remote sensing data may be used to overcome the limit of the in-situ data. In this study, applicability assessment of MOD16 evapotranspiration data, Globas Land Data Assimilation System (GLDAS) based evapotranspiration/soil moisture data, and Advanced SCATterometer (ASCAT) soil moisture product which were evaluated their applicability on other study areas was conducted. In the case of evapotranspiration, comparison with total precipitation and flux-tower based evapotranspiration were conducted. And for soil moisture, 6 in-situ data and ASCAT soil moisture product were compared on each site. As a result, 57% of annual precipitation was calculated as evapotranspiration, and the correlation coefficient between MOD16 evapotranspiration and GLDAS evapotranspiration was 0.759, which was a robust value. The correlation coefficient was 0.434, indicating a relatively low fit. In the case of soil moisture, in the case of the GLDAS data, the RMSE value was less than 0.05 at all sites compared to the in-situ data, and a statistically significant result was obtained as a result of the significance test of the correlation coefficient. However, for satellite data, RMSE over than 0.05 were found at Wolgak and there was no correlation at Sehwa and Handong points. It is judged that the above results are due to insufficient quality control and spatial representation of the evapotranspiration and soil moisture sensors installed in Jeju Island. It is estimated as the error that appears when adjacent to the coast. Through this study, the necessity of improving the existing ground observation data of hydrometeorological factors is emphasized.

• Korean Journal of Agricultural and Forest Meteorology
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• v.23 no.4
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• pp.251-267
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• 2021

Remotely sensed vegetation indices (VIs) are empirically related with gross primary productivity (GPP) in various spatio-temporal scales. The uncertainties in GPP-VI relationship increase with temporal resolution. Uncertainty also exists in the eddy covariance (EC)-based estimation of GPP, arising from the partitioning of the measured net ecosystem CO2 exchange (NEE) into GPP and ecosystem respiration (RE). For two forests and two agricultural sites, we correlated the EC-derived GPP in various time scales with three different near-surface remotely sensed VIs: (1) normalized difference vegetation index (NDVI), (2) enhanced vegetation index (EVI), and (3) near infrared reflectance from vegetation (NIRv) along with NIRvP (i.e., NIRv multiplied by photosynthetically active radiation, PAR). Among the compared VIs, NIRvP showed highest correlation with half-hourly and monthly GPP at all sites. The NIRvP was used to test the reliability of GPP derived by two different NEE partitioning methods: (1) original KoFlux methods (GPP_Ori) and (2) machine-learning based method (GPP_ANN). GPP_ANN showed higher correlation with NIRvP at half-hourly time scale, but there was no difference at daily time scale. The NIRvP-GPP correlation was lower under clear sky conditions due to co-limitation of GPP by other environmental conditions such as air temperature, vapor pressure deficit and soil moisture. However, under cloudy conditions when photosynthesis is mainly limited by radiation, the use of NIRvP was more promising to test the credibility of NEE partitioning methods. Despite the necessity of further analyses, the results suggest that NIRvP can be used as the proxy of GPP at high temporal-scale. However, for the VIs-based GPP estimation with high temporal resolution to be meaningful, complex systems-based analysis methods (related to systems thinking and self-organization that goes beyond the empirical VIs-GPP relationship) should be developed.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1885-1889
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• 2006

제주지역은 대륙과 해양을 연결하는 요충지로서 한라산을 중심으로 동서사면은 $3{\sim}5^{\circ}$의 완만한 경사를 이루고 있다. 연평균 강우량은 1,975mm로서 국내 최다우 지역이나 제주도의 지질 특성상 도내 대부분의 지역이 투수성이 높은 다공질 현무암으로 구성되어 있는 관계로 지표수의 발달이 미약한 반면 지하수가 풍부하게 부존되어 있으며 기저지하수, 준 기저지하수, 상위지하수, 기반암지하수로 이루어져 있다. 최근 우리나라의 교토의정서 비준으로 인한 온실가스 감축이 불가피함에 따라 대체 재생가능한 에너지를 이용한 풍력발전시대가 도래하고 있으며, 제주 행원풍력발전단지에 설치된 총 15기 발전장치의 현실성과 경제성 입증을 통해 제주지역의 풍력에너지를 이용한 지하수 취수시스템을 제안하였다. 본 연구는 제주, 고산, 서귀포, 성산포지역에 대한 제주지방기상청 연평균 풍속자료$(2004{\sim}2005)$를 통하여 대상지역내 적용 가능한 로터(Roter), 나셀(Nacelle), 타워(Tower), 발전기를 포함한 발전장치를 선정하였으며, 공기역학적(Aerodynamic)특성에서 전기에너지로 변환한 풍력에너지를 지하수 취수시스템으로 적용하기까지의 전력공급절차를 도출하였다. 또한 생산되어진 풍력에너지 용량에 적용 가능한 수중.육상모터펌프를 산정하여 '제주도 지하수개발.이용시설 설치 및 관리기준(2004)'에서 제시한 구조도를 바탕으로 대상지역내 지하수위를 고려한 지하수 취수시스템을 도시하였다. 제주도는 지형 및 지질적인 특성상 수자원을 지하수에 의존할 수밖에 없는 특수한 지역이므로 2002년말 통계를 살펴보면 생활용, 공업용, 농업용으로 각각 57만$m^2$, 11만$m^2$, 56만$m^2$를 포함한 1일 최대 124만$m^2$의 지하수를 사용하고 있다. 따라서 풍력에너지를 이용한 지하수 취수시스템을 도입하여 재생가능한 에너지이용 효과와 세계인이 공감하는 청정한 관광자원으로 활용 가능할 것이라 판단된다.

• Korean Journal of Remote Sensing
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• v.27 no.2
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• pp.131-140
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• 2011

In this study, temporal variations of the Advanced Microwave Scanning Radiometer E (AMSR-E) soil moisture products were evaluated using ground based measurements from the Haenam flux monitoring network site for two years (2004 and 2006). Even if there were major comparison issues including spatial resolutions, AMSR-E soil moisture production showed a great potential to replicate temporal variability patterns with ground based measurements. Additional intensive validation efforts should be conducted at a variety of field conditions including vegetation type for better utilization of remotely sensed soil moisture and understanding of the land surface-atmosphere interactions in the view of hydrometeorology.

• Atmosphere
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• v.26 no.3
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• pp.483-492
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• 2016

We have examined the random error of eddy covariance (EC) measurements on the basis of two-tower approach during daytime. Two EC towers were placed on the grassland with different vegetation density near Gumi-weir. We calculated the random error using three different methods. The first method (M1) is two-tower method suggested by Hollinger and Richardson (2005) where random error is based on differences between simultaneous flux measurements from two towers in very similar environmental conditions. The second one (M2) is suggested by Kessomkiat et al. (2013), which is extended procedure to estimate random error of EC data for two towers in more heterogeneous environmental conditions. They removed systematic flux difference due to the energy balance deficit and evaporative fraction difference between two sites before determining the random error of fluxes using M1 method. Here, we introduce the third method (M3) where we additionally removed systematic flux difference due to available energy difference between two sites. Compared to M1 and M2 methods, application of M3 method results in more symmetric random error distribution. The magnitude of estimated random error is smallest when using M3 method because application of M3 method results in the least systematic flux difference between two sites among three methods. An empirical formula of random error is developed as a function of flux magnitude, wind speed and measurement height for use in single tower sites near Nakdong River. This study suggests that correcting available energy difference between two sites is also required for calculating the random error of EC data from two towers at heterogeneous site where vegetation density is low.

• Journal of the Korean Solar Energy Society
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• v.34 no.2
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• pp.60-65
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• 2014

A meteorological(met) tower is the first structure installed during the planning stages of offshore wind farm. The purpose of this paper is to design the met tower with tripod bucket type support structure and to install the sensors. The support structure consist of a central steel shaft connected to three cylindrical steel suction buckets which is more cheaper than monopile or jacket type. And the remote wind condition sensors and marine monitoring equipment, including adcp, pressure type tide gauge, wave height sensors, and scour sensors, remote power supply are installed. The manufactured met tower constructed on sea area which is in front of Gasa island. All of functions of met tower showed normal operation conditions and the wind data got by remote data collection system successfully.

• Journal of the Korean Solar Energy Society
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• v.37 no.6
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• pp.103-114
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• 2017

Radiation energy budget was analyzed using observation data from the Weather Information Service Engine (WISE) energy flux tower on the Seoul metropolitan area. Among observation data from the 13 energy flux towers, we used meteorological variables, radiation data (upward and downward short wave, upward and downward long wave, net short wave, net long wave and net radiation), albedo and emissivity for 15 months from July 2016 to September 2017. Although Gajwa (205) and Ttuksumm (216) sites located in urban, the albedo was relatively high due to the surround environment by glass wall buildings and the Han river around the sites. And Bucheon (209) site located in the suburb represented generally low emissivity. As a result, the albedo decreased and the emissivity increased in the city center. In the Seoul metropolitan area, the net radiation energy is $73.9W/m^2$ that the radiation budget of the surface is absorbed into the atmosphere. According to WISE observation data, it can be seen that observation at each sites are influenced by the surrounding environment.

• Journal of the Korean Solar Energy Society
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• v.31 no.5
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• pp.1-8
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• 2011

In this study, we performed a sensitivity analysis to see how the true north error of a wind direction vane installed to a meteorological mast affects predictions of the annual-average wind speed and the annual energy production. For this study, two meteorological masts were installed with a distance of about 4km on the ridge in complex terrain and the wind speed and direction were measured for one year. Cross predictions of the wind speed and the AEP of a virtual wind turbine for two sites in complex terrain were performed by changing the wind direction from $-45^{\circ}$ to $45^{\circ}$with an interval of $5^{\circ}$. A commercial wind resource prediction program, WindPRO, was used for the study. It was found that the prediction errors in the AEP caused by the wind direction errors occurred up to more than 20% depending on the orography and the main wind direction at that site.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.26-26
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• 2018

기후변화로 인한 홍수, 가뭄 등의 자연재해가 빈번히 발생함에 따라서, 수자원의 변동성이 심각해짐에 따라서 물 부족에 대한 관심이 대두되고 있다. 특히, 수문분야에서 수자원의 확보 및 효율적 관리에 대한 중요성 및 관심이 높아지고는 있으나, 물 순환에 대한 이해 및 분석에 대한 부분은 아직 계속적으로 연구할 필요성이 있다. 물 순환에서 다른 수문기상인자들에 비해 직접적인 관측이 어려운 실제증발산은 단순 가정 및 경험식, 또는 물수지 방정식을 통해 어림되어 계산되어 진다. 지상에서 실제증발산을 관측하기 위해 에디 공분산 기반의 플럭스 타워(flux tower)를 이용하여 한 지역(지점)에서의 정량적인 관측이 이뤄지고 있으나, 공간적인 관측은 이뤄지고 있지 않는 문제점을 가지고 있다. 따라서, 기술이 발전함에 따라 다양한 물리식 기반의 재분석자료(reanalysis data)/인공위성(satellite)기반의 실제증발산에 대한 자료가 산출되어진다. 그렇지만, 다양한 물리식 기반으로 산출되는 결과는 알고리즘의 특성상 오차가 발생할 수 있다. 이러한 방법을 해결하기 위하여 다양한 합성 방법을 이용하여 각 알고리즘에서 오차를 보정 및 개선한 최적의 실제증발산 결과를 필요로 하게 된다. 이 연구에서는 재분석/인공위성 기반의 8일 단위 실제증발산 자료를 활용하여 두 가지의 합성 방법(simple taylor skill score, maximize r)을 이용하여 개선된 실제증발산 결과를 산출하기 위하여, 2005년부터 2014년까지의 호주에서의 실제증발산에 대한 합성 결과를 나타내었다. 전반적으로 두 방법으로 산정된 결과는 기존의 결과에 비해 오차가 상당히 개선된 것을 확인 할 수 있었으며, 특히, 다양한 자료를 이용하여 합성하는 방법인 simple taylor skill score방법이 maximize r의 방법에 비해 보다 오차 및 상관성이 높은 것을 확인 할 수 있다. 본 연구에서 합성 방법을 이용하여 기존의 자료에 비해서 개선된 결과를 산정할 수 있는 것을 확인하였고, 향후 가뭄에 직접적으로 연관성을 가진 합성 증발산 자료를 활용하여 가뭄 분석의 신뢰성을 향상시킬 수 있을 것으로 기대된다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.35 no.6
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• pp.146-154
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• 2023

In this study, the peak wave period T_p and mean wave period T₀₂ and T_{m-1, 0}, which are major parameters for classifying ocean characteristics, were calculated using water surface elevation data observed from the second west coast oceanographic and meteorological observation tower. In addition, the ratio of abnormal data, correlation analysis, and optimal probability density function were estimated. In the case of T_p among the calculated representative periods, the proportion of abnormal data was 5.73% and 0.67% at each point, and T₀₂ was 4.35% and 0.01%. T_{m-1, 0} was found to be 2.82% and 0.03%. Meanwhile, as a result of analyzing the relationship between T₀₂ and T_p, the relationship was calculated to be 0.53 and 0.63 for each point. The relationship between T_{m-1, 0} and T_p was 1.15 and 1.32, respectively, and T₀₂, T_{m-1, 0} was 1.18 and 1.22. As a result of estimating the optimal probability density function of the calculated representative period, T_p followed the 'Log-normal' and 'Normal' distributions at each point, and T₀₂ was 'Gamma', 'Normal' distribution and T_{m-1, 0} showed that 'Log-normal' and 'Normal' distribution were dominant, respectively. It is decided that these results can be used as basic data for wave analysis conducted on the west coast.