• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3B
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• pp.233-242
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• 2010

SEBAL (Surface Energy Balance Algorithm for Land) developed by Bastiaanssen (1995) is an image-processing model comprisedof twenty-five sub models that calculates spatial evapotranspiration (ET) and other energy exchanges at the surface. SEBAL uses image data from Landsat or other satellites measuring thermal infrared radiation, visible and near infrared. In this study, the model was applied to Gyeongancheon watershed, the main tributary of Han river Basin. ET was computed on apixel-by-pixel basis from an energy balance using 4 years (2001-2004) Landsat and MODIS images. The scale effect between Landsat (30 m) and MODIS (1 km) was evaluated. The results both from Landsat and MODIS were compared with FAO Penman-Monteith ET. The absolute errors between satellite ETs and Penman-Monteith ET were within 12%. The spatial and temporal characteristics of ET distribution within the watershed were also analyzed.

• Journal of Korea Water Resources Association
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• v.32 no.6
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• pp.721-730
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• 1999

A Grid-based daily evapotranspiration(ET) prediction model which calculates temporal and spatial ET with a complementary relationship of Morton(1983) was developed. The model was programmed by C-language and uses ASCII formatted map data of DEM(Digital Elevation Model) and land use. Daily ET within the watershed is calculated and the results of temporal variations and spatial distributions of ET are presented by using GRASS(Geographic Resources Analysis Support System). To verify the applicability of the model, it was applied to the part of Bocheong stream basin (76.5$\textrm{km}^2$) located in the upstream of Dacheong Dam watershed. The result shows that the estimated evapotranspiration in 1995 was 766.1mm and 22% increased after correction radiation for slope and area.

• Journal of the Korean Association of Geographic Information Studies
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• v.7 no.4
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• pp.88-97
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• 2004

A Grid-based distributed evaporation prediction model which calculates temporal and spatial evaporation with a heat balance method was developed. And, the model was considered as the integration with distributed hydrological model in near future. 'This model was programmed by fortran language and used ASCII formatted map data of DEM (Digital Elevation Model) and land cover map extracted by remote sensing data. Also, temporal variations and spatial distributions of evaporation are presented by using GIS. To verify the applicability of the model, it was applied to the Shonai river basin ($532km^2$) which has sufficient meteorological and hydrological data, Japan. The result shows that the estimated mean annual evaporation was 825.4mm, and this value is estimated as suitable things in considering rainfall and discharge data in study area.

• Journal of Korea Water Resources Association
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• v.55 no.11
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• pp.979-989
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• 2022

In hydrological surveys, observation through representative location is essential due to temporal and spatial limitations and constraints. Regarding the use of hydrological data and the accuracy of the data, there are still insufficient observatories to be used in a specific watershed. In addition, since there is virtually no standard for the location of the current evapotranspiration, this study proposes a method for determining the location of the evapotranspiration. To determining the location of evapotranspiration, a grid is selected in consideration of the operating range of the Flux Tower using the eddy covariance measurement method, which is mainly used to measure evapotranspiration. The grid of representative location was calculated using the factors affecting evapotranspiration and satellite data of evapotranspiration. The grid of representative location was classified as good, fair, and poor. As a result, the number of good grids calculated was 54. It is judged that the classification of the grid has been achieved regarding topography and land use as a characteristic that appeared in the classification of the grid. In particular, in the case of elevation or city area, there was a large deviation, and the calculated good grid was judged to be a group between the two distributions.

• Journal of the Korean Association of Geographic Information Studies
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• v.8 no.4
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• pp.1-13
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• 2005

In the process of a hydrology circulation, evapotranspiration is considered a very important factor to build a plan for the development of water resources and to operate water resources system. This study purposes to estimate daily potential evapotranspiration quantity in consideration of energy factors of the surface by using spatial information such as Landsat TM (ETM+) data, DEM and Landcover. Kyounan-cheon, Han River is selected as a target area, and landcover is divided by vegetation and non-vegetation covered area. Penman-Monteith equation which considers leaf-area index is used to estimate potential evapotranspiration quantity of vegetation covered area. The combination method (energy burget and aerodynamic method) is used in non-vegetation covered area. Among the input data for estimating potential evapotranspiration, NDVI, SR and Albedo is formed by Landsat, TM and ETM+ from 1986 through 2002. ground heat flux is estimated by using NDVI distribution map, LAI distribution map is drawn by using SR distribution map. The result of estimation shows that the average potential evapotranspiration in the whole basin is about 1.8-3.2mm/day per each cell. THe results of estimating potential evapotranspiration quantity by each landcover are as follows; water surface 3.6-4.9mm/day, city 1.4-3.1mm/day, bareland 1.4-3.5mm/day, grassland 1.7-3.7mm/day, forest 1.7-3.0mm/day and farmland 1.8-3.6mm/day. The potential evapotranspiration quantity is underestimated in comparison with observed evaporation data by evaporation pan, but it is considered that it has physical propriety.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.100-100
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• 2021

IPCC 5차 보고서에 따르면 지구 평균 기온상승은 저위도 보다 극지방에서 더욱 뚜렷하게 나타나며 이러한 기후변화는 극지 생태계의 변화를 초래한다. 이러한 기후변화에 따른 극지 생태계의 변화를 분석 및 예측하기 위하여 지면-생태계 모형을 구축하고 극지방 생태계, 수문 및 탄소 순환 등을 모의하는 연구들이 많이 진행되고 있다. 최근 극지 지역에서는 기후변화로 인하여 화재 발생 빈도가 증가하고 있으며, 이로 인하여 극지 생태계뿐 아니라 물순환에 많은 영향을 미치고 있다. 하지만 지면-생태계 모형안의 화재 시뮬레이션은 화재의 원인 파악의 부족, 입력자료의 부족, 화재 역학 이해의 부족 등의 한계가 존재한다. 본 연구에서는 2001~2012년 동안 위성에서 관측된 화재면적 자료인 Global Fire Emissions Database (GFED) v4 자료와 지면-생태계 모형인 NCAR Community Land Model (CLM)-biogeochemistry (BGC) 와의 실시간 융합을 통하여 기존 화재 시뮬레이션의 한계점을 보완하고자 하였다. 기존 CLM-BGC 모형을 통한 증발산량, 화재 자료-모형의 융합을 통한 증발산량 결과와 Moderate Resolution Imaging Spectroradiometer (MODIS) 증발산량 자료와의 비교를 통하여 증발산량 모의에 화재의 중요성을 분석하고자 한다. 또한, 유출량 뿐만 아니라 토양수분의 변화를 시·공간적 변화를 분석함으로써 화재가 극지방 물순환에 미치는 영향을 나타내었다. 또한, 본 연구를 통하여 미래 기후변화에 따른 극지방의 생태계 및 물순환을 모의하기 위하여 화재 시스템 구축의 중요성을 제시하였다.

• Journal of Korean Society for Geospatial Information Science
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• v.14 no.2 s.36
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• pp.55-62
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• 2006

Droughts have been an important factor in disaster management in Korea because she has been grouped into nations of lack of water. Satellite imagery can be applied to droughts monitoring because it can provide periodic data for large area for long time. This study aims to present a process to analyze droughts in large area using satellite imagery. We estimated evapotranspiration in large area using NDVI data acquired from satellite imagery. For satellite imagery, we dealt with MODIS data operated by NASA. The evapotranspiration estimated from satellite imagery was combined with precipitation data and potential evapotranspiration data to estimate water balances. Using water balances we could analyze droughts effectively in our object area. As the result of this study, we could increase the usability of satellite imagery, especially in droughts analysis.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.72-72
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• 2021

가뭄은 수개월, 수년 이상에 걸쳐 서서히 발생 및 지속되며, 식생에 대한 피해가 발생할 때까지 확실한 인식이 어렵다. 최근에는 기후변화로 인하여 가뭄의 발생빈도가 증가하고 있으며, 기상 이상에 따른 다양한 형태의 가뭄이 발생하고 있다. 미국에서 정의한 'Flash Drought'는 비교적 짧은 기간 동안 표면온도의 상승과 비정상적으로 낮고 빠르게 감소하는 토양수분으로 인하여 식생에 대한 극심한 스트레스를 유발하면서 광범위한 작물 손실 및 용수공급 감소 등에 대한 피해를 야기하는 가뭄이다. 국내에서는 Flash Drought에 대한 모니터링이 활성화되지 않았기 때문에 본 연구에서는 '돌발가뭄'이라는 새로운 정의를 제시하면서 토양수분, 증발산량, 강수량, 기온 등의 가뭄 관련 주요인자를 활용하여 국내에서 발생한 돌발가뭄 (Flash Drought)를 감지하고 분석하고자 하였다. 돌발가뭄을 분석하기 위하여 선행연구에서 제시한 가뭄 관련 주요인자 기준 유형, 증발산량 기반 가뭄지수를 활용한 유형 등을 활용하였으며, 지상관측자료로는 국내 76개 종관기상관측 자료를 활용하였다. 또한, 토양수분 자료는 GRACE (Gravity Recovery and Climate Experiment) 위성영상 자료를 취득한 후 5 km 공간해상도 자료로 활용하였다. 가뭄지수의 경우 증발산 기반 가뭄지수 중 표준강수증발산지수 SPEI (Standardized Precipitation Evapotranspiration), 증발스트레스지수 ESI (Evaporative Stress Index) 등을 활용하여 국내 돌발가뭄 유형에 대한 분석에 적용하였다. 본 연구를 통하여 아직 명확하게 정의되지 않은 돌발가뭄에 대한 유형별 분석 및 국내 돌발가뭄의 수문기상학적 특성을 분석하고자 한다.

• Korean Journal of Agricultural and Forest Meteorology
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• v.21 no.4
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• pp.229-237
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• 2019

This study was conducted to estimate annual reference evapotranspiration (ET₀) for the agro-climatic zones for rice paddy fields in South Korea between 1980 and 2015. The daily ET₀ was estimated by applying the Penman-Monteith method to meteorological data from 61 weather stations provided by Korean Meteorological Administration (KMA). The average of annual ET₀ from 1980 to 2015 was 1334.1±33.89 mm. The ET₀ was the highest at the Southern Coastal Zone due to their higher air temperature and lower relative humidity. The ET₀ had significantly increased with 2.81 mm/yr for the whole zones over 36 years. However, the change rate of it was different among agro-climatic zones. The annual ET₀ highly increased in central zones and eastern coastal zones. In terms of correlation coefficient, the temporal change of the annual ET₀ was closely related to variations of four meteorological factors (i.e., mean, minimum temperatures, sunshine duration, and relative humidity). The results demonstrated that whole Korean agro-climatic zones have been undergoing a significant change in the annual ET₀ for the last 36 years. Understanding the spatial pattern and the long-term variation of the annual ET₀ associated with global warming would be useful to improve crop and water resource managements at each agro-climatic zone of South Korea.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.95-95
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• 2021

전 세계 담수 자원의 예측 및 관리에 있어서 유출량 변화의 예측은 중요하다. 하지만 강수량 대비 유출량의 비율인 유출율이 수자원 시스템에 중요한 영향을 미치는지에 대한 여부는 여전히 불분명하다. 본 연구에서는 전 세계의 1,636개 관측소에서 관측된 유출량과 강수량 자료를 이용하여 최근 60년 (1956-2015) 동안 유출량, 강수량, 증발산량의 관계에 있어서 유출율의 역할에 관해 연구하였다. 수문 기후학적으로 습한 지역과 건조한 지역을 구분할 수 있는 임계값으로 유출율을 사용할 수 있다는 점을 Budyko 공간에서 적용하여 건조 지수와의 비교를 통해 발견할 수 있었다. 유출량 변화에 대한 상세한 분석을 위해 강수량 및 증발산량 변화율에 따라 6가지의 범주를 설정하였고 그 결과 대부분의 관측소에서는 강수량의 변화와 일관된 방향으로 유출량이 변화하는 것으로 밝혀져 유출량의 변화는 강수 변화에 더 민감하다는 결론을 얻었으며 모든 범주에 있어서 유출율은 강수량과 증발산량의 변화에 의한 유출량 변화의 크기에 상당한 영향이 있음이 밝혀졌다. 본 연구의 결과들을 통해 우리는 기후 변화에 따른 유출량 변화에 대한 예측성 향상에 있어서 유출율에 대한 물리적인 이해가 잠재적인 주요한 요소라고 제안한다. 토지 피복 및 토지 이용과 같은 인위적 영향은 유출율을 직접 감소 또는 증가시켜 유출량의 민감도를 변화시킬 수 있다. 본 연구에서 제안된 수치적인 접근 방식은 수자원 가용성에 대한 기후 변화 및 인위적 영향을 완화하기 위해 실행 가능한 정보를 제공할 것으로 보인다.