• Korean Journal of Remote Sensing
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• v.38 no.6_1
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• pp.1301-1314
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• 2022

Normalized Difference Vegetation Index (NDVI) is utilized as an indicator to represent the vegetation condition on the land surface in various applications such as land cover, crop yield, agricultural drought, soil moisture, and forest disaster. However, satellite optical sensors for visible and infrared rays cannot see through the clouds, so the NDVI of the cloud pixel is not a valid value for the land surface. This study proposed a real-time correction of the underestimation noise for GEO-KOMPSAT-2A (GK2A) daily NDVI and made sure its feasibility through the quantitative comparisons with Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI and the qualitative interpretation of time-series changes. The underestimation noise was effectively corrected by the procedures such as the time-series correction considering vegetation phenology, the outlier removal using long-term climatology, and the gap filling using rigorous statistical methods. The correlation with MODIS NDVI was higher, and the difference was lower, showing a 32.7% improvement compared to the original NDVI product. The proposed method has an extensibility for use in other satellite products with some modification.

• Korean Journal of Remote Sensing
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• v.38 no.5_3
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• pp.901-912
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• 2022

The frequency of disasters is increasing due to global climate change, and unusual heavy rains and rainy seasons are occurring in Korea. Periodic monitoring and rapid detection are important because these weather conditions can lead to drought and flooding, causing secondary damage. Although research using optical images is continuously being conducted to determine the waterbody, there is a limitation in that it is difficult to detect due to the influence of clouds in order to detect floods that accompany heavy rain. Therefore, there is a need for research using synthetic aperture radar (SAR) that can be observed regardless of day or night in all weather. In this study, using Sentinel-1 SAR images that can be collected in near-real time as open data, the UNet model among deep learning algorithms that have recently been used in various fields was applied. In previous studies, waterbody detection studies using SAR images and deep learning algorithms are being conducted, but only a small number of studies have been conducted in Korea. In this study, to determine the applicability of deep learning of SAR images, UNet and the existing algorithm thresholding method were compared, and five indices and Sentinel-2 normalized difference water index (NDWI) were evaluated. As a result of evaluating the accuracy with intersect of union (IoU), it was confirmed that UNet has high accuracy with 0.894 for UNet and 0.699 for threshold method. Through this study, the applicability of deep learning-based SAR images was confirmed, and if high-resolution SAR images and deep learning algorithms are applied, it is expected that periodic and accurate waterbody change detection will be possible in Korea.

• Journal of Korea Water Resources Association
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• v.49 no.12
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• pp.1027-1034
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• 2016

One of the most important purpose of multi-purpose reservoir is storing a large amount of water for utilization in a dry season. However, multi-purpose reservoirs that were constructed according to the limited hydrologic information available at the time of construction may encounter problems such as decreased water inflow due to climate change and an inability to cope with a water shortage. To solve these problems, in 2015, the Ministry of Land, Infrastructure and Transport suggested a revised water supply standard in case of water shortage for reservoirs. However, the revised standard has not been sufficiently discussed to determine its effectiveness. In addition, multi-purpose reservoirs in South Korea have secured and stored water for emergencies, but there is currently no way to utilize the stored water. Determining how to utilize the stored water effectively may be a useful method for preparing drought. Therefore, this article discusses the revised water supply standard as it relates to a water shortage in reservoirs and a method of utilizing the water stored for emergencies in multi-purpose reservoirs. The options for utilizing the water storage were evaluated using a water shortage safety degree index, and the results showed that the options may slightly and limitedly increase the water supply capacity. However, the evaluation also showed that a complex application of two options may overcome the exisiting problem and to supply water more effectively.

• Korean Journal of Remote Sensing
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• v.27 no.5
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• pp.601-611
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• 2011

Land cover changes are occurring for a variety of reasons such as urbanization, infrastructure construction, desertification, drought, flood, and so on. Many researchers have studied the cause and effect of land cover changes, and also the methods for change detection. However, most of the detection methods are based on the dichotomy of "change" and "not change" according a threshold value. In this paper, we present a change detection method with the integration of probability, spatial autocorrelation, and hotspot detection. We used the AMOEBA (A Multidirectional Ecotope-Based Algorithm) and developed the AMOEBA-CH (core hotspot) because the original algorithm tends to produce too many clusters. Our method considers the probability of land cover changes and the spatial interactions between each pixel and its neighboring pixels using a local spatial autocorrelation measure. The core hotspots of land cover changes can be delineated by a contiguity-dominance model of our AMOEBA-CH method. We tested our algorithm in a simulation for land cover changes using NDVI (Normalized Difference Vegetation Index) data in South Korea between 2000 and 2008.

• Journal of Korean Society of Forest Science
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• v.109 no.1
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• pp.31-40
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• 2020

This study aimed to investigate the effects of climate change on the survival and growth performance of Pinus densiflora and Larix kaempferi seedlings using open-field experimental warming and precipitation manipulation. We measured the survival rate, root-collar diameter, and height, and then calculated the seedling quality index (SQI) of 2-year-old seedlings under 6 treatments [2 temperatures (TC: Control; TW: Warming) × 3 precipitation manipulations (PC: Control; PD: Decreased; PI: Increased)] and performed a two-way ANOVA to test for differences.The air temperature of the warming plots was 3℃ higher than that of the control plots, while the precipitation manipulation plots received ±40% of the precipitation received by the control plots. Temperature and precipitation treatments did not significantly affect the survival rate of P. densiflora; however, the SQI of P. densiflora decreased with increasing precipitation. In contrast, the mortality rate of L. kaempferi increased with increasing temperature and decreasing precipitation. Furthermore, in L. kaempferi, TC × PI treatment resulted in the lowest SQI with a significant interaction effect observed between the two factors. In summary, low seedling production and quality should be expected in P. densiflora as precipitation increases and in L. kaempferi as temperature increases or precipitation decreases. These results indicate species-specific sensitivities to climate change of two plant species at the nursery stage. With the occurrence of global warming, the frequencies of drought and heavy rainfall events are increased, and this could affect the survival and seedling quality of tree species. Therefore, it is necessary to improve nursery techniques by establishing new adaptation strategies based on species-specific growth performance responses.

• Korean Journal of Environmental Biology
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• v.38 no.1
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• pp.30-39
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• 2020

The changes in fish stock and biomass before and after fishway renovation located in a Korean estuary were studied and fluctuations in the economic value of the fish resources were estimated. The target fishway located in the east coast area in Korea was renovated in 2014 from the small fish ladder to the ice-harbor fishway. Monitoring was continued for five consecutive years after the renovation(2015 to 2019). Since the renovation of the fish passage, the economic values increased with increases in the fishery resources, except for in 2016 when the drought impact was severe. The yearly average incremental increase in the five years after the renovation was about 227%. The increase in economic value is believed to be due to the increased population of migratory fish as a result of habitat expansion. The exponential rise model showed an increase in economic value with increasing fishery resources (R²=0.896). The model coefficient contributing to economic analysis was 0.582 and the maximum economic value after the renovation was estimated at about 30.4 million. The economic value would be a useful index for quantitative comparison in terms of ecosystem services before and after renovation.

• Korean Journal of Agricultural and Forest Meteorology
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• v.14 no.1
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• pp.28-38
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• 2012

This study was conducted to investigate growth performance, photosynthesis, water use efficiency (WUE), and stomatal conductance ($g_s$) of container seedlings of Liriodendron tulipifera and Zelkova serrata growing under three different irrigation periods (1 time/1 day, 1 time/2 days and 1 time/3 days) for high seedling quality. The root collar diameter and height of L. tulipifera and Z. serrata seedlings were highest with 1 time/1 day irrigation, whereas they were lowest with 1 time/3 days irrigation. The two species showed low drought tolerance. As irrigation period was shortened, biomass and seedling quality index (SQI) of the two species increased. The ratio of height to root collar diameter (H/D) and the ratio of below to aboveground biomass (T/R) of the two species were lower with 1 time/3 days than at other irrigation periods. L. tulipifera and Z. serrata seedlings showed significantly higher photosynthetic capacity with 1 time/1 day irrigation. As irrigation period was shortened, $g_s$ of two species increased, while their WUE decreased significantly (P<0.05) These results show that 1 time/1 day irrigation provides the most optimal water condition for container seedling production of two species and irrigation controlling is very important for growth and quality of container seedlings.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.391-391
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• 2018

가뭄은 일반적으로 강수량의 부족에 기인하며, 수자원의 이용 및 관리에 큰 영향을 미치는 자연재해이다. 2013년부터 2015년까지 우리나라의 연 평균 강수량은 각각 1,162mm, 1,173mm, 948mm로 평년대비 89.0%, 89.8%, 72.1%의 적은 강수를 보였다. 이는 마른장마, 평년보다 적게 발생한 태풍 등의 영향 인 것으로 판단되며 이러한 강수의 부족으로 인해 전국적으로 가뭄이 빈번하게 발생하였다. 이에 가뭄의 대처방안에 대한 관심이 증대되었고, 가뭄을 정량적으로 표현하고자 하는 연구들이 진행되었다. 가뭄은 크게 수문학적, 기상학적, 농업적 가뭄으로 구분되며 각각의 기준에 따라 다양한 변수들을 이용한 지표들이 개발되었다. 개발된 가뭄 지표는 가뭄을 평가하고 대비하기 위한 의사결정에 유용한 자료로 사용되고 있다. 농업적 가뭄은 강우부족, 실제와 잠재증발산량의 차이, 토양수분 부족, 저수지 또는 지하수위의 저하 등 농작물의 생육과 수확량에 직접적인 영향을 미치는 특성들을 고려하여 평가해야 하며, 이러한 특성들을 고려한 가뭄 지수로는 저수지 가뭄지수(RDI), 토양수분지수(SMI), 통합농업가뭄지수(IADI) 등이 개발되었다. 저수지 가뭄지수는 가뭄발생의 위험과 크기를 순별 가용저수량의 빈도를 이용하여 나타낸 가뭄 지표이다. 따라서 가뭄 지표를 산정하는데 사용된 자료의 기간에 따라 그 값의 차이가 존재한다. 본 연구에서는 각각 10개년, 20개년, 30개년 기간의 백산저수지 농업지구 저수량 자료를 사용하여 2011년부터 2015년까지의 저수지 가뭄지수를 산정하였으며 이를 각각 비교하였다. 2006년부터 2015년까지 10개년 기간의 자료를 사용하여 산정한 가뭄지수는 2012년 ~ 2015년에 가뭄을 나타내고 있었고 특히, 2015년 6월 상순과 중순의 가뭄지수가 -4.1으로 가장 심한 가뭄을 나타내었다. 1996년부터 2015년까지 20개년 기간의 자료를 사용하여 산정한 가뭄지수는 2012 ~ 2015년에 가뭄을 나타내며 2015년 6월 상순과 중순의 가뭄지수는 각각 -0.9, -1.0으로 10개년의 기간을 사용하였을 때보다 완화된 모습을 보였다. 1986년부터 2015년까지 30개년 기간의 자료를 사용하여 산정한 가뭄지수는 2011년부터 2015년까지 가뭄을 나타내고 있었으며, 2015년 6월 상순과 중순의 경우 각각 -1.7, -1.0으로 20개년 자료를 사용하였을 때보다 심한 가뭄을 나타내지만, 10개년 자료를 사용하였을 때보다 완화된 가뭄을 나타내었다. 백산저수지의 경우 2011년부터 2015년까지 가뭄이 발생하였으나, 용수공급이 불가능 할 정도의 가뭄이 발생하지는 않은 것으로 조사되었으며, 30개년 자료를 사용한 가뭄지수가 이와 가장 근사한 가뭄정도를 나타내고 있다.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.337-337
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• 2017

가뭄은 일반적으로 강수량의 부족에 기인하며, 수자원의 이용 및 관리에 큰 영향을 미치는 자연재해이다. 2013년부터 2015년까지 우리나라의 연 평균 강수량은 각각 1,162mm, 1,173mm, 948mm로 평년대비 89.0%, 89.8%, 72.1%의 적은 강수를 보였다. 이는 마른장마, 평년보다 적게 발생한 태풍 등의 영향 인 것으로 판단되며 이러한 강수의 부족으로 인해 전국적으로 가뭄이 빈번하게 발생하였다. 이에 가뭄의 대처방안에 대한 관심이 증대되었고, 가뭄을 정량적으로 표현하고자 하는 연구들이 진행되었다. 가뭄은 크게 수문학적, 기상학적, 농업적 가뭄으로 구분되며 각각의 기준에 따라 다양한 변수들을 이용한 지표들이 개발되었다. 개발된 가뭄 지표는 가뭄을 평가하고 대비하기 위한 의사결정에 유용한 자료로 사용되고 있다. 농업적 가뭄은 강우부족, 실제와 잠재증발산량의 차이, 토양수분 부족, 저수지 또는 지하수위의 저하 등 농작물의 생육과 수확량에 직접적인 영향을 미치는 특성들을 고려하여 평가해야 하며, 이러한 특성들을 고려한 가뭄 지수로는 저수지 가뭄지수(RDI), 토양수분지수(SMI), 통합농업가뭄지수(IADI) 등이 개발되었다. 저수지 가뭄지수는 가뭄발생의 위험과 크기를 순별 가용저수량의 빈도를 이용하여 나타낸 가뭄 지표이다. 따라서 가뭄 지표를 산정하는데 사용된 자료의 기간에 따라 그 값의 차이가 존재한다. 본 연구에서는 각각 10개년, 20개년, 30개년 기간의 백산저수지 농업지구 저수량 자료를 사용하여 2011년부터 2015년까지의 저수지 가뭄지수를 산정하였으며 이를 각각 비교하였다. 2006년부터 2015년까지 10개년 기간의 자료를 사용하여 산정한 가뭄지수는 2012년 ~ 2015년에 가뭄을 나타내고 있었고 특히, 2015년 6월 상순과 중순의 가뭄지수가 -4.1으로 가장 심한 가뭄을 나타내었다. 1996년부터 2015년까지 20개년 기간의 자료를 사용하여 산정한 가뭄지수는 2012 ~ 2015년에 가뭄을 나타내며 2015년 6월 상순과 중순의 가뭄지수는 각각 -0.9, -1.0으로 10개년의 기간을 사용하였을 때보다 완화된 모습을 보였다. 1986년부터 2015년까지 30개년 기간의 자료를 사용하여 산정한 가뭄지수는 2011년부터 2015년까지 가뭄을 나타내고 있었으며, 2015년 6월 상순과 중순의 경우 각각 -1.7, -1.0으로 20개년 자료를 사용하였을 때보다 심한 가뭄을 나타내지만, 10개년 자료를 사용하였을 때보다 완화된 가뭄을 나타내었다. 백산저수지의 경우 2011년부터 2015년까지 가뭄이 발생하였으나, 용수공급이 불가능 할 정도의 가뭄이 발생하지는 않은 것으로 조사되었으며, 30개년 자료를 사용한 가뭄지수가 이와 가장 근사한 가뭄정도를 나타내고 있다. 이는 저수량자료의 기간이 크면 빈도값의 신뢰성이 높아지기 때문인 것으로 판단되며 저수지 가뭄지수의 경우 저수량 자료가 누적될수록 좀 더 정확한 가뭄상황을 표현할 수 있을 것으로 판단된다.

• Journal of the Korean GEO-environmental Society
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• v.20 no.5
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• pp.5-12
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• 2019

On November 15, 2017, a unpredictable liquefaction damage was occurred at the $M_L=5.4$ Pohang earthquake and after, many researches have been conducted in Korea. In Korea, where there were no cases of earthquake damage, it has been extremely neglectable in preparing earthquake risk maps and building earthquake systems that corresponded to prevention and preparation. Since it is almost impossible to observe signs and symptoms of drought, floods, and typhoons in advance, it is very effective to predict the impacts and magnitudes of seismic events. In this study, 14,040 borehole data were collected in the metropolitan area and liquefaction evaluation was performed using the amplification factor. Based on this data, liquefaction hazard maps were prepared for ground accelerations of 0.06 g, 0.14 g, 0.22 g, and 0.30 g, including 200years return period to 4,800years return period. Also, the correlation analysis between the earthquake acceleration and LPI was carried out to draw a real-time predictable liquefaction hazard map. As a result, 707 correlation equations in every cells in GIS map were proposed. Finally, the simulation for liquefaction risk mapping against artificial earthquake was performed in the metropolitan area using the proposed correlation equations.