• Journal of Environmental Science International
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• v.31 no.9
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• pp.735-741
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• 2022

Global warming affects forests and their ecology. Diversity in the forest is a buffer that reduces the damage due to global warming. Mixed forests are ecologically more valuable as versatile habitats and are effective in preventing landslides. In Korea, most forests were created by simple afforestation with trees of evergreen species. Typically, evergreen trees are shallow-rooted, and deciduous trees are deep-rooted. Mixed forest tree roots grip the soil effectively, which reduces the occurrence of landslides. Therefore, improving the distribution of tree types is essential to reduce damage due to global warming. For this improvement, the investigation of tree types of the forest is needed. However, determining the tree type distribution of forests that are spread over wide areas is labor-intensive and time-consuming. This study suggests effective methods for determining the distribution of tree types in a forest that is spread across a relatively wide area. Using normalized difference vegetation index and RGB images from unmanned aerial vehicles, each evergreen and deciduous tree, and grassland area can be distinguished. The distinguished image determines the distribution of tree type. This method is effective compared to directly determining the tree type distribution in the forest by the use of manpower. The data from these methods could be applied to plan a mixed forest or to prepare for future damage due to global warming.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.3-3
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• 2023

수자원위성은 C-band 영상레이더(synthetic aperture radar, SAR)를 탑재한 중형급의 수자원 관리 및 수재해 감시 전용 위성이다. 수자원위성은 물 환경과 관련된 다양한 분야에 활용되어 고부가가치의 정보를 제공할 것으로 예상되는데, 특히 시계열 레이더 간섭기법(SAR interferometry, InSAR)의 적용을 통해 댐·보와 같은 수자원시설물의 미세변위 탐지 및 안정성 평가에 효과적으로 사용될 것으로 기대된다. 시계열 영상레이더 간섭기법은 고정산란체를 이용하는 Persistent Scatterer InSAR(PSInSAR) 기법과 분산산란체 기반의 Small BAseline Subset(SBAS) InSAR 기법으로 대표된다. 이 연구에서는 수자원위성에 적합한 수리시설물 시계열 변위 모니터링 알고리즘 개발을 목적으로, Sentinel-1 위성의 C-band SAR 기반 시계열 레이더 간섭기법의 적용성을 평가하고 알고리즘 개발에 고려해야 할 사항들을 분석하였다. 2020년 여름 수재해가 발생한 섬진강댐과 담양댐 및 수변부를 테스트 사이트로 선정하고, 2019년부터 2021년까지의 Sentinel-1 시계열 SAR 영상에 PSInSAR와 SBAS InSAR를 적용하여 시계열 변위를 관측하였다. 댐체에서는 PSInSAR가 SBAS InSAR에 비해 신뢰할 수 있는 시계열 변위를 산출하였다. 그러나 시계열 분석 기간이 길어짐에 따라 PSInSAR 시계열 변위의 정밀도가 낮아지는 경향이 관측되었다. 수변부에서 PSInSAR는 변위 정보를 거의 제공하지 못했다. SBAS InSAR는 수변부의 시계열 변위 모니터링에 효과적이었으나, 여름철 장마 등으로 인해 레이더 간섭도의 긴밀도(coherence)가 낮아질 경우 부정확한 변위를 산출하였다. 앞으로 국내의 다양한 수자원시설물을 대상으로 Sentinel-1 위성을 이용한 시계열 변위 모니터링 알고리즘의 적용성 평가 연구가 진행될 예정이며, 연구 결과를 수자원위성의 관측 특성에 적합한 변위 탐지 알고리즘의 개발에 활용하고자 한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.118-118
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• 2021

최근 지구 온난화 현상으로 인한 기후변화로 이상기후 현상이 발생하고 있으며 이로 인해 장기적으로 폭염의 빈도 및 강도 상승에 따른 가뭄 피해 우려가 증가하고 있다. 농업 가뭄은 강수량 부족, 토양 수분 부족, 저수량 부족 등 농업분야에 영향을 주는 인자들과 관련되어 있어 농작물 생육 및 수확량 감소를 야기한다. 우리나라는 논농사가 주를 이루고 있어 국내 농업 가뭄은 주수원공인 농업용 저수지의 가용저수용량으로 판단 가능하다. 따라서 안정적인 농업용수 공급을 위해 수리시설물의 모니터링, 공급량 등의 분석이 이루어져야 하며, 농업 가뭄에 대비하기 위해 농업용 저수지의 가용저수용량 파악이 필요하다. 수자원 분야에서 지점자료의 시·공간적 한계점을 보완하기 위해 인공위성 자료를 활용한 연구가 활발히 이루어지고 있으며, 본 연구에서는 위성영상 자료 및 딥러닝 기반 알고리즘을 적용하여 농업용 저수지 수표면 탐지 및 시계열 분석을 목적으로 한다. 위성영상 자료는 5일 주기 및 10 m 공간해상도를 가진 Sentinel-2 위성영상 자료를 활용하고자 하였으며, 딥러닝에 적용하기 위하여 100장 이상의 영상 이미지를 구축하였다. 딥러닝 기반 알고리즘으로는 Convolutional Neural Network (CNN)을 활용하였으며, CNN은 주로 이미지 분류나 객체 검출 문제를 해결하기 위해 제안된 모델로 최근 픽셀 단위로 분류가 가능한 알고리즘이 개발되어 높은 정확도의 수표면 탐지가 가능할 것으로 판단된다. 따라서 본 연구에서는 CNN 기반 수표면 탐지 알고리즘을 개발하여 Sentinel-2 영상 기준 경기도 안성시를 대상으로 소규모 농업용 저수지의 수표면적에 대한 시계열 데이터를 분석하고자 한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.27-27
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• 2022

본 연구는 본 연구에서는 내륙에 위치한 하천(백제보)과 호소(남양호)를 대상으로 수체반사도를 활용하여 유역특성에 따른 반사도의 변화를 확인하고 Chlorophyll-a(Chl-a)의 농도를 추정하고자 하였다. 각 유역별 특성분석을 위해 제원자료, 토지피복도 및 11개(수소이온농도, 용존산소, BOD, COD, 부유물질, 총질소, 총인, 수온, 전기전도도 및 Chlorophyll-a)의 수질인자 자료를 구축하였다. 백제보는 2016-2017년 유인항공기에 탑재된 초분광센서를 이용하여 반사도를 측정하였고, 남양호는 2020-2021년 초분광센서가 탑재된 Drone과 Sentinel-2 MSI영상으로부터 반사도를 측정하였으며 두 유역 모두 촬영 범위에 대하여 현장샘플링을 실시하였다. 유역특성, 수질인자간 상관성 및 밴드별 상관성 분석을 실시하였다. 수질인자 간 상관성 분석 결과 Chl-a와 광학적 특징이 있는 SS, TOC가 상관성이 높게 나타났으며, 반사도의 경우 Chl-a가 고농도일수록 Near-Infrared, Blue 파장과 상관성이 높게 나타났다. 해당 분석결과를 기반으로 각 유역에 대해 Chl-a Machine-learning 기법과 원격탐사자료를 이용하여 Chl-a의 농도를 산정하였으며 백제보, 남양호 각각 결정계수(R²) 0.80, 0.88의 성능을 보였다. 추후 고해상도 광학위성영상을 통해 유역특성을 고려한 광범위한 지역 규모의 Chl-a의 시공간적 분석이 가능할 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.329-329
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• 2022

Accurate characterization of terrestrial precipitation variation from high spatial resolution satellite sensors is beneficial for urban hydrology and microscale agriculture modeling, as well as natural disasters (e.g., urban flooding) early warning. However, the widely-used top-down approach for precipitation retrieval from microwave satellites is limited in several hydrological and agricultural applications due to their coarse spatial resolution. In this research, we aim to apply a novel bottom-up method, the parameterized SM2RAIN, where precipitation can be estimated from soil moisture signals based on an inversion of water balance model, to generate high spatial resolution terrestrial precipitation estimates at 0.01º grid (roughly 1-km) from the C-band SAR Sentinel-1. This product was then tested against a common reanalysis-based precipitation data and a domestic rain gauge network from the Korean Meteorological Administration (KMA) over central South Korea, since a clear difference between climatic types (coasts and mainlands) and land covers (croplands and mixed forests) was reported in this area. The results showed that seasonal precipitation variability strongly affected the SM2RAIN performances, and the product derived from separated parameters (rainy and non-rainy seasons) outperformed that estimated considering the entire year. In addition, the product retrieved over the mainland mixed forest region showed slightly superior performance compared to that over the coastal cropland region, suggesting that the 6-day time resolution of S1 data is suitable for capturing the stable precipitation pattern in mainland mixed forests rather than the highly variable precipitation pattern in coastal croplands. Future studies suggest comparing this product to the traditional top-down products, as well as evaluating their integration for enhancing high spatial resolution precipitation over entire South Korea.

• Nuclear Medicine and Molecular Imaging
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• v.41 no.4
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• pp.309-316
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• 2007

Purpose: Sentinel lymph node biopsy became the standard procedure in early breast cancer surgery. Faculty members might be exposed to a trace amount of radiation. The aim of this study is to quantify the radiation exposure and verify the safety of the procedure and the facilities, especially during pathologic process. Materials and Methods: Sentinel lymph node biopsies with Tc-99m human serum albumin were performed as routine clinical work. Exposed radiation doses were measured in pathologic technologist, nuclear medicine technologist, and nuclear medicine physician using a thermoluminescence dosimeter (TLD) during one month. We also measured the residual radioactivities or absorbed dose rates, the exposure distance and time during procedure, the radiation dose of the waste and the ambient equivalent dose of the pathology laboratory. Results: Actual exposed doses were 0.21 and 0.85 (uSv/study) for the whole body and hand of pathology technologist after 47 sentinel node pathologic preparations were performed. Whole body exposed doses of nuclear medicine physician and technologist were 0.2 and 2.3 (uSv/study). According to this data and the exposure threshold of the general population (1 mSv), at least 1100 studies were allowed in pathology technologist. The calculated exposed dose rates (${\mu}$ Sv/study) from residual radioactivities data were 2.47/ 22.4 ${\mu}$ Sv (whole body/hand) for the surgeon; 0.22/ 0 ${\mu}$ Sv for operation nurse. The ambient equivalent dose of the pathology laboratory was 0.02-0.03 mR/hr. The radiation dose of the waste was less than 100 Bq/g and nearly was not detected. Conclusion: Pathologic procedure relating sentinel lymph node biopsy using radioactive colloid is safe in terms of the radiation safety.(Nucl Med Mol Imaging 2007;41(4);309-316)

• Korean Journal of Remote Sensing
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• v.37 no.5_2
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• pp.1329-1340
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• 2021

The intertidal zone, which is a transitional zone between the ocean and the land, requires continuous monitoring as various changes occur rapidly due to artificial activity and natural disturbance. Monitoring of coastal topography changes using remote sensing method is evaluated to be effective in overcoming the limitations of intertidal zone accessibility and observing long-term topographic changes in intertidal zone. Most of the existing coastal topographic monitoring studies using remote sensing were conducted through high spatial resolution images such as Landsat and Sentinel. This study extracted the waterline using the NDWI from the GOCI-II (Geostationary Ocean Color Satellite-II) data, identified the changes in the intertidal area in Gyeonggi Bay according to various tidal heights, and examined the utility of DEM generation and topography altitude change observation over a short period of time. GOCI-II (249 scenes), Sentinel-2A/B (39 scenes), Landsat 8 OLI (7 scenes) images were obtained around Gyeonggi Bay from October 8, 2020 to August 16, 2021. If generating intertidal area DEM, Sentinel and Landsat images required at least 3 months to 1 year of data collection, but the GOCI-II satellite was able to generate intertidal area DEM in Gyeonggi Bay using only one day of data according to tidal heights, and the topography altitude was also observed through exposure frequency. When observing coastal topography changes using the GOCI-II satellite, it would be a good idea to detect topography changes early through a short cycle and to accurately interpolate and utilize insufficient spatial resolutions using multi-remote sensing data of high resolution. Based on the above results, it is expected that it will be possible to quickly provide information necessary for the latest topographic map and coastal management of the Korean Peninsula by expanding the research area and developing technologies that can be automatically analyzed and detected.

• Korean Journal of Remote Sensing
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• v.37 no.5_1
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• pp.1029-1042
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• 2021

As part of the next-generation Compact Advanced Satellite 500 (CAS500) project, CAS500-4 is scheduled to be launched in 2025 focusing on the remote sensing of agriculture and forestry. To obtain quantitative information on vegetation from satellite images, it is necessary to acquire surface reflectance through atmospheric correction. Thus, it is essential to develop an atmospheric correction method suitable for CAS500-4. Since the absorption and scattering characteristics in the atmosphere vary depending on the wavelength, it is needed to analyze the sensitivity of atmospheric correction parameters such as aerosol optical depth (AOD) and water vapor (WV) considering the wavelengths of CAS500-4. In addition, as CAS500-4 has only five channels (blue, green, red, red edge, and near-infrared), making it difficult to directly calculate key parameters for atmospheric correction, external parameter data should be used. Therefore, thisstudy performed a sensitivity analysis of the key parameters (AOD, WV, and O₃) using the simulated images based on Sentinel-2 satellite data, which has similar wavelength specifications to CAS500-4, and examined the possibility of using the products of GEO-KOMPSAT-2A (GK2A) as atmospheric parameters. The sensitivity analysisshowed that AOD wasthe most important parameter with greater sensitivity in visible channels than in the near-infrared region. In particular, since AOD change of 20% causes about a 100% error rate in the blue channel surface reflectance in forests, a highly reliable AOD is needed to obtain accurate surface reflectance. The atmospherically corrected surface reflectance based on the GK2A AOD and WV was compared with the Sentinel-2 L2A reflectance data through the separability index of the known land cover pixels. The result showed that two corrected surface reflectance had similar Seperability index (SI) values, the atmospheric corrected surface reflectance based on the GK2A AOD showed higher SI than the Sentinel-2 L2A reflectance data in short-wavelength channels. Thus, it is judged that the parameters provided by GK2A can be fully utilized for atmospheric correction of the CAS500-4. The research findings will provide a basis for atmospheric correction of the CAS500-4 in the future.

• Korean Journal of Remote Sensing
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• v.37 no.6_1
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• pp.1773-1784
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• 2021

In order to minimize damage to oil spill accidents in the ocean, it is essential to collect a spilled area as soon as possible. Thus satellite-based remote sensing is a powerful source to detect oil spills in the ocean. With the recent rapid increase in the number of available satellites, it has become possible to generate a status report of marine oil spills soon after the accident. In this study, the oil spill area was calculated using various satellite images for the Symphony oil spill accident that occurred off the coast of Qingdao Port, China, on April 27, 2021. In particular, improving the accuracy of oil spill area determination was applied using high-resolution commercial satellite images with a spatial resolution of 2m. Sentinel-1, Sentinel-2, LANDSAT-8, GEO-KOMPSAT-2B (GOCI-II) and Skysat satellite images were collected from April 27 to May 13, but five images were available considering the weather conditions. The spilled oil had spread northeastward, bound for coastal region of China. This trend was confirmed in the Skysat image and also similar to the movement prediction of oil particles from the accident location. From this result, the look-alike patch observed in the north area from the Sentinel-1A (2021.05.01) image was discriminated as a false alarm. Through the survey period, the spilled oil area tends to increase linearly after the accident. This study showed that high-resolution optical satellites can be used to calculate more accurately the distribution area of spilled oil and contribute to establishing efficient response strategies for oil spill accidents.

• Korean Journal of Remote Sensing
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• v.37 no.3
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• pp.543-557
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• 2021

Because aerosols have different spectral characteristics according to the size and composition of the particle and to the satellite sensors, a comparative analysis of aerosol products from various satellite sensors is required. In South Korea, however, a comprehensive study for the comparison of various official satellite AOD (Aerosol Optical Depth) products for a long period is not easily found. In this paper, we aimed to assess the performance of the AOD products from MODIS (Moderate Resolution Imaging Spectroradiometer), VIIRS (Visible Infrared Imaging Radiometer Suite), Himawari-8, and Sentinel-3 by referring to the AERONET (Aerosol Robotic Network) sun photometer observations for the period between January 2015 and December 2019. Seasonal and geographical characteristics of the accuracy of satellite AOD were also analyzed. The MODIS products, which were accumulated for a long time and optimized by the new MAIAC (Multiangle Implementation of Atmospheric Correction) algorithm, showed the best accuracy (CC=0.836) and were followed by the products from VIIRS and Himawari-8. On the other hand, Sentinel-3 AOD did not appear to have a good quality because it was recently launched and not sufficiently optimized yet, according to ESA (European Space Agency). The AOD of MODIS, VIIRS, and Himawari-8 did not show a significant difference in accuracy according to season and to urban vs. non-urban regions, but the mixed pixel problem was partly found in a few coastal regions. Because AOD is an essential component for atmospheric correction, the result of this study can be a reference to the future work for the atmospheric correction for the Korean CAS (Compact Advanced Satellite) series.