Ecology and Resilient Infrastructure

Korean Society of Ecology and Infrastructure Engineering (응용생태공학회)
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Development of a Method for Tracking Sandbar Formation by Weir-Gate Opening Using Multispectral Satellite Imagery in the Geumgang River, South Korea

금강에서 다분광 위성영상을 이용한 보 운영에 따른 모래톱 형성 추적 방법의 개발

  • Cheolho Lee (Department Biological Sciences and Bioengineering, Inha University) ;
  • Kang-Hyun Cho (Department of Biological Sciences, Inha University)
  • 이철호 (인하대학교 바이오시스템융합학부) ;
  • 조강현 (인하대학교 생명과학과)
  • Received : 2023.12.12
  • Accepted : 2023.12.14
  • Published : 2023.12.31
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Abstract

A various technology of remote sensing and image analysis are applied to study landscape changes and their influencing factors in stream corridors. We developed a method to detect landscape changes over time by calculating the optical index using multispectral images taken from satellites at various time points, calculating the threshold to delineate the boundaries of water bodies, and creating binarized maps into land and water areas. This method was applied to the upstream reach of the weirs in the Geumgang River to track changes in the sandbar formed by the opening of the weir gate. First, we collected multispectral images with a resolution of 10 m × 10 m taken from the Sentinel-2 satellite at various times before and after the opening of the dam in the Geumgang River. The normalized difference water index (NDWI) was calculated using the green light and near-infrared bands from the collected images. The Otsu's threshold of NDWI calculated to delineate the boundary of the water body ranged from -0.0573 to 0.1367. The boundary of the water area determined by remote sensing matched the boundary in the actual image. A map binarized into water and land areas was created using NDWI and the Otsu's threshold. According to these results of the developed method, it was estimated that a total of 379.7 ha of new sandbar was formed by opening the three weir floodgates from 2017 to 2021 in the longitudinal range from Baekje Weir to Daecheong Dam on the Geumgang River. The landscape detection method developed in this study is evaluated as a useful method that can obtain objective results with few resources over a wide spatial and temporal range.

하천 생태계에서 경관의 변화와 그 영향요인을 연구하기 위해 다양한 원격 탐지 및 영상 분석이 활용된다. 본 연구에서는 다양한 시점에서 위성에서 촬영된 다분광 영상으로 광학 지수를 계산하고, 수역의 경계를 획정하는 임계치를 계산하여 육역과 수역으로 이진화한 지도를 작성하여 시간에 따른 경관 변화를 탐지하는 방법을 개발하였다. 그리고 이 방법을 금강에 적용하여 보 수문 개방에 의하여 형성된 모래톱의 변화를 추적하였다. 먼저 금강에서 보 개방 전후의 다양한 시점에서 Sentinel-2 위성에서 촬영된 10 m × 10 m 해상도의 다분광 영상을 수집하였다. 수집된 영상에서 녹색광과 근적외선 대역으로 정규수분지수 (normalized difference water index, NDWI)를 계산하였다. 수역의 경계를 결정하기 위하여 산출한 NDWI의 Otsu 임계값은 -0.0573부터 0.1367의 범위이었다. 원격탐사에 의하여 결정된 수역의 경계는 실제 영상에서의 경계와 일치하였다. 이 NDWI에 의하여 수역과 육역으로 이진화된 지도를 작성하였다. 이 결과에 따르면 금강의 백제보부터 대청댐까지 종적 범위에서 2017년부터 2021년까지 수행된 3개의 보 수문 개방에 의해 총 379.7 ha의 새로운 모래톱의 서식처가 형성된 것으로 추정되었다. 본 연구에서 제안하는 경관 탐지 방법은 넓은 시공간 범위에서 적은 자원으로도 객관적인 결과를 얻을 수 있는 방법으로 평가된다.

Keywords

Acknowledgement

본 결과물은 환경부의 재원으로 한국환경산업기술원 수생태계 건강성 확보 기술개발사업의 지원을 받아 연구되었습니다 (2020003050002).

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