KSCE Journal of Civil and Environmental Engineering Research (대한토목학회논문집)

Korean Society of Civil Engeneers (대한토목학회)
권호 표지

Improvement of Water Area Classification During a Flood Using RADARSAT SAR Imagery and Terrain Informations In Mountainous Area

RADARSAT SAR 영상과 지형정보를 이용한 홍수시 산악지역의 수계영역 추출 정확도 향상

Sohn, Hong-Gyoo;Song, Yeong-Sun;Chang, Hoon
손홍규;송영선;장훈

  • Published : 2004.03.31

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Abstract

The brightness values of Synthetic Aperture Radar (SAR) imagery are largely influenced by the local terrain relief. In water areas such as oceans and rivers with relatively flat areas, SAR imagery has lower backscattered signals than other surfaces. Although SAR imagery with its own energy sources is very applicable to flood monitoring due to its sensitivity to the water area, several distortions caused by local terrain relief must be carefully considered before actual classification process. Since backscattering coefficients of shadow area are very similar to those of the water area, it is essential to remove the radiometric distortion caused by local relief especially in mountainous areas. In this study we tested four different cases of local terrain relief compensation processes based on the preprocessing of input SAR imagery and local surface information such as elevation and slopes for accurate water extent. The case when the input RADARSAT SAR imagery is classified with the local slope information is best in terms of flood area estimation, even in small streams and watershed of different elevation categories. Consequently in mountainous areas the combination of SAR imagery and slope information is the best combination in the estimation of inundated areas during the flood.

SAR영상의 밝기값은 지형의 기복에 영향을 받는다. 특히, 하천이나 강과 같은 수계지역에 대해서는 돌아오는 역산란 에너지가 적기 때문에 SAR 영상은 광학영상에 비해서 수계지역이 뚜렷하게 나타나는 반면지형의 기복에 따라 여러 가지 복잡한 왜곡현상이 발생한다. 지형의 기복에 의한 지형효과왜곡이 발생하는 지역은 수계지역과 비슷한 반사특성(낮은 dB값)을 보임으로서 수계지역 분류 시 많은 오류를 발생시킨다. 따라서 일반적으로 대상지역이 평지인 경우 기본적인 방사보정만을 수행하더라도 정확한 수계지역을 분류해 낼 수 있지만 산악지역으로 구성된 경우, 방사보정 외에 지형효과왜곡을 보정해야 하는 등의 복잡한 과정을 거쳐야 한다. 본 연구에서는 RADARSAT 영상으로부터 수계지역의 분류를 위해 방사보정, 지형효과 왜곡 보정, 고도자료 및 경사도 자료를 이용하여 수계영역을 추출을 수행하였다. 그 결과 RADARSAT SAR영상만을 활용할 경우 추출 정확도에 한계를 보였으며, RADARSAT SAR 영상에 지형정보를 추가로 활용함으로서 정확한 수계영역을 추출할 수 있었다. 특히 SAR영상과 경사도 자료를 동시에 활용하여 산악지역의 수계지역을 추출하는 것이 가장 효과적임을 알 수 있었다.

Keywords

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