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Determination of dynamic threshold for sea-ice detection through relationship between 11 µm brightness temperature and 11-12 µm brightness temperature difference

11 µm 휘도온도와 11-12 µm 휘도온도차의 상관성 분석을 활용한 해빙탐지 동적임계치 결정

  • Jin, Donghyun (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University) ;
  • Lee, Kyeong-Sang (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University) ;
  • Choi, Sungwon (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University) ;
  • Seo, Minji (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University) ;
  • Lee, Darae (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University) ;
  • Kwon, Chaeyoung (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University) ;
  • Kim, Honghee (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University) ;
  • Lee, Eunkyung (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University) ;
  • Han, Kyung-Soo (Division of Earth Environmental System Science(Major of Spatial Information Engineering), Pukyong National University)
  • 진동현 (부경대학교 지구환경시스템과학부 공간정보시스템공학과) ;
  • 이경상 (부경대학교 지구환경시스템과학부 공간정보시스템공학과) ;
  • 최성원 (부경대학교 지구환경시스템과학부 공간정보시스템공학과) ;
  • 서민지 (부경대학교 지구환경시스템과학부 공간정보시스템공학과) ;
  • 이다래 (부경대학교 지구환경시스템과학부 공간정보시스템공학과) ;
  • 권채영 (부경대학교 지구환경시스템과학부 공간정보시스템공학과) ;
  • 김홍희 (부경대학교 지구환경시스템과학부 공간정보시스템공학과) ;
  • 이은경 (부경대학교 지구환경시스템과학부 공간정보시스템공학과) ;
  • 한경수 (부경대학교 지구환경시스템과학부 공간정보시스템공학과)
  • Received : 2017.03.22
  • Accepted : 2017.03.27
  • Published : 2017.04.30

Abstract

Sea ice which is an important component of the global climate system is being actively detected by satellite because it have been distributed to polar and high-latitude region. and the sea ice detection method using satellite uses reflectance and temperature data. the sea ice detection method of Moderate-Resolution Imaging Spectroradiometer (MODIS), which is a technique utilizing Ice Surface Temperature (IST) have been utilized by many studies. In this study, we propose a simple and effective method of sea ice detection using the dynamic threshold technique with no IST calculation process. In order to specify the dynamic threshold, pixels with freezing point of MODIS IST of 273.0 K or less were extracted. For the extracted pixels, we analyzed the relationship between MODIS IST, MODIS $11{\mu}m$ channel brightness temperature($T_{11{\mu}m}$) and Brightness Temperature Difference ($BTD:T_{11{\mu}m}-T_{12{\mu}m}$). As a result of the analysis, the relationship between the three values showed a linear characteristic and the threshold value was designated by using this. In the case ofsea ice detection, if $T_{11{\mu}m}$ is below the specified threshold value, it is detected as sea ice on clear sky. And in order to estimate the performance of the proposed sea ice detection method, the accuracy was analyzed using MODIS Sea ice extent and then validation accuracy was higher than 99% in Producer Accuracy (PA).

지구 기후시스템의 중요구성인자인 해빙은 극지방과 고위도에 분포하는 특성상 위성을 통한 탐지가 활발히 수행되고 있다. 위성자료를 이용한 해빙탐지기법은 반사도와 휘도온도자료를 이용하며, 많은 연구에서 휘도온도자료를 통해 산출된 Ice Surface Temperature (IST)를 활용한 기법인 Moderate-Resolution Imaging Spectroradiometer (MODIS)의 해빙탐지기법을 활용하고 있다. 본 연구에서는 IST 산출과정이 생략된 단순하고 효율적인 동적임계값 기법을 활용한 해빙탐지기법을 제시하고자 한다. 동적임계값을 지정하기 위하여 해수의 어는점 이하의 화소를 대상으로 MODIS IST와 MODIS $11{\mu}m$ 채널의 휘도온도, Brightness Temperature Difference ($BTD:T_{11{\mu}m}-T_{12{\mu}m}$)의 상호관계를 분석하였다. 분석 결과, 세수치의 관계가 선형의 특징을 나타내었으며 이를 활용하여 임계값을 지정하였다. 청천역에서 지정한 임계값을 MODIS $11{\mu}m$ 채널에 적용하여 해빙을 탐지하였다. 또한, 본 연구의 해빙탐지기법의 성능을 검증하기 위해 MODIS Sea ice extent를 이용하여 정확도를 분석하였으며 그 결과, Producer Accuracy (PA) 99% 이상의 높은 정확도를 보였다.

Keywords

References

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