Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography (한국측량학회지)

Korean Society of Surveying, Geodesy, Photogrammetry and Cartography (한국측량학회)
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Evaluation of Rededge-M Camera for Water Color Observation after Image Preprocessing

영상 전처리 수행을 통한 Rededge-M 카메라의 수색 관측에의 활용성 검토

  • Kim, Wonkook (Dept. Civil and Environmental Engineering, Pusan National University) ;
  • Roh, Sang-Hyun (REDONE TECHNOLOGIES Co. Ltd.) ;
  • Moon, Yongseon (Dept. Electric Engineering, Sunchon National University) ;
  • Jung, Sunghun (Department of Electric Vehicle Engineering, Dongshin University)
  • Received : 2019.05.30
  • Accepted : 2019.06.26
  • Published : 2019.06.30
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Abstract

Water color analysis allows non-destructive estimation of abundance of optically active water constituents in the water body. Recently, there have been increasing needs for light-weighted multispectral cameras that can be integrated with low altitude unmanned platforms such as drones, autonomous vehicles, and heli-kites, for the water color analysis by spectroradiometers. This study performs the preprocessing of the Micasense Rededge-M camera which recently receives a growing attention from the earth observation community for its handiness and applicability for local environment monitoring, and investigates the applicability of Rededge-M data for water color analysis. The Vignette correction and the band alignment were conducted for the radiometric image data from Rededge-M, and the sky, water, and solar radiation essential for the water color analysis, and the resultant remote sensing reflectance were validated with an independent hyperspectral instrument, TriOS RAMSES. The experiment shows that Rededge-M generally satisfies the basic performance criteria for water color analysis, although noticeable differences are observed in the blue (475 nm) and the near-infrared (840 nm) band compared with RAMSES.

물의 색깔 즉, 수색(水色)을 분석하면 그 물이 함유하고 있는 유색 구성물질의 분포 및 농도를 비파괴적으로 추정할 수 있다. 이러한 분석을 위해 분광복사계를 사용하는데, 최근 드론, 자율운행차, 헬리카이트 등의 저고도 무인 플랫폼에 장착하기 위한 경량 다분광 카메라에 대한 수요가 높아지고 있다. 본 연구에서는 최근 활용 용이성으로 인해 지역적 환경 변화를 모니터링함에 있어 그 활용도가 높아진 Micasense사의 Rededge-M 다분광 카메라의 전처리를 수행하고, 수색관측에의 활용성을 검증하기 위한 분석을 수행하였다. 우선, 영상 형태로 생성되는 자료에서의 Vignette 보정 및 밴드 정렬을 수행하였고, 수색관측을 위해 필요한 하늘, 물, 태양광을 측정한 복사량 그리고 그로부터 최종적으로 도출되는 원격탐사 반사도 관측치를 독립적인 초분광 센서의 관측값과 비교하여 분석하였다. 실험 결과, 전처리 과정을 수행하였을 시, 청색밴드(475 nm)와 근적외선 밴드(840 nm)에서 주목할 만한 차이가 있었지만, Rededge-M은 전반적으로 수색 분석을 위한 기본적인 광학적 성능을 가지고 있음을 확인하였다.

Keywords

GCRHBD_2019_v37n3_167_f0001.png 이미지

Fig. 2. (a) The package that contains the reference panel and the QR code which directs users to the reflectance information of the panel, and (b) the Rededge-M image with the panel and the QR code portions detected automatically

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Fig. 5. (a) Correction factor of Vignette model derived for the 5 spectral bands for sky radiance(Lsky), and (b) sky radiance after the radiometric correction including the Vignette correction

GCRHBD_2019_v37n3_167_f0003.png 이미지

Fig. 7. Spectrum for (a) total water radiance(Lw), (b) sky radiance(Lsky), (c) downward solar irradiance (Ed), and (d) remote sensing reflectance(Rrs)

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Fig. 8. Spectrum obtained by Rededge-M camera and RAMSES sensor for (a) total water radiance(Lw), (b) sky radiance(Lsky), (c) downward solar irradiance (Ed), and (d) remote sensing reflectance(Rrs)

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Fig. 1. (a) Rededge-M camera with the DLS sensor and the GPS module, (b) Aperture alignment for the 5 spectral bands

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Fig. 3. Location of two observation stations: (a) the seashore of Youngdo island in Pusan, and (b) the seashore of Tongyoung

GCRHBD_2019_v37n3_167_f0007.png 이미지

Fig. 4. (a) Correction factor of Vignette model derived for the 5 spectral bands for total water radiance( Lw), and (b) total water radiance after the radiometric correction including the Vignette correction

GCRHBD_2019_v37n3_167_f0008.png 이미지

Fig. 6. RGB composite images for (a) horizontal view, (c) water, and (e) sky before the band alignment, and the images after the band alignment for (b) horizontal view, (d) water, and (f) sky

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