Korean Journal of Agricultural and Forest Meteorology (한국농림기상학회지)

Korean Society of Agricultural and Forest Meteorology (한국농림기상학회)
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Corrections on CH4 Fluxes Measured in a Rice Paddy by Eddy Covariance Method with an Open-path Wavelength Modulation Spectroscopy

개회로 파장 변조 분광법과 에디 공분산 방법으로 논에서 관측된 CH4 플럭스 자료의 보정

  • Kang, Namgoo (Korea research Institute of Standards and Science) ;
  • Yun, Juyeol (Complex Systems Science Lab., Department of Landscape Architecture and Rural Systems Engineering, Seoul National University) ;
  • Talucder, M.S.A. (Interdisciplinary Program in Agricultural & Forest Meteorology, Seoul National University) ;
  • Moon, Minkyu (National Center for AgroMeteorology) ;
  • Kang, Minseok (National Center for AgroMeteorology) ;
  • Shim, Kyo-Moon (National Academy of Agricultural Science) ;
  • Kim, Joon (Complex Systems Science Lab., Department of Landscape Architecture and Rural Systems Engineering, Seoul National University)
  • Received : 2014.10.28
  • Accepted : 2014.12.01
  • Published : 2015.03.30
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Abstract

$CH_4$ is a trace gas and one of the key greenhouse gases, which requires continuous and systematic monitoring. The application of eddy covariance technique for $CH_4$ flux measurement requires a fast-response, laser-based spectroscopy. The eddy covariance measurements have been used to monitor $CO_2$ fluxes and their data processing procedures have been standardized and well documented. However, such processes for $CH_4$ fluxes are still lacking. In this note, we report the first measurement of $CH_4$ flux in a rice paddy by employing the eddy covariance technique with a recently commercialized wavelength modulation spectroscopy. $CH_4$ fluxes were measured for five consecutive days before and after the rice transplanting at the Gimje flux monitoring site in 2012. The commercially available $EddyPro^{TM}$ program was used to process these data, following the KoFlux protocol for data-processing. In this process, we quantified and documented the effects of three key corrections: (1) frequency response correction, (2) air density correction, and (3) spectroscopic correction. The effects of these corrections were different between daytime and nighttime, and their magnitudes were greater with larger $CH_4$ fluxes. Overall, the magnitude of $CH_4$ flux increased on average by 20-25% after the corrections. The National Center for AgroMeteorology (www.ncam.kr) will soon release an updated KoFlux program to public users, which includes the spectroscopic correction and the gap-filling of $CH_4$ flux.

$CH_4$는 $CO_2$ 및 $N_2O$와 더불어 중요한 온실가스로서 지속적이고도 체계적인 감시가 요구된다. 에디 공분산 기술 기반의 $CO_2$ 플럭스의 관측은 이미 세계적으로 관측망이 구축되어 관측부터 자료처리에 이르기까지 모든 과정이 표준화되어 있을 뿐 아니라 체계적으로 잘 문서화되어 있다. 그러나 미량 기체인 $CH_4$의 경우, 레이저 기반의 고속반응 분광계를 필요로 할 뿐 아니라, 이에 수반되는 플럭스 자료의 처리 과정이 표준화되어 있지 않다. 본 연구 노트에서는 최근에 상용화된 개회로 파장 변조 분광계를 사용하여 에디 공분산 방법으로 논에서 관측한 $CH_4$ 플럭스 결과를 보고하였다. 모내기 전과 직후의 각 5일간 연속 관측한 자료를 KoFlux 프로토콜에 따라 상용화된 $EddyPro^{TM}$ 프로그램을 사용하여 자료를 처리하였다. 이 후처리 과정에서 세 가지 주요 보정, (1) 주파수 반응 보정, (2) 공기 밀도 보정, (3) 분광 보정의 효과를 정량화 하였다. 보정 효과는 밤과 낮에 따라 차이를 보였고, 메탄플럭스가 작을수록 보정 효과가 컸다. 전반적으로 보정 후에 메탄 플럭스는 평균 20-25% 정도 증가하였다. 국가농림기상센터(www.ncam.kr)에서는 분광 보정과 빈 자료 메우기를 포함한 $CH_4$플럭스 자료 처리가 포함된 업데이트된 KoFlux 프로그램을 일반 사용자에게 제공할 예정이다.

Keywords

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  2. Interannual variations in methane emission from an irrigated rice paddy caused by rainfalls during the aeration period vol.223, 2016, https://doi.org/10.1016/j.agee.2016.02.032
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