Korea Flux Monitoring Network (KoFlux) consists of about a dozen eddy covariance flux tower sites. Based on the carbon/water/energy fluxes between the biosphere and the atmosphere from KoFlux, we have been trying to identify trends and temporal scales of the variability in Korea. A necessary condition for such analyses is that the data from the network are comparable. One of the necessary conditions for the comparability of data is the compatibility of the sensors for measuring fluxes. Model CSAT3 (Campbell Scientific Inc.) of sonic anemometers have been employed almost all the sites of KoFlux, while various gas analyzers have been employed for each site (e.g., Models KH20, EC150, EC155, and IRGASON of Campbell Scientific Inc., Models LI-7500, LI-7500A, LI-7200, and LI-7200RS of LI-COR Inc.). It is well-known that the measured fluxes by the gas analyzers are considerably different, especially in low-flux environments. We had conducted the gas analyzer inter-comparison field experiment from August 2018 to March 2019 at a red pepper field in Yeoju, South Korea (37º 9' 58" N, 127º 40' 2" E) using the four open-path gas analyzers (i.e., Models EC150, IRGASON, LI-7500, LI-7500A) and the three closed-path gas analyzers (i.e., Models EC155, LI-7200, LI-7200RS). The purpose of this experiment is to ensure the compatibility of the gas analyzers in KoFlux.
Results/Conclusions
In this presentation, we will present the differences of CO2 and H2O fluxes among the sensors and discuss how we can minimize the differences in the post-processing procedure. It was preliminarily found that the CO2 flux measured by LI-7500 was negatively biased due to the instrument surface heating under the condition that the daily mean temperature was lower than 0°C. Despite applying the frequency response correction associated with tube attenuation of water vapor, the latent heat flux measured by EC155 was on average 9% smaller than that measured by LI-7500.
Acknowledgment This work was carried out with the support of "Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ014892022020)" Rural Development Administration, Republic of Korea. We are grateful to Taekyoung Chung and Kiwoon Kyung of B&P International Co. Ltd., and Sung-Won Choi, Juhan Park and Seungwon Sohn of National Center for AgroMeteorology, who helped to install the sensors for the field experiment. We specially thank Campbell Scientific Inc. and SOLDAN Inc. for giving us the loan of their instruments during the field experiment.