On securing continuity of eddy covariance flux time-series after changing the measurement height: Correction for flux differences due to the footprint difference

Abstract

© 2023During long-term flux monitoring, we occasionally encounter situations where the existing measurement setup must be changed. Considering that one of the main purposes of long-term flux monitoring is identifying long-term variability and trends, which are relatively small, it is important to understand or correct for flux differences caused by the measurement setting changes. In this study, before changing the flux measurement height of the CRK (Cheorwon Rice paddy, Korea) site from 10 m to 5 m, we installed another eddy covariance system at 5 m and compared the sensible and H2O/CO2/CH4 fluxes at both heights from April 2020 to April 2021. Although random errors could explain substantial portions of the flux differences between the two heights, it was confirmed that systematic errors also existed because the means of the flux differences were not zero, and the distributions of the flux differences were also significantly skewed. Further analysis showed that the primary cause of these systematic errors was the footprint differences rather than the difference in turbulent transport between the two heights. Based on the results, we proposed a strategy for securing the continuity of the flux time-series, which is necessary to understand the long-term variability using all data before and after a measurement change, and discussed the necessity of such a comparative observation.