Operative Use of Eddy Covariance Measurements: Are High Frequency Data Indispensable?

Abstract

Reliable estimation of turbulent evapotranspiration and carbon dioxide fluxes is based on a correction procedure due to eddy covariance methodology and instrumental characteristics. Literature standardized methods for data processing are defined for analyzing the quality of high frequency measurements. However, for operative applications, linked to real time irrigation water management, high frequency data are difficult to manage. So the objective of this paper is to verify the possibility of using eddy covariance data in an operative way in order to understand if averaged data at 30minutes are still of good quality in relation to those obtained from high frequency measurements. Data have been collected by an eddy covariance station over a maize field at Livraga (Lodi, Italy) for the year 2012. High frequency data (20Hz) and averaged data (30minutes) are collected separately in a PCMICA of 2Gb capacity and data logger memory respectively. High frequency data are analyzed with Eddy Pro 4.0 open source software. Effects of different types of corrections, from axis rotation to density fluctuations, are shown. Spectral correction factors have been calculated and flux losses are estimated. Quality of corrected fluxes and energy balance closure are also shown. Averaged data have been analyzed with Polimi Eddy Covariance software (PEC) which accounts only a portion of the correction procedures which can be applied to high frequency data, where the major difference is linked to the absence of the spectra correction. Evapotranspiration and carbon dioxide fluxes from high frequency and average data are then compared and cumulated trends over the growing season are assessed and a small difference is found. So these comparisons highlight the possibility of using averaged data for operative water management without drastically decreasing the quality of fluxes.