scholarly journals Eddy covariance flux errors due to random and systematic timing errors during data acquisition

2018 ◽  
Vol 15 (17) ◽  
pp. 5473-5487 ◽  
Author(s):  
Gerardo Fratini ◽  
Simone Sabbatini ◽  
Kevin Ediger ◽  
Brad Riensche ◽  
George Burba ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
High Frequency ◽  
Digital Systems ◽  
Data Logging ◽  
Timing Errors ◽  
Synchronization Errors ◽  
Cutoff Frequencies ◽  
Error Magnitude ◽  
Transmission Reliability ◽  
Significant Flux

Abstract. Modern eddy covariance (EC) systems collect high-frequency data (10–20 Hz) via digital outputs of instruments. This is an important evolution with respect to the traditional and widely used mixed analog/digital systems, as fully digital systems help overcome the traditional limitations of transmission reliability, data quality, and completeness of the datasets. However, fully digital acquisition introduces a new problem for guaranteeing data synchronicity when the clocks of the involved devices themselves cannot be synchronized, which is often the case with instruments providing data via serial or Ethernet connectivity in a streaming mode. In this paper, we suggest that, when assembling EC systems “in-house”, aspects related to timing issues need to be carefully considered to avoid significant flux biases. By means of a simulation study, we found that, in most cases, random timing errors can safely be neglected, as they do not impact fluxes significantly. At the same time, systematic timing errors potentially arising in asynchronous systems can effectively act as filters leading to significant flux underestimations, as large as 10 %, by means of attenuation of high-frequency flux contributions. We characterized the transfer function of such “filters” as a function of the error magnitude and found cutoff frequencies as low as 1 Hz, implying that synchronization errors can dominate high-frequency attenuations in open- and enclosed-path EC systems. In most cases, such timing errors neither be detected nor characterized a posteriori. Therefore, it is important to test the ability of traditional and prospective EC data logging systems to assure the required synchronicity and propose a procedure to implement such a test relying on readily available equipment.

scholarly journals Eddy Covariance flux errors due to random and systematic timing errors during data acquisition

2018 ◽  
Author(s):  
Gerardo Fratini ◽  
Simone Sabbatini ◽  
Kevin Ediger ◽  
Giacomo Nicolini ◽  
Domenico Vitale ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
High Frequency ◽  
Digital Systems ◽  
High Frequency Data ◽  
Asynchronous Systems ◽  
A Posteriori ◽  
Frequency Data ◽  
Data Logging ◽  
Timing Errors ◽  
Synchronization Errors

Abstract. Modern Eddy Covariance (EC) systems collect high-frequency data (10–20 Hz) via instruments’ digital outputs. While this helps overcome the limits of traditional mixed analog/digital systems, it also introduces the new problem of guaranteeing data synchronicity when the clocks of the involved devices cannot themselves be synchronized, which is often the case with instruments providing data via serial or Ethernet connectivity. By means of a simulation study, we found that in most cases random timing errors can safely be neglected, as they do not impact fluxes to a large extent. On the contrary, realistic systematic timing errors potentially arising in asynchronous systems can lead to flux underestimations as large as 10 %, by means of attenuation of high-frequency flux contributions. We characterize the transfer function of such filters as a function of the error amount and find cut-off frequencies as low as 1 Hz, which means that synchronization errors can dominate high-frequency attenuations in open- and enclosed-path EC systems. In most cases, such timing errors cannot be detected nor quantified a posteriori. Therefore, we suggest testing the ability of prospect EC data logging systems to assure required synchronicity and propose a procedure to implement such a test, which relies on readily available equipment.

scholarly journals Source partitioning of H<sub>2</sub>O and CO<sub>2</sub> fluxes based on high-frequency eddy covariance data: a comparison between study sites

2019 ◽  
Vol 16 (6) ◽  
pp. 1111-1132 ◽  
Author(s):  
Anne Klosterhalfen ◽  
Alexander Graf ◽  
Nicolas Brüggemann ◽  
Clemens Drüe ◽  
Odilia Esser ◽  
...  
Keyword(s):  
Soil Respiration ◽  
Eddy Covariance ◽  
High Frequency ◽  
Canopy Height ◽  
Canopy Density ◽  
Partitioning Methods ◽  
Site Characteristics ◽  
Measurement Height ◽  
Study Sites ◽  
Source Partitioning

Abstract. For an assessment of the roles of soil and vegetation in the climate system, a further understanding of the flux components of H2O and CO2 (e.g., transpiration, soil respiration) and their interaction with physical conditions and physiological functioning of plants and ecosystems is necessary. To obtain magnitudes of these flux components, we applied source partitioning approaches after Scanlon and Kustas (2010; SK10) and after Thomas et al. (2008; TH08) to high-frequency eddy covariance measurements of 12 study sites covering different ecosystems (croplands, grasslands, and forests) in different climatic regions. Both partitioning methods are based on higher-order statistics of the H2O and CO2 fluctuations, but proceed differently to estimate transpiration, evaporation, net primary production, and soil respiration. We compared and evaluated the partitioning results obtained with SK10 and TH08, including slight modifications of both approaches. Further, we analyzed the interrelations among the performance of the partitioning methods, turbulence characteristics, and site characteristics (such as plant cover type, canopy height, canopy density, and measurement height). We were able to identify characteristics of a data set that are prerequisites for adequate performance of the partitioning methods. SK10 had the tendency to overestimate and TH08 to underestimate soil flux components. For both methods, the partitioning of CO2 fluxes was less robust than for H2O fluxes. Results derived with SK10 showed relatively large dependencies on estimated water use efficiency (WUE) at the leaf level, which is a required input. Measurements of outgoing longwave radiation used for the estimation of foliage temperature (used in WUE) could slightly increase the quality of the partitioning results. A modification of the TH08 approach, by applying a cluster analysis for the conditional sampling of respiration–evaporation events, performed satisfactorily, but did not result in significant advantages compared to the original method versions developed by Thomas et al. (2008). The performance of each partitioning approach was dependent on meteorological conditions, plant development, canopy height, canopy density, and measurement height. Foremost, the performance of SK10 correlated negatively with the ratio between measurement height and canopy height. The performance of TH08 was more dependent on canopy height and leaf area index. In general, all site characteristics that increase dissimilarities between scalars appeared to enhance partitioning performance for SK10 and TH08.

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

2013 ◽  
Vol 19 ◽  
pp. 293-302 ◽  
Author(s):  
D. Masseroni ◽  
C. Corbari ◽  
A. Ceppi ◽  
C. Gandolfi ◽  
M. Mancini
Keyword(s):  
Eddy Covariance ◽  
High Frequency ◽  
High Frequency Data ◽  
Frequency Data ◽  
Eddy Covariance Measurements

scholarly journals Measurements and quality control of ammonia eddy covariance fluxes: a new strategy for high-frequency attenuation correction

2019 ◽  
Vol 12 (11) ◽  
pp. 6059-6078 ◽  
Author(s):  
Alexander Moravek ◽  
Saumya Singh ◽  
Elizabeth Pattey ◽  
Luc Pelletier ◽  
Jennifer G. Murphy
Keyword(s):  
Detection Limit ◽  
Eddy Covariance ◽  
Attenuation Correction ◽  
High Frequency ◽  
Direct Method ◽  
Time Response ◽  
Trace Gas ◽  
Horizontal Wind ◽  
Nh3 Adsorption ◽  
Flux Loss

Abstract. Measurements of the surface–atmosphere exchange of ammonia (NH3) are necessary to study the emission and deposition processes of NH3 from managed and natural ecosystems. The eddy covariance technique, which is the most direct method for trace gas exchange measurements at the ecosystem level, requires trace gas detection at a fast sample frequency and high precision. In the past, the major limitation for measuring NH3 eddy covariance fluxes has been the slow time response of NH3 measurements due to NH3 adsorption on instrument surfaces. While high-frequency attenuation correction methods are used, large uncertainties in these corrections still exist, which are mainly due to the lack of understanding of the processes that govern the time response. We measured NH3 fluxes over a corn crop field using a quantum cascade laser spectrometer (QCL) that enables measurements of NH3 at a 10 Hz measurement frequency. The 5-month measurement period covered a large range of environmental conditions that included both periods of NH3 emission and deposition and allowed us to investigate the time response controlling parameters under field conditions. Without high-frequency loss correction, the median daytime NH3 flux was 8.59 ng m−2 s−1 during emission and −19.87 ng m−2 s−1 during deposition periods, with a median daytime random flux error of 1.61 ng m−2 s−1. The overall median flux detection limit was 2.15 ng m−2 s−1, leading to only 11.6 % of valid flux data below the detection limit. From the flux attenuation analysis, we determined a median flux loss of 17 % using the ogive method. No correlations of the flux loss with environmental or analyser parameters (such as humidity or inlet ageing) were found, which was attributed to the uncertainties in the ogive method. Therefore, we propose a new method that simulates the flux loss by using the analyser time response that is determined frequently over the course of the measurement campaign. A correction that uses as a function of the horizontal wind speed and the time response is formulated which accounts for surface ageing and contamination over the course of the experiment. Using this method, the median flux loss was calculated to be 46 %, which was substantially higher than with the ogive method.

scholarly journals Technical note: Water vapour concentration and flux measurements with PTR-MS

2006 ◽  
Vol 6 (3) ◽  
pp. 5329-5355 ◽  
Author(s):  
C. Ammann ◽  
A. Brunner ◽  
C. Spirig ◽  
A. Neftel
Keyword(s):  
Water Vapour ◽  
Eddy Covariance ◽  
High Frequency ◽  
Reference System ◽  
Transfer Functions ◽  
Terrestrial Ecosystems ◽  
Water Vapour Flux ◽  
Water Vapour Concentration ◽  
Vapour Concentration ◽  
Vapour Flux

Abstract. The most direct approach for measuring the exchange of biogenic volatile organic compounds between terrestrial ecosystems and the atmosphere is the eddy covariance technique. It has been applied several times in the last few years using fast response proton-transfer-reaction mass spectrometry (PTR-MS). We present an independent validation of this technique by applying it to measure the water vapour flux in comparison to a common reference system comprising an infra-red gas analyser (IRGA). Water vapour was detected in the PTR-MS at mass 37 (atomic mass units) corresponding to the cluster ion H3O+·H2O. During a five-week field campaign at a grassland site, we obtained a non-linear but stable calibration function between the mass 37 signal and the reference water vapour concentration. With a correction of the high-frequency damping loss based on empirical ogive analysis, the eddy covariance water vapour flux obtained with the PTR-MS showed a very good agreement with the flux of the reference system. The application of the empirical ogive method for high-frequency correction led to significantly better results than using a correction based on theoretical spectral transfer functions. This finding is attributed to adsorption effects on the tube walls that are presently not included in the theoretical correction approach.

scholarly journals InnFLUX – an open-source code for conventional and disjunct eddy covariance analysis of trace gas measurements: an urban test case

2020 ◽  
Vol 13 (3) ◽  
pp. 1447-1465 ◽  
Author(s):  
Marcus Striednig ◽  
Martin Graus ◽  
Tilmann D. Märk ◽  
Thomas G. Karl
Keyword(s):  
Open Source ◽  
Eddy Covariance ◽  
High Frequency ◽  
Urban Canopy ◽  
Lag Time ◽  
Trace Gas ◽  
High Temporal Resolution ◽  
Eddy Covariance Method ◽  
Wide Range ◽  
Gas Measurements

Abstract. We describe and test a new versatile software tool for processing eddy covariance and disjunct eddy covariance flux data. We present an evaluation based on urban non-methane volatile organic compound (NMVOC) measurements using a proton transfer reaction quadrupole interface time-of-flight mass spectrometer (PTR-QiTOF-MS) at the Innsbruck Atmospheric Observatory. The code is based on MATLAB® and can be easily configured to process high-frequency, low-frequency and disjunct data. It can be applied to a wide range of analytical setups for NMVOC and other trace gas measurements, and is tailored towards the application of noisy data, where lag time corrections become challenging. Several corrections and quality control routines are implemented to obtain the most reliable results. The software is open source, so it can be extended and adjusted to specific purposes. We demonstrate the capabilities of the code based on a large urban dataset collected in Innsbruck, Austria, where three-dimensional winds and ambient concentrations of NMVOCs and auxiliary trace gases were sampled with high temporal resolution above an urban canopy. Concomitant measurements of 12C and 13C isotopic NMVOC fluxes allow testing algorithms used for determination of flux limits of detection (LOD) and lag time analysis. We use the high-frequency NMVOC dataset to generate a set of disjunct data and compare these results with the true eddy covariance method. The presented analysis allows testing the theory of disjunct eddy covariance (DEC) in an urban environment. Our findings confirm that the disjunct eddy covariance method can be a reliable tool, even in complex urban environments when fast sensors are not available, but that the increase in random error impedes the ability to detect small fluxes due to higher flux LODs.

scholarly journals A performance evaluation of despiking algorithms for eddy covariance data

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Domenico Vitale
Keyword(s):  
Eddy Covariance ◽  
Data Center ◽  
High Frequency ◽  
Complex Dynamics ◽  
Simulated Data ◽  
Quality Standard ◽  
High Quality Standard ◽  
High Level ◽  
Essential Prerequisite ◽  
Better Than

AbstractSpike detection for raw high-frequency eddy covariance time series is a challenging task because of the confounding effect caused by complex dynamics and the high level of noise affecting such data. To cope with these features, a new despiking procedure rooted on robust functionals is proposed. By processing simulated data, it is demonstrated that the proposed procedure performs better than the existing algorithms and can be therefore considered as a candidate for the implementation in data center environmental monitoring systems, where the availability of automatic procedures ensuring a high quality standard of released products constitutes an essential prerequisite.

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