scholarly journals Eddy covariance carbonyl sulphide flux measurements with a quantum cascade laser absorption spectrometer

2016 ◽  
Author(s):  
Katharina Gerdel ◽  
Felix M. Spielmann ◽  
Albin Hammerle ◽  
Georg Wohlfahrt
Keyword(s):  
Eddy Covariance ◽  
High Frequency ◽  
Trace Gas ◽  
Quantum Cascade ◽  
Laser Absorption ◽  
Low Pass ◽  
Flux Measurements ◽  
Carbonyl Sulphide ◽  
High Pass ◽  
Processing Steps

Abstract. The trace gas carbonyl sulphide (COS) has lately received growing interest in the eddy covariance (EC) community due to its potential to serve as an independent approach for constraining gross primary production and canopy stomatal conductance. Thanks to recent developments of fast-response high-precision trace gas analysers (e.g. quantum cascade laser absorption spectrometers (QCLAS)), a handful of EC COS flux measurements have been published since 2013. To date, however, a thorough methodological characterisation of QCLAS with regard to the requirements of the EC technique and the necessary processing steps has not been conducted. The objective of this study is to provide for the first time a rigorous analysis of the most widely used QCLAS model for making defensible EC COS flux measurements. Data were collected from May to October 2015 at a temperate mountain grassland in Tyrol, Austria. Analysis of the Allan variance of high-frequency concentration measurements revealed laser drift to occur under field conditions after an averaging time of around 50 s. We thus explored the use of two high-pass filtering approaches (linear detrending and recursive filtering) as opposed to block averaging for covariance computation. Spectral analysis revealed considerable noise at higher frequencies, appearing to influence the high-frequency region of co-spectra (and therefore covariances). By applying a finite-impulse response filter we removed the noise-affected spectral region. The effects of this digital high- and low-pass filtering, and additional low-pass filtering due to the eddy covariance system design, were corrected for using a site-specific reference model co-spectrum and a series of transfer functions. An independent validation of these post-processing steps was achieved by comparison of the CO2 and H2O flux measurements obtained with the QCLAS against those obtained with a closed-path infrared gas analyser. While the validation showed good correspondence and minor statistical differences between the three different high-pass filtering approaches – the benefits of high pass filtering clearly emerged as a reduction of the random flux uncertainty and a higher fraction of data passing the applied QA/QC criterions. We conclude that the most widely used QCLAS can be used to make defensible COS flux measurements provided the appropriate corrections are applied.

scholarly journals Eddy covariance carbonyl sulfide flux measurements with a quantum cascade laser absorption spectrometer

2017 ◽  
Vol 10 (9) ◽  
pp. 3525-3537 ◽  
Author(s):  
Katharina Gerdel ◽  
Felix Maximilian Spielmann ◽  
Albin Hammerle ◽  
Georg Wohlfahrt
Keyword(s):  
Eddy Covariance ◽  
Quantum Cascade Laser ◽  
Gross Primary Production ◽  
Carbonyl Sulfide ◽  
Linear Interpolation ◽  
Trace Gas ◽  
Quantum Cascade ◽  
Laser Absorption ◽  
Flux Measurements ◽  
High Pass

Abstract. The trace gas carbonyl sulfide (COS) has lately received growing interest from the eddy covariance (EC) community due to its potential to serve as an independent approach for constraining gross primary production and canopy stomatal conductance. Thanks to recent developments of fast-response high-precision trace gas analysers (e.g. quantum cascade laser absorption spectrometers, QCLAS), a handful of EC COS flux measurements have been published since 2013. To date, however, a thorough methodological characterisation of QCLAS with regard to the requirements of the EC technique and the necessary processing steps has not been conducted. The objective of this study is to present a detailed characterisation of the COS measurement with the Aerodyne QCLAS in the context of the EC technique and to recommend best EC processing practices for those measurements. Data were collected from May to October 2015 at a temperate mountain grassland in Tyrol, Austria. Analysis of the Allan variance of high-frequency concentration measurements revealed the occurrence of sensor drift under field conditions after an averaging time of around 50 s. We thus explored the use of two high-pass filtering approaches (linear detrending and recursive filtering) as opposed to block averaging and linear interpolation of regular background measurements for covariance computation. Experimental low-pass filtering correction factors were derived from a detailed cospectral analysis. The CO2 and H2O flux measurements obtained with the QCLAS were compared with those obtained with a closed-path infrared gas analyser. Overall, our results suggest small, but systematic differences between the various high-pass filtering scenarios with regard to the fraction of data retained in the quality control and flux magnitudes. When COS and CO2 fluxes are combined in the ecosystem relative uptake rate, systematic differences between the high-pass filtering scenarios largely cancel out, suggesting that this relative metric represents a robust key parameter comparable between studies relying on different post-processing schemes.

scholarly journals Towards standardized processing of eddy covariance flux measurements of carbonyl sulfide

2020 ◽  
Vol 13 (7) ◽  
pp. 3957-3975
Author(s):  
Kukka-Maaria Kohonen ◽  
Pasi Kolari ◽  
Linda M. J. Kooijmans ◽  
Huilin Chen ◽  
Ulli Seibt ◽  
...  
Keyword(s):  
Data Processing ◽  
Eddy Covariance ◽  
High Frequency ◽  
Signal To Noise Ratio ◽  
Time Lag ◽  
Carbonyl Sulfide ◽  
Signal To Noise ◽  
Flux Measurements ◽  
Noise Ratio ◽  
Processing Steps

Abstract. Carbonyl sulfide (COS) flux measurements with the eddy covariance (EC) technique are becoming popular for estimating gross primary productivity. To compare COS flux measurements across sites, we need standardized protocols for data processing. In this study, we analyze how various data processing steps affect the calculated COS flux and how they differ from carbon dioxide (CO2) flux processing steps, and we provide a method for gap-filling COS fluxes. Different methods for determining the time lag between COS mixing ratio and the vertical wind velocity (w) resulted in a maximum of 15.9 % difference in the median COS flux over the whole measurement period. Due to limited COS measurement precision, small COS fluxes (below approximately 3 pmol m−2 s−1) could not be detected when the time lag was determined from maximizing the covariance between COS and w. The difference between two high-frequency spectral corrections was 2.7 % in COS flux calculations, whereas omitting the high-frequency spectral correction resulted in a 14.2 % lower median flux, and different detrending methods caused a spread of 6.2 %. Relative total uncertainty was more than 5 times higher for low COS fluxes (lower than ±3 pmol m−2 s−1) than for low CO2 fluxes (lower than ±1.5 µmol m−2 s−1), indicating a low signal-to-noise ratio of COS fluxes. Due to similarities in ecosystem COS and CO2 exchange, we recommend applying storage change flux correction and friction velocity filtering as usual in EC flux processing, but due to the low signal-to-noise ratio of COS fluxes, we recommend using CO2 data for time lag and high-frequency corrections of COS fluxes due to the higher signal-to-noise ratio of CO2 measurements.

scholarly journals Options to correct local turbulent flux measurements for large-scale fluxes using a LES-based approach

2021 ◽  
Author(s):  
Matthias Mauder ◽  
Andreas Ibrom ◽  
Luise Wanner ◽  
Frederik De Roo ◽  
Peter Brugger ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Large Scale ◽  
Heat Fluxes ◽  
Eddy Covariance Method ◽  
Boundary Layer Height ◽  
Secondary Circulations ◽  
Low Pass ◽  
Measurement Height ◽  
Flux Measurements ◽  
Dispersive Fluxes

Abstract. The eddy-covariance method provides the most direct estimates for fluxes between ecosystems and the atmosphere. However, dispersive fluxes can occur in the presence of secondary circulations, which can inherently not be captured by such single-tower measurements. In this study, we present options to correct local flux measurements for such large-scale transport based on a non-local parametric model that has been developed from a set of idealized LES runs for three real-world sites. The test sites DK-Sor, DE-Fen, and DE-Gwg, represent typical conditions in the mid-latitudes with different measurement height, different terrain complexity and different landscape-scale heterogeneity. Different ways to determine the boundary-layer height, which is a necessary input variable for modelling the dispersive fluxes, are applied, either from operational radio-soundings and local in-situ measurements for the flat site or from backscatter-intensity profile obtained from collocated ceilometers for the two sites in complex terrain. The adjusted total fluxes are evaluated by assessing the improvement in energy balance closure and by comparing the resulting latent heat fluxes with evapotranspiration rates from nearby lysimeters. The results show that not only the accuracy of the flux estimates is improved but also the precision, which is indicated by RMSE values that are reduced by approximately 50 %. Nevertheless, it needs to be clear that this method is intended to correct for a bias in eddy-covariance measurements due to the presence of large-scale dispersive fluxes. Other reasons potentially causing a systematic under- or overestimation, such as low-pass filtering effects and missing storage terms, still need to be considered and minimized as much as possible. Moreover, additional transport induced by surface heterogeneities is not considered.

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.

A Novel High-Pass Filters Implementation by Fully Differential Op Amp Integrators

2012 ◽  
Vol 229-231 ◽  
pp. 1531-1534
Author(s):  
Hai Dan Zhang ◽  
Hu Bao ◽  
Den Gan Chen ◽  
Jing Yu
Keyword(s):  
High Frequency ◽  
Circuit Complexity ◽  
Simulation Method ◽  
Signal Flow Graph ◽  
Fully Differential ◽  
Op Amp ◽  
Low Pass ◽  
Frequency Properties ◽  
High Pass ◽  
Excessive Noise

The design of low-pass and bandpass filters is often based on the leapfrog method which, in these cases, yields integrator-based structures. Using the leapfrog signal flow graph (SFG) for the simulation of high-pass filters leads to a differentiator-based structure which could be implemented by Gm-C or CCII conveniently. However, when we use Op amp RC integrators for good linearity, we have to use integrators, and not differentiators, for reasons related to the excessive noise behavior of the latter. This paper presents a new leapfrog SFG implementation by fully differential Op amp integrators, which combines good high-frequency properties with good noise properties. The direct SFG simulation method and single-ended output Op amp can also based on integrators, but all of them will lead to a relatively high circuit complexity and a high noise level. A design example is included, with comparisons of gain responses and noise densities.

Evaluation of Laser Absorption Spectroscopic Techniques for Eddy Covariance Flux Measurements of Ammonia

2008 ◽  
Vol 42 (6) ◽  
pp. 2041-2046 ◽  
Author(s):  
James D. Whitehead ◽  
Marsailidh Twigg ◽  
Daniela Famulari ◽  
Eiko Nemitz ◽  
Mark A. Sutton ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Spectroscopic Techniques ◽  
Laser Absorption ◽  
Flux Measurements

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 Disjunct eddy covariance technique for trace gas flux measurements

2001 ◽  
Vol 28 (16) ◽  
pp. 3139-3142 ◽  
Author(s):  
H. J. I. Rinne ◽  
A. B. Guenther ◽  
C. Warneke ◽  
J. A. de Gouw ◽  
S. L. Luxembourg
Keyword(s):  
Eddy Covariance ◽  
Trace Gas ◽  
Gas Flux ◽  
Eddy Covariance Technique ◽  
Flux Measurements

scholarly journals Sum of Sine Modeling Approach as a New Processing Technique For a Biometric System Based on ECG Signal

2020 ◽  
Vol 14 ◽  
Keyword(s):  
Processing Technique ◽  
Features Extraction ◽  
Human Beings ◽  
Biometric System ◽  
Literature Study ◽  
Mode Decomposition ◽  
Low Pass ◽  
New Processing ◽  
High Pass ◽  
Processing Steps

Biometrics is considered in current research as one of the best methods for authenticating human beings. In our paper, the heartbeat biometric, also called Electrocardiographic (ECG), is working on. This biometric is chosen because human ECGs cannot be falsely created and replicated. This study aims to find the best features from this biometric that can identify a person, given the extractions and classification algorithms for the heartbeat biometric signal. Depending on a literature study we work to propose a new and more efficient technique based on a new method for ECG features extraction and these features will be the inputs for pattern recognition classifier. This methodology will be tested on real experimental ECG data that is collected. The Data collected from 10 subjects by a commercial ECG device taking the data from lead 1. The pre-processing steps start with the Empirical Mode Decomposition (EMD) before digital filters which are: low pass, high pass, and derivative pass filters. Features extraction steps are peak detection, segmentation, and wave modeling for each segment. The classification used the Multi-Layer Perceptron and compared it to classification using Radial Basis Function were the results of MLP were much better for these applications since the accuracy of the final results of MLP is 99% and that related to the RBF is 95%.

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