[684] - Validation of a minimum microclimate disturbance chamber for net ecosystem flux measurements

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Graf, A., Werner, J., Langensiepen, M., van de Boer, A., Schmidt, M., Kupisch, M., Vereecken, H., 2013. Validation of a minimum microclimate disturbance chamber for net ecosystem flux measurements. Agricultural and Forest Meteorology, 174-175, 1 - 14. DOI: 10.1016/j.agrformet.2013.02.001.
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Title(s):Main Title: Validation of a minimum microclimate disturbance chamber for net ecosystem flux measurements
Description(s):Abstract: A minimum-disturbance chamber for canopy net CO2 and H2O flux measurements is described. Thesystem is a passively (optionally actively) ventilated tunnel with large (similar to 0.14 m2) in- and outletcross sections covering a surface area of approximately 1.6 m2. A differential, non-drying closed-path gasanalyzer is used to minimize the requirement for concentration build-ups or drawdowns between the inandoutlet, and 0.05 mm thick FEP (fluorinated ethylene propylene) film is used as top and wall materialto minimize radiation modifications.First measurement results in passively ventilated mode are presented from two different sites: awheat field at a lowland site in the westernmost part of Germany, and differently cropped adjacentfields in the Pyrenee foothills in France, including grassland and a cereal-dominated crop mixture forfodder production. Flux estimates derived from measurements over 20–30 min deployments were comparedto concurrent observations by three eddy covariance (EC) stations. The system compared wellto EC measurements, with bias of−6.6% for latent heat flux and +9.0% for CO2 flux (R2 = 0.78 and 0.74,respectively).The presence of the chamber causes a reduction of less than 4% in incoming shortwave radiation, andan increase of about 18% in downward longwave radiation. Near the outlet, CO2 concentration was onaverage modified by−3% with respect to outside conditions, water vapour concentration by +22%, andtemperature by +0.9 K, staying below published modifications of a comparable non-steady-state chamberclosed for 2 min. Ventilation speed varied by less than 9% across the inlet cross section. Limitations includea minimum wind speed requirement that can be set as low as 0.2 m s−1 for a raw data logging frequencyof 1 s−1 or higher, but would need to be higher for slow-response gas analyzers. At the same time, ameasurement period of 10 min or more is recommended to minimize random errors from storage termfluctuations. A correction for the added water vapour volume by evapotranspiration is derived and tested,which typically affects H2O flux itself by less than +2% and CO2 flux measurements by 1 [1]mol/J latentheat.
Identifier(s):DOI: 10.1016/j.agrformet.2013.02.001
Responsible Party
Creator(s):Author: Alexander Graf
Author: J. Werner
Author: Matthias Langensiepen
Author: Anneke van de Boer
Author: Marius Schmidt
Author: Moritz Kupisch
Author: Harry Vereecken
TR32 Topic:Vegetation
Subject(s):CRC/TR32 Keywords: CO2, Eddy Covariance, Evapotranspiration, H2O, Chamber
File Details
File Name:2013_Graf_AFM.pdf
Data Type:Text
Size(s):14 Pages
File Size:1507 kB (1.472 MB)
Date(s):Date Accepted: 2013-02-05
Mime Type:application/pdf
Data Format:PDF
Download Permission:OnlyTR32
General Access and Use Conditions:For internal use only
Access Limitations:For internal use only
Licence:TR32DB Data policy agreement
Measurement Region:Ellebach
Measurement Location:Merzenhausen
Specific Informations - Publication
Article Type:Journal
Source:Agricultural and Forest Meteorology
Number Of Pages:14
Page Range:1 - 14
Metadata Details
Metadata Creator:Alexander Graf
Metadata Created:2013-12-02
Metadata Last Updated:2013-12-02
Funding Phase:2
Metadata Language:English
Metadata Version:V40
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