Quality control of CarboEurope flux data – Part 1: Coupling footprint analyses with flux data quality assessment to evaluate sites in forest ecosystems

Mathias Göckede ,J Banza,G Seufert,M J Sanz,Renate Koeble ,Thomas Foken ,Arnaud Carrara ,Mika Aurela ,Lukas Siebicke ,Yves Brunet ,Timo Vesala ,Corinna Rebmann ,Jean‐François Soussana ,Bernard Longdoz ,Robert Clement ,Marc Aubinet ,Jürg Fuhrer ,Alexander Knohl ,Leonardo Montagnani ,Kim Pilegaard ,Tiina Markkanen ,Mirco Migliavacca ,Hans Verbeeck ,Bernard Heinesch ,Serge Rambal ,Abel Rodrigues ,Jean-Marc Bonnefond ,John Moncrieff ,Thomas Grünwald ,E.j Moors ,João Mateus ,Jean‐Marc Ourcival ,Werner Eugster ,J S Pereira ,Giovanni Manca ,André Granier ,Matthias Mauder ,Eyal Rotenberg ,Pavel Sedlák ,Giorgio Matteucci ,Tuomas Laurila ,Michal V Marek ,Stefano Minerbi ,Gabriel Pita ,Ebba Dellwik ,Ivan A Janssens ,Dario Papale ,Christian Bernhofer ,Riccardo Valentini ,J.a Elbers ,Dan Yakir

doi:10.5194/bg-5-433-2008

Abstract

Abstract. We applied a site evaluation approach combining Lagrangian Stochastic footprint modeling with a quality assessment approach for eddy-covariance data to 25 forested sites of the CarboEurope-IP network. The analysis addresses the spatial representativeness of the flux measurements, instrumental effects on data quality, spatial patterns in the data quality, and the performance of the coordinate rotation method. Our findings demonstrate that application of a footprint filter could strengthen the CarboEurope-IP flux database, since only one third of the sites is situated in truly homogeneous terrain. Almost half of the sites experience a significant reduction in eddy-covariance data quality under certain conditions, though these effects are mostly constricted to a small portion of the dataset. Reductions in data quality of the sensible heat flux are mostly induced by characteristics of the surrounding terrain, while the latent heat flux is subject to instrumentation-related problems. The Planar-Fit coordinate rotation proved to be a reliable tool for the majority of the sites using only a single set of rotation angles. Overall, we found a high average data quality for the CarboEurope-IP network, with good representativeness of the measurement data for the specified target land cover types.

Highlights

Continuous monitoring of fluxes between biosphere and atmosphere using the eddy-covariance technique (e.g. Aubinet et al, 2000; Baldocchi et al, 2000) has become an important tool to improve understanding of the role of different types of ecosystems as sources or sinks for greenhouse gases, with a particular focus on CO2
In the case of the PT-Mi1 site which is situated in rather open savanna forest, possible explanations include a distortion of the wind field by individual trees close to the tower, or a flow distortion by the inlet tube of the infra-red gas analyzer (IRGA) system which partly obstructs the sonic anemometer in the disturbed wind sectors
This study applied the site evaluation approach by Gockede et al (2006), which combines Lagrangian Stochastic footprint modeling with a quality assessment approach for eddycovariance data (Foken et al, 2004) to 25 forested sites of the CarboEurope-IP network

Summary

Introduction

Continuous monitoring of fluxes between biosphere and atmosphere using the eddy-covariance technique (e.g. Aubinet et al, 2000; Baldocchi et al, 2000) has become an important tool to improve understanding of the role of different types of ecosystems as sources or sinks for greenhouse gases, with a particular focus on CO2. Gockede et al (2004) combined a flux data quality assessment approach (Foken et al, 2004) with analytic footprint modeling (Schmid, 1994, 1997) to identify correlations between flux data quality and characteristics of the terrain surrounding the flux site. Their approach was successfully applied by Rebmann et al (2005) on 18 forest sites of the CARBOEUROFLUX network

Results

Discussion

Conclusion