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| Titel |
Feasibility study on footprint-based spatial flux decomposition from multiple eddy covariance measurements in a mosaic landscape |
| VerfasserIn |
Alexander Graf, Anneke van de Boer, Arnold F. Moene, Dirk Schüttemeyer, Harrie-Jan Hendricks-Franssen |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051386
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| Zusammenfassung |
| Various "natural tracer experiments" that have been successfully performed during the last
decade, indicate that there is a potential of estimating true surface fluxes from (too) small
landscape units from spatially distributed flux measurements (Göckede et al., 2006; Reth et
al., 2005). More recently, first such efforts have been presented mainly for airborne
measurements (Mauder et al., 2008; Hutjes et al., 2010) but also for a ground-based set-up
consisting of 2 stations and fields (Neftel et al., 2007). On the other hand, it has been pointed
out that footprint models may easily be overcharged by efforts to inversely determine fluxes
(Schmid, 2006).
On this poster, we present a first effort to transfer the existing approaches to a local station
network of seven eddy covariance sensor pairs installed 100 to 500 m apart in a
flat agricultural landscape dominated by three land use types. Fluxes measured
include the sensible and latent heat flux as well as CO2 flux. The footprint models
by Hsieh et al. (2000) and Kormann and Meixner (2001) are used to quantify the
contribution of each land use type to the flux measured at each station (van de Boer et al.,
2011).
Various ways to (i) estimate land use type fluxes from station fluxes and the footprint
contribution matrix and (ii) identify situations where this approach may be inapplicable are
tested against each other, as well as against independent reference measurements. The latter
are obtained from stations left out of the inversion process (cross validation) and, for the
special case of CO2 flux from a harvested field, area-averaged chamber measurements of soil
respiration. Our preliminary results indicate that spatial flux decomposition can indeed
help to reduce large footprint-induced errors. In particular, this is the case for bare
field soil respiration measurements, which are highly sensitive to contamination by
photosynthetic CO2 flux signals from surrounding cropped fields. However, the
correction also adds a high amount of uncertainty, which can be attributed both to the
footprint modelling process, and the treatment of residuals during the inversion
process.
References
Göckede, M., Markkanen, T., Mauder, M., Arnold, K., leps, J.P., Foken, T. (2005): Validation of
footprint models using natural tracer measurements from a field experiment. Agric. For. Meteorol.
135:314-325.
Hsieh, C.I., Katul, G., Chi, T.: 2000. An Approximate Analytical Model for Footprint
Estimation of Scalar Fluxes in Thermally Stratified Atmospheric Flows. Adv. Water Res. 23:
765-772.
Hutjes, R.W.A., Velinga, O.S., Gioli, B., Miglietta, F. (2010): Dis-aggregation of airborne flux
measurements using footprint analysis. Agric. For. Meteorol. 150:966-983.
Kormann, R., Meixner, F.X.: 2001. An Analytical Footprint Model for Non-Neutral Stratification.
Boundary-Layer Meteorol. 99: 207-224.
Mauder, M., Desjardins, R.L., MacPherson, I. (2008): Creating surface flux maps from airborne
measurements: application to the Mackenzie Area GEWEX study MAGS 1999. Boundary-Layer
Meteorol. 129:431-450.
Neftel, A., Spirig, C., Amman, C. (2008): Application and test of a simple tool for operational
footprint evaluations. Environ. poll. 152:644-652.
Reth, S., Göckede, M., Falge, E. (2005): CO2 efflux from agricultural soils in Eastern Germany -
comparison of a closed chamber system with eddy covariance measurements. Theor Appl. Climatol.
80:105-120.
Schmid, H.P. (2006): On the "Dos" and "Don’t"s of footprint analysis in difficult conditions.
iLEAPS Specialist Workshop Flux Measurement in Difficult Conditions. 26.-28. Januar 2006, Boulder,
USA.
van de Boer, A., Graf, A., Moene, A.F., Schüttemeyer, D. (2011): Uncertainty analysis of analytical
flux footprint models. Submitted to EGU General Assembly 2011. |
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