Extended Abstract (2.1M)10.2
Comparison of open-path and closed-path eddy covariance system
Peter M. Anthoni, Max Planck Institute for Biogeochemie, Jena, Germany; and M. Unsworth, B. Law, J. Irvine, D. D. Baldocchi, O. Kolle, A. Knohl, and E. D. Schulze
During 54 days in Summer 2000 CO2 and energy fluxes were measured with an open-path (OP, Licor Li7500) and a closed-path (CP, Licor Li6262) based eddy covariance system at a young ponderosa pine site. Good agreement between measured half-hour CO2 fluxes by the open-path (Fc.op) and the closed-path (Fc.cp) based system were found (Fc.cp=1.033 * Fc.op + 0.706 µmol m-2 s-1, n=2475, r2=0.95) , but consistent small differences are evident at night, with the CP system estimating ~1.0 µmol m-2 s-1 higher respiration on average. Daytime differences between the OP and CP systems were smaller, with the CP system estimating ~0.4 µmol m-2 s-1 lower Fc during the daytime. Overall differences between OP and CP systems appeared to be systematic and lead to a significant different estimate of cumulative net ecosystem exchange (NEE). Cumulative NEE over the 54 days was a net uptake of -33 gC m-2 for the CP system and -72 gC m-2 for the OP system, i.e. the CP estimate was 54% smaller than the OP estimate. Additional comparison above other ecosystem (Winter wheat after harvest, old-growth deciduous forest) seem to indicate a similar pattern. This presentation will discuss influences of co-spectral decomposition, density flux term (Webb et al, 1980), and corrections for frequency response loss.
Session 10, Carbon dioxide exchange Part 2
Friday, 24 May 2002, 8:30 AM-11:45 AM
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