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@ARTICLE{Post:203175,
      author       = {Post, H. and Hendricks-Franssen, Harrie-Jan and Graf,
                      Alexander and Schmidt, Marius and Vereecken, H.},
      title        = {{U}ncertainty analysis of eddy covariance {CO}2 flux
                      measurements for different {EC} tower distances using an
                      extended two-tower approach},
      journal      = {Biogeosciences},
      volume       = {12},
      number       = {4},
      issn         = {1726-4189},
      address      = {Katlenburg-Lindau [u.a.]},
      publisher    = {Copernicus},
      reportid     = {FZJ-2015-05180},
      pages        = {1205 - 1221},
      year         = {2015},
      abstract     = {The use of eddy covariance (EC) CO2 flux measurements in
                      data assimilation and other applications requires an
                      estimate of the random uncertainty. In previous studies, the
                      (classical) two-tower approach has yielded robust
                      uncertainty estimates, but care must be taken to meet the
                      often competing requirements of statistical independence
                      (non-overlapping footprints) and ecosystem homogeneity when
                      choosing an appropriate tower distance. The role of the
                      tower distance was investigated with help of a roving
                      station separated between 8 m and 34 km from a permanent EC
                      grassland station. Random uncertainty was estimated for five
                      separation distances with the classical two-tower approach
                      and an extended approach which removed systematic
                      differences of CO2 fluxes measured at two EC towers. This
                      analysis was made for a data set where (i) only similar
                      weather conditions at the two sites were included, and (ii)
                      an unfiltered one. The extended approach, applied to
                      weather-filtered data for separation distances of 95 and 173
                      m gave uncertainty estimates in best correspondence with an
                      independent reference method. The introduced correction for
                      systematic flux differences considerably reduced the
                      overestimation of the two-tower based uncertainty of net CO2
                      flux measurements and decreased the sensitivity of results
                      to tower distance. We therefore conclude that corrections
                      for systematic flux differences (e.g., caused by different
                      environmental conditions at both EC towers) can help to
                      apply the two-tower approach to more site pairs with less
                      ideal conditions.},
      cin          = {IBG-3},
      ddc          = {570},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255)},
      pid          = {G:(DE-HGF)POF3-255},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000358044200002},
      doi          = {10.5194/bg-12-1205-2015},
      url          = {https://juser.fz-juelich.de/record/203175},
}