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@INPROCEEDINGS{Graf:139214,
      author       = {Graf, Alexander and van de Boer, Anneke and Schüttemeyer,
                      Dirk and Moene, Arnold and Vereecken, Harry},
      title        = {{I}ntercomparison of methods for the estimation of
                      displacement height and roughness length from single-level
                      eddy covariance data},
      reportid     = {FZJ-2013-05217},
      year         = {2013},
      abstract     = {The displacement height d and roughness length z0 are
                      parameters of the logarithmic wind profile and as such these
                      are characteristics of the surface, that are required in a
                      multitude of meteorological modeling applications.
                      Classically, both parameters are estimated from multi-level
                      measurements of wind speed over a terrain sufficiently
                      homogeneous to avoid footprint-induced differences between
                      the levels. As a rule-of thumb, d of a dense, uniform crop
                      or forest canopy is 2/3 to 3/4 of the canopy height h, and
                      z0 about $10\%$ of canopy height in absence of any d.
                      However, the uncertainty of this rule-of-thumb becomes
                      larger if the surface of interest is not "dense and
                      uniform", in which case a site-specific determination is
                      required again. By means of the eddy covariance method,
                      alternative possibilities to determine z0 and d have become
                      available. Various authors report robust results if either
                      several levels of sonic anemometer measurements, or one such
                      level combined with a classic wind profile is used to
                      introduce direct knowledge on the friction velocity into the
                      estimation procedure. At the same time, however, the eddy
                      covariance method to measure various fluxes has superseded
                      the profile method, leaving many current stations without a
                      wind speed profile with enough levels sufficiently far above
                      the canopy to enable the classic estimation of z0 and d.
                      From single-level eddy covariance measurements at one point
                      in time, only one parameter can be estimated, usually z0
                      while d is assumed to be known. Even so, results tend to
                      scatter considerably. However, it has been pointed out, that
                      the use of multiple points in time providing different
                      stability conditions can enable the estimation of both
                      parameters, if they are assumed constant over the time
                      period regarded. These methods either rely on flux-variance
                      similarity (Weaver 1990 and others following), or on the
                      integrated universal function for momentum (Martano 2000 and
                      others following). In both cases, iterations over the range
                      of possible d values are necessary. We extended this set of
                      methods by a non-iterative, regression based approach. Only
                      a stability range of data is used in which the universal
                      function is known to be approximately linear. Then, various
                      types of multiple linear regression can be used to relate
                      the terms of the logarithmic wind profile equation to each
                      other, and derive z0 and d from the regression parameters.
                      Two examples each of the two existing iterative approaches,
                      and the new noniterative one are compared to each other and
                      to plausibility limits in three different agricultural
                      crops. The study contains periods of growth as well as of
                      constant crop height, also allowing for an examination of
                      the relations between z0, d, and canopy height. Results
                      indicate that estimated z0 values, even in absence of
                      prescribed d values, are fairly robust, plausible and
                      consistent across all methods. The largest deviations are
                      produced by the two fluxvariance similarity based methods.
                      Estimates of d, in contrast, can be subject to implausible
                      deviations with all methods, even after quality-filtering of
                      input data. Again, the largest deviations occur with
                      flux-variance similarity based methods. Ensemble averaging
                      between all methods can reduce this problem, offering a
                      potentially useful way of estimating d at more complex sites
                      where the rule-of-thumb cannot be applied easily. Martano P
                      (2000): Estimation of surface roughness length and
                      displacement height from single-level sonic anemometer data.
                      Journal of Applied Meteorology 39:708-715. Weaver HL (1990):
                      Temperature and Humidity flux-variance relations determined
                      by one-dimensional eddy correlation. Boundary-Layer
                      Meteorology 53:77-91.},
      month         = {Apr},
      date          = {2013-04-07},
      organization  = {EGU General Assembly 2013, Vienna
                       (Austria), 7 Apr 2013 - 12 Apr 2013},
      subtyp        = {Other},
      cin          = {IBG-3},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {246 - Modelling and Monitoring Terrestrial Systems: Methods
                      and Technologies (POF2-246) / DFG project 139819005 - Links
                      between local scale and catchment scale measurements and
                      modelling of gas exchange processes over land surfaces
                      (139819005)},
      pid          = {G:(DE-HGF)POF2-246 / G:(GEPRIS)139819005},
      typ          = {PUB:(DE-HGF)24},
      url          = {https://juser.fz-juelich.de/record/139214},
}