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@ARTICLE{Meyer:856440,
      author       = {Meyer, Thomas and Weihermüller, Lutz and Vereecken, Harry
                      and Jonard, François},
      title        = {{V}egetation {O}ptical {D}epth and {S}oil {M}oisture
                      {R}etrieved from {L}-{B}and {R}adiometry over the {G}rowth
                      {C}ycle of a {W}inter {W}heat},
      journal      = {Remote sensing},
      volume       = {10},
      number       = {10},
      issn         = {2072-4292},
      address      = {Basel},
      publisher    = {MDPI},
      reportid     = {FZJ-2018-05839},
      pages        = {1637 -},
      year         = {2018},
      abstract     = {L-band radiometer measurements were performed at the
                      Selhausen remote sensing field laboratory (Germany) over the
                      entire growing season of a winter wheat stand. L-band
                      microwave observations were collected over two different
                      footprints within a homogenous winter wheat stand in order
                      to disentangle the emissions originating from the soil and
                      from the vegetation. Based on brightness temperature (TB)
                      measurements performed over an area consisting of a soil
                      surface covered by a reflector (i.e., to block the radiation
                      from the soil surface), vegetation optical depth (τ)
                      information was retrieved using the tau-omega (τ-ω)
                      radiative transfer model. The retrieved τ appeared to be
                      clearly polarization dependent, with lower values for
                      horizontal (H) and higher values for vertical (V)
                      polarization. Additionally, a strong dependency of τ on
                      incidence angle for the V polarization was observed.
                      Furthermore, τ indicated a bell-shaped temporal evolution,
                      with lowest values during the tillering and senescence
                      stages, and highest values during flowering of the wheat
                      plants. The latter corresponded to the highest amounts of
                      vegetation water content (VWC) and largest leaf area index
                      (LAI). To show that the time, polarization, and angle
                      dependence is also highly dependent on the observed
                      vegetation species, white mustard was grown during a short
                      experiment, and radiometer measurements were performed using
                      the same experimental setup. These results showed that the
                      mustard canopy is more isotropic compared to the wheat
                      vegetation (i.e., the τ parameter is less dependent on
                      incidence angle and polarization). In a next step, the
                      relationship between τ and in situ measured vegetation
                      properties (VWC, LAI, total of aboveground vegetation
                      biomass, and vegetation height) was investigated, showing a
                      strong correlation between τ over the entire growing season
                      and the VWC as well as between τ and LAI. Finally, the soil
                      moisture was retrieved from TB observations over a second
                      plot without a reflector on the ground. The retrievals were
                      significantly improved compared to in situ measurements by
                      using the time, polarization, and angle dependent τ as a
                      priori information. This improvement can be explained by the
                      better representation of the vegetation layer effect on the
                      measured TB},
      cin          = {IBG-3},
      ddc          = {620},
      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:000448555800137},
      doi          = {10.3390/rs10101637},
      url          = {https://juser.fz-juelich.de/record/856440},
}