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@ARTICLE{Jagdhuber:861588,
      author       = {Jagdhuber, Thomas and Konings, Alexandra G. and McColl,
                      Kaighin A. and Alemohammad, Seyed Hamed and Das, Narendra
                      Narayan and Montzka, Carsten and Link, Moritz and Akbar,
                      Ruzbeh and Entekhabi, Dara},
      title        = {{P}hysics-{B}ased {M}odeling of {A}ctive and {P}assive
                      {M}icrowave {C}ovariations {O}ver {V}egetated {S}urfaces},
      journal      = {IEEE transactions on geoscience and remote sensing},
      volume       = {57},
      number       = {2},
      issn         = {1558-0644},
      address      = {New York, NY},
      publisher    = {IEEE},
      reportid     = {FZJ-2019-02038},
      pages        = {788 - 802},
      year         = {2019},
      abstract     = {Active and passive low-frequency microwave measurements
                      from a number of space- and airborne instruments are used to
                      estimate soil moisture. Each of the sensing approaches has
                      distinct advantages and disadvantages. There is increasing
                      interest in combining active and passive measurements in
                      order to realize the advantages and alleviate the
                      disadvantages. In order to combine active and passive
                      measurements, their covariations with respect to soil
                      moisture need to be known. The covariation is dependent on
                      how the active and passive microwaves interact with
                      vegetation canopy and soil surface. In this paper, we
                      introduce a physics-based model for the covariation of
                      active and passive microwaves over soil surfaces with
                      vegetation cover. The analytical form for a covariation
                      function is derived which depends on the scattering and
                      absorption of microwaves by soil and vegetation with
                      different orientations, structures, and water contents. The
                      main finding is that the covariation function β is related
                      to the roughness and vegetation losses in the two
                      measurements. An increase in soil roughness or in vegetation
                      cover leads to less negative values of β, which is
                      pronounced for dense and moist vegetation. Both the soil and
                      vegetation components introduce a polarization dependence of
                      β that is caused by polarization-induced differences in
                      soil scattering and oriented plant structures. The forward
                      modeled covariations are plotted together with statistically
                      derived covariation estimates from two months of global
                      active and passive L-band observations of the Soil Moisture
                      Active Passive mission. The physically modeled and
                      statistically derived estimates of covariation are
                      comparable in magnitude and scale.},
      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:000456936500012},
      doi          = {10.1109/TGRS.2018.2860630},
      url          = {https://juser.fz-juelich.de/record/861588},
}