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Vadose Zone Journal Abstract - Original Research

Soil Hydraulic Parameters and Surface Soil Moisture of a Tilled Bare Soil Plot Inversely Derived from L-Band Brightness Temperatures

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This article in VZJ

  1. Vol. 13 No. 1
     
    Received: Apr 23, 2013
    Published: January 13, 2014


    * Corresponding author(s): j.vanderborght@fz-juelich.de
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doi:10.2136/vzj2013.04.0075
  1. M. Dimitrova,
  2. J. Vanderborght a,
  3. K. G. Kostovb,
  4. K. Z. Jadoonac,
  5. L. Weihermüllera,
  6. T. J. Jacksond,
  7. R. Bindlishd,
  8. Y. Pachepskye,
  9. M. Schwankf and
  10. H. Vereeckena
  1. a Research Centre Jülich, Institute of Bio- and Geosciences: Agrosphere (IBG 3), Jülich 52425, Germany
    b Bulgarian Academy of Sciences, Institute of Electronics, Sofia 1784, Bulgaria
    c Water Desalination and Reuse Center, King Abdullah Univ. of Science and Technology, Thuwal 23955-6900, Saudi Arabia
    d USDA-ARS, Hydrology and Remote Sensing Lab., Beltsville, MD 20705-2350
    e USDA-ARS, Environmental Microbial and Food Safety Lab., Beltsville, MD 20705-2350
    f Swiss Federal Institute WSL, Mountain Hydrology and Torrents, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland, and Gamma Remote Sensing AG, Worbstrasse 225, 3073 Gümligen, Switzerland.

Abstract

L-band radiometers can be used to remotely monitor the microwave brightness temperature of land surfaces. We investigated how soil hydraulic properties and soil moisture contents of a bare soil plot can be inferred from L-band brightness temperatures using a coupled inversion approach.

We coupled a radiative transfer model and a soil hydrologic model (HYDRUS 1D) with an optimization routine to derive soil hydraulic parameters, surface roughness, and soil moisture of a tilled bare soil plot using measured brightness temperatures at 1.4 GHz (L-band), rainfall, and potential soil evaporation. The robustness of the approach was evaluated using five 28-d data sets representing different meteorological conditions. We considered two soil hydraulic property models: the unimodal Mualem–van Genuchten and the bimodal model of Durner. Microwave radiative transfer was modeled by three different approaches: the Fresnel equation with depth-averaged dielectric permittivity of either 2- or 5-cm-thick surface layers and a coherent radiative transfer model (CRTM) that accounts for vertical gradients in dielectric permittivity. Brightness temperatures simulated by the CRTM and the 2-cm-layer Fresnel model fitted well to the measured ones. L-band brightness temperatures are therefore related to the dielectric permittivity and soil moisture in a 2-cm-thick surface layer. The surface roughness parameter that was derived from brightness temperatures using inverse modeling was similar to direct estimates from laser profiler measurements. The laboratory-derived water retention curve was bimodal and could be retrieved consistently for the different periods from brightness temperatures using inverse modeling. A unimodal soil hydraulic property function underestimated the hydraulic conductivity near saturation. Surface soil moisture contents simulated using retrieved soil hydraulic parameters were compared with in situ measurements. Depth-specific calibration relations were essential to derive soil moisture from near-surface installed sensors.

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Copyright © 2014. Copyright © by the Soil Science Society of America, Inc.