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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 3 | Copyright
Hydrol. Earth Syst. Sci., 22, 1931-1946, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Mar 2018

Research article | 20 Mar 2018

Deriving surface soil moisture from reflected GNSS signal observations from a grassland site in southwestern France

Sibo Zhang1,2, Jean-Christophe Calvet1, José Darrozes3, Nicolas Roussel3, Frédéric Frappart3,4, and Gilles Bouhours1 Sibo Zhang et al.
  • 1CNRM, UMR3589 (Meteo-France, CNRS), Toulouse, France
  • 2Fondation STAE, Toulouse, France
  • 3GET, UMR5563 (CNRS, Université Paul Sabatier, UR254 IRD), Toulouse, France
  • 4LEGOS, UMR5566 (CNES, CNRS, IRD, UPS), Toulouse, France

Abstract. This work assesses the estimation of surface volumetric soil moisture (VSM) using the global navigation satellite system interferometric reflectometry (GNSS-IR) technique. Year-round observations were acquired from a grassland site in southwestern France using an antenna consecutively placed at two contrasting heights above the ground surface (3.3 and 29.4m). The VSM retrievals are compared with two independent reference datasets: in situ observations of soil moisture, and numerical simulations of soil moisture and vegetation biomass from the ISBA (Interactions between Soil, Biosphere and Atmosphere) land surface model. Scaled VSM estimates can be retrieved throughout the year removing vegetation effects by the separation of growth and senescence periods and by the filtering of the GNSS-IR observations that are most affected by vegetation. Antenna height has no significant impact on the quality of VSM estimates. Comparisons between the VSM GNSS-IR retrievals and the in situ VSM observations at a depth of 5cm show good agreement (R2 = 0.86 and RMSE = 0.04m3m−3). It is shown that the signal is sensitive to the grass litter water content and that this effect triggers differences between VSM retrievals and in situ VSM observations at depths of 1 and 5cm, especially during light rainfall events.

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Short summary
Surface soil moisture was retrieved from a grassland site in southwestern France using the GNSS-IR technique. In order to efficiently limit the impact of perturbing vegetation effects, the grass growth period and the senescence period are treated separately. While the vegetation biomass effect can be corrected for, the litter water interception influences the observations and cannot be easily accounted for.
Surface soil moisture was retrieved from a grassland site in southwestern France using the...