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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-597
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
02 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).
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 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 aims to assess 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 or 29.4 m). 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 5 cm show a good agreement (R2 = 0.86 and RMSE = 0.04 m3 m−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 cm and 5 cm, especially during light rainfall events.

Citation: Zhang, S., Calvet, J.-C., Darrozes, J., Roussel, N., Frappart, F., and Bouhours, G.: Deriving surface soil moisture from reflected GNSS signal observations from a grassland site in southwestern France, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-597, in review, 2017.
Sibo Zhang et al.
Sibo Zhang et al.
Sibo Zhang et al.

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Short summary
Surface soil moisture was retrieved from a grassland site in southwestern France using the GNSS-IR technique. While the vegetation biomass effect can be corrected for, the litter water interception influences the observations and cannot be easily accounted for. Positioning the antenna high up (at 29.4 m in this study) in order to observe a larger area has no significant impact on the quality of soil moisture estimates.
Surface soil moisture was retrieved from a grassland site in southwestern France using the...
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