Abstract
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 29.4 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 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 and 5 cm, especially during light rainfall events.
Highlights
Soil moisture is a key component in the hydrological cycle and in the soil–plant–atmosphere continuum
GPS L2C and L5 signal-to-noise ratio (SNR) data were obtained at a grassland site in southwestern France during a period of 15 months
A dimensionless scaled wetness index was derived from the SNR observations based on the global navigation satellite system interferometric reflectometry (GNSS-IR) technique, using indiscriminately L2C or L5 signals
Summary
Soil moisture is a key component in the hydrological cycle and in the soil–plant–atmosphere continuum. L-band satellitederived products, for example, from the Soil Moisture Active Passive (SMAP) mission or the Soil Moisture and Ocean Salinity (SMOS) mission, have a coarse resolution of tens of kilometers (Chan et al, 2016; Kerr et al, 2001). These products consist of surface volumetric soil moisture (VSM) and concern the top soil layer (from the soil surface to a depth of 1 to 5 cm). The development of new automatic monitoring techniques to measure VSM is needed
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