High-resolution space–time quantification of soil moisture along a hillslope using joint analysis of ground penetrating radar and frequency domain reflectometry data

Abstract

We combined ground-penetrating radar (GPR) and frequency domain reflectometry (FDR) to assess the space–time variability of soil moisture along a hillslope. Time-lapse GPR and FDR measurements were conducted weekly during the period 23/03–08/06/2011 along a cultivated hillslope in the Belgian loam belt. A full-wave GPR model, a soil dielectric mixing model and the Debye equation were combined to directly estimate soil moisture from GPR measurements. Measured GPR data were well reproduced by the full-wave GPR model, resulting in a relatively good agreement between the GPR and FDR-derived soil moisture. Subsequently, we merged the soil moisture obtained from both techniques in a data fusion framework and we investigated its spatial and temporal variability. The results indicate that there was a high correlation between the spatial variability of soil moisture and topography as well as between its temporal variability and rainfall. A temporal stability analysis showed that soil moisture at the footslope is higher and more stable than that at the summits and backslopes. The proposed approach appears to be promising for assessing soil moisture at the hillslope scale with a relatively high space–time resolution.