Calculation of in situ soil water content profiles from TDR signal traces

The authors present a numerical one-dimensional model which computes the soil water content profile, along transmission line probes, from time-domain reflectometry signal traces recorded with a reflectometer (TDR). Taking a discrete time-domain approach, they first developed a direct iterative model which computes simulated signal traces from the dielectric constant distribution of the propagation medium. The results tallied well with signal traces recorded in simple cases. The inverse model was developed in a second stage, to compute water content distribution along the transmission line probes from a reflected signal trace. The results are shown both for controlled media and field conditions and are compared to direct water content measurements. Filtering of the reflection coefficients had to be incorporated to compensate for the high sensitivity to noise of the iterative computation and the simplicity of the propagation hypothesis. The inverted profiles are very close to the direct measurements, validating this model for measurements in low loss soils.