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

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