TDR SIGNAL MODELLING USING THE ELECTRIC LINE APPROACH : MODEL VALIDATION AND SIGNAL INVERSION TO RETRIEVE SOIL MOISTURE PROFILE

The TDR signal propagation is represented using the electric line approach. The telegraphist equations are resolved in the time domain using a finite element method. The media heterogeneities along the line can be accounted for by distributing the electric properties spatially. The computation gives the temporal evolution of the electric intensity and tension at every location of the line. The TDR signal is extracted from the tension at the entrance end of the line. Then, the simulated signals were compared to measurements made in artificial media (using a multi compartment tank with various well known dielectric media) and in real field conditions. Simulations are in good agreement with measurements but requires to fit the dielectric loss. A discussion is presented on the obtained fitted values and on the possibilities to handle this term in operational application. An inversion procedure of the model is proposed to retrieve soil moisture profiles. Discussion is proposed on the expected accuracy in relation to the TDR technical characteristics as well as to the soil moisture conditions.

Chambarel, A. & Ferry, E. : LHC, Université d'Avignon, France
Chanzy, A. : INRA, Unité de science du sol, Avignon, France
Laurent, J. -P. : LTHE/CNRS, Grenoble, France
Todoroff, P. : CIRAD, Montpellier, France
Ferrari, P. : Université de Chambéry, Chambéry, France