Measurement of electrical conductivity by Time Domain Reflectometry: Materiel effects on main used models
A. Rochdi1*, M. Vanclooster2, M Elgharous3
1Département de Géologie Appliquée, Université Hassan 1er, FST, B.P. 577, 26000 Settat, Morocco
2Department of Environmental Sciences and Land Use Planning, UCL,
Place Croix du Sud 2, Boite 2, B-1348 Louvain-la-Neuve, Belgium
3CRRA, INRA, B.P. 589, 26000 Settat, Morocco
* Corresponding author. E-mail:firstname.lastname@example.org
Received : 15 February 2003 ; revised version accepted : 01 June 2003
Time domain reflectometry (TDR) based electrical conductivity measurements (sa-TDR) have been compared with the low frequency geophysical prospecting based electrical conductivity measurements (sa-FEGP). Experiments were carried out on different specific solutions and three artificially controlled porous media (glass beads, sand and loamy soil). The experiments allowed to elucidate the impact of material properties on sa inferences from TDR measurements and to evaluate the performance of different sa calibration models in terms of the material properties. It was shown that the use of a characteristic impedance derived from TDR probe calibrations in solutions of known permittivity is more adequate to estimate s a, than the use of characteristic impedance derived from probe geometry calculations. Further it was shown that material properties might affect sa estimates from TDR measurements considerably which could be attributed to losses related to the water. The TDR method has the ability to measure soil water content and bulk electrical conductivity in the same sampling volume, but the two obtained soil variables are not truly independent. Beside the material properties of the porous medium sa-TDR values seem to be governed by water content.
Keywords : TDR, electrical conductivity, permittivity, impedance, dielectric losses, porous media, soil.