ON THE USE OF THE TDR TRIME-TUBE SYSTEM FOR PROFILING WATER CONTENT IN SOILS

The TDR TRIME-tube system designed and manufactured by the German company IMKO  consists in a polymer access tube inserted in the soil in which a cylindrical 18 cm long TDR probe is successively leveled at different depths to determine the surrounding soil water-content profile. The use of this system is particularly straightforward because all the TDR measurement  parameters are  automatically recognized by the electronics when the probe is plugged in and because the results are directly displayed in terms of water-contents using an inner calibration. As a group of French users, our purpose was to evaluate the TRIME performances compared to the gravimetric and neutron probe techniques classically used in soil physics. Five sites have been equipped with polymer access tubes and water-content profiles monitored over long periods under highly differing conditions. In a first level of analysis, water-content profiles and resulting water storage evolutions have been compared. We found situations in which the TDR tube probe provides good realistic measurements unless, in some other cases, we have to face, either strong non-physical deviations from the assumed "true" water-contents  or, even impossibilities to get  water-content values. Hence, in an second step, we tried to explain and correct these misbehaviors working in thee main directions : i) visualization and interpretation of the signal delivered by this probe ; ii) modeling of the composite dielectric constant measurement done by such a system ; iii) development of calibration strategies and procedures. The main issues of this work will be presented in this communication.

J.P. Laurent & J.L. Thony
LTHE
France

N. Breda
INRA, Ecophysiologie Forestière
France

C. Chanzy
|INRA, Unité de Science du Sol
France

C. Chevallier
INRA, Domaine INRA SAD
France

P. Ruelle
CEMAGREF
France