DEVELOPMENT AND APPLICATIONS OF TDR INVERSION ALGORITHMS WITH HIGH SPATIAL RESOLUTION FOR MOISTURE PROFILE DETERMINATION

Many applications in hydrology, agriculture and civil engineering ask for the moisture profile in soils or building constructions. So far TDR technology was limited to integral or very coarse resolved water content determination along the transmission line. A new reconstruction algorithm has been developed which uses the full information content of the TDR signal for two-sided reflection data for one round trip. It is based on the telegraph equation for nonuniform transmission lines and an optimization approach to reconstruct simultaneously two line parameters with high spatial resolution. These two parameters are converted to dielectric coefficients respectively water content by the help of a cable model and dielectric mixing rules. An experimental set-up demonstrates how the reconstruction algorithm works with real data. Field investigations on a natural-scaled levee model were performed as well. Here the levee model was equipped with 12 vertical installed transmission lines between 0.7 and 3.0 meters along a cross-section. A permanent monitoring of transient hydrological processes e.g. the infiltration into the levee by meteorological influences or the percolation due to simulated flood events could be realized for the first time.

Stefan Schlaeger
Environmental Research Center
University of Karlsruhe

Alexander Scheuermann
Institute for Soil Mechanics and Rock Mechanics,
University of Karlsruhe

Christof Hübner
Institute for Meteorology and Climatology,
Karlsruhe Research Center - Technology and Environment,