ABSTRACT
Many applications in geotechnical engineering, hydrology and agriculture require determining the transient water content profile characterizing soil hydraulic processes in unsaturated soils. However the monitoring of a sufficient number of soil moisture profiles can be costly, laborious and extraordinary invasive, especially if the profiles are determined point-wise by a large amount of single probes buried in soil. A recently developed reconstruction algorithm (Schlaeger 2005) allows computing complete soil water content profiles along elongated single moisture probes from time domain reflectometer (TDR) measurements in a short time. This method leads to a reduction of the number of probes accompanied by a higher spatial resolution of moisture profiles. The whole technology of soil moisture profile retrieval-including measurement devices and probes, reconstruction algorithm and calibration procedure-has been named Spatial TDR (Becker 2004, Huebner et al. 2005). This method is being developed and applied by the Soil Moisture Group (SMG),
an interdisciplinary research group at the University of Karlsruhe. This article gives a brief introduction into the fundamentals of TDR before the basic concept of STDR is explained with the emphasis on its algorithm and the initial probe calibration by way of a coated 3-rod-probe. The theoretical accuracy of the measured moisture profiles is assessed by means of electromagnetic (EM) field simulations. Laboratory and large-scale experiments were realized to evaluate the method and to compare the reconstructed water content profiles with comparable information of the real soil.
