Time domain reflectometry (TDR) applications in Earth sciences

Time domain reflectometry (TDR) is becoming the method of choice for measurement of water content and electrical conductivity in Earth materials. New TDR devices designed specifically for measurements in porous media are cheap, robust, and amenable to automation for continuous monitoring. TDR probes are often designed for direct insertion into soil or rock using only a few conductors to minimize disturbance while providing a representative sampling volume. Permittivity measurement and interpretation is often affected by ambient conditions and media physical properties. Solid surfaces hinder the rotational freedom of water at a greater extent with increasing surface area of the porous material and are also influenced by temperature. Saline soils are electrically conductive to the point of completely attenuating the TDR signal using conventional probe designs (e.g., 15 cm length). Innovative techniques for reducing signal attenuation or otherwise preserving waveform information, thereby extending the range of permittivity measurements in lossy porous media are presented.