A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

Abstract

constant) of a material emerged as an elegant method of estimating water content in porous materials. For the Substantial advances in the measurement of water content and first time the same physical property (permittivity) could bulk soil electrical conductivity (EC) using time domain reflectometry be measured for a range of scales and used to estimate (TDR) have been made in the last two decades. The key to TDR's success is its ability to accurately measure the permittivity of a material water content. Electromagnetic methods, whether TDR and the fact that there is a good relationship between the permittivity (localized measurement), ground penetrating radar of a material and its water content. A further advantage is the ability (two-dimensional profile), or active microwave remote to estimate water content and measure bulk soil EC simultaneously sensing (land surface), all estimate water content based using TDR. The aim of this review is to summarize and examine on the permittivity of the target medium. A further advances that have been made in terms of measuring permittivity and advance was the development of analysis methods using bulk EC. The review examines issues such as the effective frequency TDR. Time domain reflectometry was adapted to estiof the TDR measurement and waveform analysis in dispersive dielecmate both soil water content (Hoekstra and Delaney, trics. The growing importance of both waveform simulation and in-1974; Topp et al., 1980) and soil bulk EC simultaneously verse analysis of waveforms is highlighted. Such methods hold great (Dalton et al., 1984). In spite of decades of research, potential for obtaining far more information from TDR waveform analysis. Probe design is considered in some detail and practical guid-we are only beginning to efficiently utilize electrical ance is given for probe construction. The importance of TDR measuretechnology that ranges from satellite and airborne radar ment sampling volume is considered and the relative energy storage to ground penetrating radar and localized sensors such density is modeled for a range of probe designs. Tables are provided as TDR and impedance probes. that compare some of the different aspects of commercial TDR equip-The underlying success of these techniques can be ment, and the units are discussed in terms of their performance and considered in two parts, the first of which is the equiptheir advantages and disadvantages. It is hoped that the review will ment's ability to accurately measure the bulk dielectric provide an informative guide to the more technical aspects of permitpermittivity and EC of a material. The second is the close tivity and EC measurement using TDR for the novice and expert alike.relationship between the measured permittivity and the volumetric water content, or the ionic concentration and the bulk EC of the material. This review concentrates

Effect of Water Stress and Fungal Inoculation on Monoterpene Emission from an Historical and a New Pine Host of the Mountain Pine Beetle

“…We measured the apparent dielectric constant of the soil with a Tektronix 1502B (Beaverton, OR, USA) and used the empirical equation for organic soils in Robinson et al (2003) to relate it to water content. Rate of photosynthesis and stomatal conductance were measured using a LI-6400 (LI-COR Biosciences, Lincoln, NE, USA).…”

Soil Moisture & Snow Properties Determination with GNSS in Alpine Environments: Challenges, Status, and Perspectives

“…The method is relatively insensitive to soil density, temperature, and salinity, and only mildly disturbs the sample by the insertion of the probe. Accuracy is in the order of 1 to 2% [54]. Therefore, it has found widespread use in hydrological research and agricultural applications.…”

“…Equipment is commercially available and usually measures within small volumes in the order of 5 cm 3 . Extensive reviews of TDR applied to soil moisture determination can be found in [55] and [54]. Frequency domain reflectometry (FDR) uses the same principle as TDR, but analyzes the reflected waveform in the frequency domain, enabling the determination of frequency dependent complex dielectric permittivity [56].…”

Electrical conductivity of soil irrigated with swine wastewater estimated by time-domain reflectometry¹

“…According to Embrapa (1997), the usual saturation-extract method for evaluating soil salinity is time and space-limited since its results represent the soil conditions at the sampling moment and for the tested soil volume. Time-domain reflectometry (TDR) may be a suitable procedure for the indirect determination of apparent soil electrical conductivity (EC soil ) under field conditions, not only in view of the real time readings but also of the minimal disturbance of the soil structure (Robinson et al, 2003;Nadler, 2004;Coelho et al, 2005;Souza et al, 2006). However, TDR devices must be calibrated to the specific characteristics of each soil (Hamed et al, 2003), by collecting equipment data and reference values and relating them (Cichota, 2003).…”