Electromagnetic determination of soil water content: Measurements in coaxial transmission lines
TL;DR: The dependence of the dielectric constant, at frequencies between 1 MHz and 1 GHz, on the volumetric water content is determined empirically in the laboratory as discussed by the authors, and the effect of varying the texture, bulk density, temperature, and soluble salt content on this relationship was also determined.
Abstract: The dependence of the dielectric constant, at frequencies between 1 MHz and 1 GHz, on the volumetric water content is determined empirically in the laboratory. The effect of varying the texture, bulk density, temperature, and soluble salt content on this relationship was also determined. Time-domain reflectometry (TDR) was used to measure the dielectric constant of a wide range of granular specimens placed in a coaxial transmission line. The water or salt solution was cycled continuously to or from the specimen, with minimal disturbance, through porous disks placed along the sides of the coaxial tube.
Four mineral soils with a range of texture from sandy loam to clay were tested. An empirical relationship between the apparent dielectric constant Ka and the volumetric water content θv, which is independent of soil type, soil density, soil temperature, and soluble salt content, can be used to determine θv, from air dry to water saturated, with an error of estimate of 0.013. Precision of θv to within ±0.01 from Ka can be obtained with a calibration for the particular granular material of interest. An organic soil, vermiculite, and two sizes of glass beads were also tested successfully. The empirical relationship determined here agrees very well with other experimenters' results, which use a wide range of electrical techniques over the frequency range of 20 MHz and 1 GHz and widely varying soil types. The results of applying the TDR technique on parallel transmission lines in the field to measure θv versus depth are encouraging.
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01 Jan 2011TL;DR: In this article, the authors present basic tools for elasticity and Hooke's law, effective media, granular media, flow and diffusion, and fluid effects on wave propagation for wave propagation.
Abstract: Preface 1. Basic tools 2. Elasticity and Hooke's law 3. Seismic wave propagation 4. Effective media 5. Granular media 6. Fluid effects on wave propagation 7. Empirical relations 8. Flow and diffusion 9. Electrical properties Appendices.
2,007 citations
TL;DR: In this article, the basic principles and practices involved in acquiring high-quality radar data in the field are illustrated by selected case histories, showing how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m.
Abstract: Ground-penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions. The need to better understanding overburden conditions for activities such as geochemical sampling, geotechnical investigations, and placer exploration, as well as the factors controlling groundwater flow, has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible. The areas of application for ground-penetrating radar are diverse. The method has been used successfully to map ice thickness, water depth in lakes, bedrock depth, soil stratigraphy, and water table depth. It is also used to delineate rock fabric, detect voids and identify karst features. The effective application of the radar for the high-resolution definition of soil stratigraphy and fractures in bedrock is highlighted. The basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories. One example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m. Two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine. Another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination. The corroboration of the radar results by borehole investigations demonstrates the power and utility of the high-resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes. With the advent of new instrumentation and field procedures, the routine application of the radar method is becoming economically viable and the method will see expanded use in the future.
1,962 citations
09 Jan 2020
TL;DR: The third edition of the reference book as discussed by the authors has been thoroughly updated while retaining its comprehensive coverage of the fundamental theory, concepts, and laboratory results, and highlights applications in unconventional reservoirs, including water, hydrocarbons, gases, minerals, rocks, ice, magma and methane hydrates.
Abstract: Responding to the latest developments in rock physics research, this popular reference book has been thoroughly updated while retaining its comprehensive coverage of the fundamental theory, concepts, and laboratory results. It brings together the vast literature from the field to address the relationships between geophysical observations and the underlying physical properties of Earth materials - including water, hydrocarbons, gases, minerals, rocks, ice, magma and methane hydrates. This third edition includes expanded coverage of topics such as effective medium models, viscoelasticity, attenuation, anisotropy, electrical-elastic cross relations, and highlights applications in unconventional reservoirs. Appendices have been enhanced with new materials and properties, while worked examples (supplemented by online datasets and MATLAB® codes) enable readers to implement the workflows and models in practice. This significantly revised edition will continue to be the go-to reference for students and researchers interested in rock physics, near-surface geophysics, seismology, and professionals in the oil and gas industries.
1,387 citations
TL;DR: In this article, the authors estimate that half of the closed forests of Brazilian Amazonia depend on deep root systems to maintain green canopies during the dry season, and as much as 15% of this deep-soil carbon turns over on annual or decadal timescales.
Abstract: DEFORESTATION and logging transform more forest in eastern and southern Amazonia than in any other region of the world1–3. This forest alteration affects regional hydrology4–11 and the global carbon cycle12–14, but current analyses of these effects neglect an important deep-soil link between the water and carbon cycles. Using rainfall data, satellite imagery and field studies, we estimate here that half of the closed forests of Brazilian Amazonia depend on deep root systems to maintain green canopies during the dry season. Evergreen forests in northeastern Para state maintain evapotranspiration during five-month dry periods by absorbing water from the soil to depths of more than 8m. In contrast, although the degraded pastures of this region also contain deep-rooted woody plants, most pasture plants substantially reduce their leaf canopy in response to seasonal drought, thus reducing dry-season evapotranspiration and increasing potential subsurface runoff relative to the forests they replace. Deep roots that extract water also provide carbon to the soil. The forest soil below 1 m depth contains more carbon than does above-ground biomass, and as much as 15% of this deep-soil carbon turns over on annual or decadal timescales. Thus, forest alteration that affects depth distributions of carbon inputs from roots may also affect net carbon storage in the soil.
1,288 citations
TL;DR: A ground-penetrating radar (GPR) is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface as mentioned in this paper, which can be used to detect electrical faults.
963 citations
References
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TL;DR: In this paper, a simple empirical model was proposed to describe the dielectric behavior of the soil-water mixtures and the model employed the mixing of either the Dielectric constants or the refraction indices of ice, water, rock and air, and treated the transition moisture value as an adjustable parameter.
Abstract: The recent measurements on the dielectric properties of soils have shown that the variation of dielectric constant with moisture content depends on soil types. The observed dielectric constant increases only slowly with moisture content up to a transition point. Beyond the transition it increases rapidly with moisture content. The moisture value at transition region was found to be higher for high clay content soils than for sandy soils. Many mixing formulas reported in the literature were compared with, and were found incompatible with, the measured dielectric variations of soil-water mixtures. A simple empirical model was proposed to describe the dielectric behavior of the soil-water mixtures. This model employs the mixing of either the dielectric constants or the refraction indices of ice, water, rock, and air, and treats the transition moisture value as an adjustable parameter. The calculated mixture dielectric constants from the model were found to be in reasonable agreement with the measured results over the entire moisture range of 0-0.5 cm3/cm3. The transition moistures derived from the model range from 0.16 to 0.33 and are strongly correlated with the wilting points of the soils estimated from their textures. This relationship between transition moisture and wilting point provides a means of estimating soil dielectric properties on the basis of texture information.
984 citations
TL;DR: In this article, the complex dielectric constant of four soils, including a sand, a silt, and two clays, was measured over the frequency range from 0.1 × 109 Hz to 26 ×109 Hz.
Abstract: The complex dielectric constant of four soils, including a sand, a silt, and two clays, was measured over the frequency range from 0.1 × 109 Hz to 26 × 109 Hz. The water content of the soils was varied from 0.0 g H2O/g soil to 0.15 g H2O/g soil, and the temperature from 24°C to 20°C. The dielectric relaxation spectrum of water in soils was found to be displaced to lower frequencies than the dielectric relaxation spectrum of water in bulk. The results showed that the relation between volumetric water content and the complex dielectric constant is relatively independent of soil type. At temperatures above freezing the complex dielectric constant of water in soils, at the water contents investigated, decreases with temperature, a type of behavior normally found only in solids. Below the freezing point the phase composition of water in soils determines the temperature dependence of the complex dielectric constant.
417 citations
332 citations
01 Jan 1974
TL;DR: In this article, the conductivity and dielectric constants of gray clay and a reddish-brown clay loam were determined as a function of soil density, soil moisture, and excitation frequency.
Abstract: Measurements are made to determine the conductivity and dielectric constants of a gray clay loam and a reddish-brown clay loam. The measurements are made as a function of soil density (from 1.2 g/cm3to 1.8 g/cm3), soil moisture (from 0 percent to 20 percent of the dry soil weight), and excitation frequency (from 30 MHz to 4 GHz), using standard transmission line techniques. A correction term is presented to allow the effective open-circuit and short-circuit connections to be placed at any convenient location with respect to the soil-air interface.
283 citations
TL;DR: In this article, a model of soil composed of a multiphase mixture of solid particles, water, and air voids is proposed from which the complex permittivity, or dielectric constant and conductivity, is calculated.
Abstract: A model of soil composed of a multiphase mixture of solid particles, water, and air voids is proposed from which the complex permittivity, or dielectric constant and conductivity, is calculated. It is based on the Hanai/Bruggelman/Wagner theory of mixtures and considers the ionic conducting water as partly dispersed and partly the dispersing medium, an important distinction with this theory. The permittivity as a function of frequency and water content is predicted. The increase in dielectric constant with water volume fraction does not differ greatly with soil type in the high-frequency limit and is approximated by a normal curve specified by the theory. A normal curve and the marked increase in dielectric constant at lower frequencies has been observed experimentally. It is concluded that this semidisperse theory of the dielectric permittivity is successful in describing the behavior of soils containing moisture in the high-frequency range (1 MHz-1 GHz). Approximations to the more detailed theory and a series-parallel RC equivalent circuit are given.
113 citations