Dielectric relaxation behavior of Callovo-Oxfordian clay rock: A hydraulic-mechanical-electromagnetic coupling approach

Water content is a key parameter to monitor in nuclear waste repositories such as the planed underground repository in Bure, France, in the Callovo-Oxfordian (COx) clay formation. High-frequency electromagnetic (HF-EM) measurement techniques, i.e., time or frequency domain reflectometry, offer useful tools for quantitative estimation of water content in porous media. However, despite the efficiency of HF-EM methods, the relationship between water content and dielectric material properties needs to be characterized. Moreover, the high amount of swelling clay in the COx clay leads to dielectric relaxation effects which induce strong dispersion coupled with high absorption of EM waves. Against this background, the dielectric relaxation behavior of the clay rock was studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. For this purpose, undisturbed and disturbed clay rock samples were conditioned to achieve a water saturation range from 0.16 to nearly saturation. The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high-frequency water process and two interface processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell-Wagner effects). The frequency-dependent HF-EM properties were further modeled based on a novel hydraulic-mechanical-electromagnetic coupling approach developed for soils. The results show the potential of HF-EM techniques for quantitative monitoring of the hydraulic state in underground repositories in clay formations

Dielectric relaxation behavior of Callovo-Oxfordian clay rock: A hydraulic-mechanical-electromagnetic coupling approach

Water content is a key parameter to monitor in nuclear waste repositories such as the planed underground repository in Bure, France, in the Callovo-Oxfordian (COx) clay formation. High-frequency electromagnetic (HF-EM) measurement techniques, i.e., time or frequency domain reflectometry, offer useful tools for quantitative estimation of water content in porous media. However, despite the efficiency of HF-EM methods, the relationship between water content and dielectric material properties needs to be characterized. Moreover, the high amount of swelling clay in the COx clay leads to dielectric relaxation effects which induce strong dispersion coupled with high absorption of EM waves. Against this background, the dielectric relaxation behavior of the clay rock was studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. For this purpose, undisturbed and disturbed clay rock samples were conditioned to achieve a water saturation range from 0.16 to nearly saturation. The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high-frequency water process and two interface processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell-Wagner effects). The frequency-dependent HF-EM properties were further modeled based on a novel hydraulic-mechanical-electromagnetic coupling approach developed for soils. The results show the potential of HF-EM techniques for quantitative monitoring of the hydraulic state in underground repositories in clay formations. Key Points Dielectric relaxation behavior of porous mediaRadio and microwave remote sensing techniquesHydraulic-mechanical-electromagnetic couplin

EFFECT OF SALINITY ON THE DIELECTRIC PROPERTIES OF GEOLOGICAL MATERIALS : IMPLICATION FOR SOIL MOISTURE DETECTION BY MEANS OF REMOTE SENSING

International audienceThis paper deals with the exploitation of dielectric properties of saline deposits for the detection and mapping of moisture in arid regions on both Earth and Mars. We then present a simulation and experimental study in order to assess the effect of salinity on the permittivity of geological materials and therefore on the radar backscattering coefficient in the [1-7GHz] frequency range. Dielectric mixing models were first calibrated by means of experimental measurements before being used as input parameters of analytical scattering models (IEM, SPM). Simulation results will finally be compared to field measurements (Pyla dune, Death Valley, Mojave Desert) and will be used for the interpretation of SAR data (AIRSAR, PALSAR)

Soil textural effects on radar response to soil moisture

There are no author-identified significant results in this report

Survey of methods for soil moisture determination

Existing and proposed methods for soil moisture determination are discussed. These include: (1) in situ investigations including gravimetric, nuclear, and electromagnetic techniques; (2) remote sensing approaches that use the reflected solar, thermal infrared, and microwave portions of the electromagnetic spectrum; and (3) soil physics models that track the behavior of water in the soil in response to meteorological inputs (precipitation) and demands (evapotranspiration). The capacities of these approaches to satisfy various user needs for soil moisture information vary from application to application, but a conceptual scheme for merging these approaches into integrated systems to provide soil moisture information is proposed that has the potential for meeting various application requirements

Imaging of buried utilities by ultra wideband sensory systems

Third-party damage to the buried infrastructure like natural gas pipelines, water distribution pipelines and fiber optic cables are estimated at $10 billion annually across the US. Also, the needed investment in upgrading our water and wastewater infrastructure over the next 20 years is estimated by Environmental Protection Agency (EPA) at$400 billion, however, non-destructive condition assessment technologies capable of providing quantifiable data regarding the structural integrity of our buried assets in a cost-effective manner are lacking. Both of these areas were recently identified several U.S. federal agencies as \u27critical national need\u27. In this research ultra wideband (UWB) time-domain radar technology was adopted in the development of sensory systems for the imaging of buried utilities, with focus on two key applications. The first was the development of a sensory system for damage avoidance of buried pipes and conduits during excavations. A sensory system which can be accommodated within common excavator buckets was designed, fabricated and subjected to laboratory and full-scale testing. The sensor is located at the cutting edge (teeth), detecting the presence of buried utilities ahead of the cutting teeth. That information can be used to alert the operator in real-time, thus avoiding damage to the buried utility. The second application focused on a sensory system that is capable of detecting structural defects within the wall of buried structures as well as voids in the soil-envelope encasing the structure. This ultra wideband sensory system is designed to be mounted on the robotic transporter that travels within the pipeline while collecting data around the entire circumference. The proposed approach was validated via 3-D numerical simulation as well as full-scale experimental testing

Microwave forward model for land surface remote sensing

In order to improve hydro-meteorological model prediction using remote-sensing measurements the difference between the model world and the observed world should be identified. The forward model proposed in this study allows us to simulate the BT (brightness temperature) from the land surface model to compare with the observed microwave BT. The proposed dielectric mixing model is the key part of the forward model to properly link the model parameters and the BT observed by remote sensing. In this study, it was established that the physically valid computation of the effective dielectric constant should be based on the arithmetic average with consideration of the proposed universal damping factor. This physically based dielectric mixing model is superior to the refractive mixing model or semi-empirical/calibration model with RMSE values of 0.96 and 0.63 for the predicted real and imaginary parts, respectively, compared to the measured values. The RMSE obtained with the new model is smaller than those obtained by other researchers using refractive mixing models for operational microwave remote sensing. Once we determine the model uncertainty using this forward model, we can update the model state using the values obtained from the remote-sensing measurement. The challenging task in this process is to resolve the ill-posed inversion problem (estimation of multiple model parameters from a single BT measurement). This study proposes a simple partitioning factor based on model physics. Again, the forward model is crucial because these factors are required to be computed in BT space. In the case study involving the Schäfertal catchment area, the proposed forward model, including the new dielectric mixing model, and the proper partitioning factors computed from land surface model physics was able to successfully extract the refined soil texture information from the microwave BT measurements. The highly resolved soil moisture variability based on the refined soil texture will allow us to predict convective precipitation with higher spatial and temporal accuracy in the numerical weather forecasting model. Moreover, microwave remote sensing using the developed forward model, which provides the soil texture, soil moisture, and soil temperature with a fine scale resolution, is expected to open up new possibilities to examine the energy balance closure problem with unprecedented realism.Zur Verbesserung der Vorhersagen von hydrometeorologischen Modellen unter Verwendung von Fernerkundungsmessungen muss der Unterschied zwischen der Modellwelt und den Messdaten identifiziert werden. Das in dieser Studie vorgeschlagene Vorwärtsmodell erlaubt es uns, Strahlungstemperaturen (BT) mit einem Landoberflächenmodell zu simulieren und mit gemessenen Mikrowellen-BT-Werten zu vergleichen. Ein neues dielektrisches Mischungsmodell wird vorgeschlagen, das den entscheidenden Teil des Vorwärtsmodells ausmacht, der die Modellparameter und die durch Fernerkundung gemessene BT richtig verbindet. In dieser Studie wurde festgestellt, dass die physikalisch fundierte Berechnung der effektiven Dielektrizitätskonstante auf dem arithmetischen Mittelwert unter Berücksichtigung eines ebenfalls neu vorgeschlagenen universalen Dämpfungsfaktors basieren sollte. Dieses auf den Regeln der Physik basierende dielektrische Mischungsmodell ist dem Brechungsindexmischungsmodell oder dem semi-empirischen Kalibrierungsmodell überlegen wie RMSE-Werte von 0,96 und 0,63 für den Vergleich der vorhergesagten realen bzw. imaginären Teile mit den gemessenen Werten zeigen. Der mit dem neuen Modell erhaltene RMSE ist kleiner als derjenige, den man mit den in der operationalen Mikrowellenfernerkundung verwendeten Brechungsindexmischungsmodellen erhält. Nach der Quantifizierung der Modellunsicherheit mithilfe des neuen Vorwärtsmodells kann der Modellzustand mithilfe der mittels Fernerkundung gemessenen Werte verbessert werden. Die Herausforderung in diesem Prozess ist es, das schlecht gestellte Inversionsproblem zu lösen (Ableitung mehrerer Modellparameter aus einer BT-Messung). Diese Studie schlägt einen einfachen Partitionierungsfaktor auf Basis der Modellphysik vor. Auch hier ist das Vorwärtsmodell entscheidend, da diese Faktoren im BT-Raum berechnet werden müssen. In einer Fallstudie im Schäfertal-Einzugsgebiet konnte das vorgeschlagene Vorwärtsmodell, einschließlich des neuen dielektrischen Mischungsmodells und der richtigen Partitionierungsfaktoren berechnet aus der Landoberflächenmodellphysik, erfolgreich verfeinerte Bodentexturinformationen aus den Mikrowellen-BT-Messungen extrahieren. Die hochaufgelöste Bodenfeuchtevariabilität basierend auf der verfeinerten Bodentextur wird es erlauben, konvektiven Niederschlag in numerischen Wettervorhersagemodellen mit höherer räumlicher und zeitlicher Genauigkeit zu prognostizieren. Darüberhinaus wird erwartet, dass die Mikrowellenfernerkundung mit dem entwickelten Vorwärtsmodell, das Bodentextur, Bodenfeuchte und Bodentemperatur in hoher Auflösung liefert, neue Möglichkeiten eröffnet, das Problem der Energiebilanzschließung mit bisher nicht erreichter Detailtreue zu untersuchen

Study on the remediation of organic soil contaminated with polychlorinated biphenyls using a variable frequency microwave furnace

The development of new and innovative remediation technologies for soil contaminated with Polychlorinated Biphenyl (PCB) is necessary to fulfill the need of cleanup of contaminated sites. In the past eight years the Laboratory for Microwave treatment as Hazardous Substance Management Research Center has investigated the use of Microwave energy to remediate contaminated soils. A major drawback of using single frequencies of the microwave range is the non-uniformity of the electromagnetic field. In this thesis a Variable Frequency Microwave Furnace (operating between 2.40 and 7.50 GHz) is used to improve the uniformity of the field. A new method is used to map the field uniformity in a fixed and variable frequency furnace. Frequency ranges larger than 1 GHz lead to uniform field distribution. Soil with an organic content of 82% was contaminated with PCB congeners #53 and #65 to ca. 400 ppm, and subjected to microwave exposure. Extracts of blanks and treated samples were analyzed with GC/MS. No breakdown products were observed in any of the extracts. The reduction of PCB in the extract was not dependent on the length of exposure to microwave energy. Soil temperature had the greatest effect on the reduction efficiency in the extract: the reduction efficiency at 170°C averaged at 55%, at 100°C it was only 17% for PCB #53. In preliminary experiments no PCBs were detected in the offgas. Additional experiments have to investigate the fate of the PCB in the soil as the offgas

Review of novel and emerging proximal soil moisture sensors for use in agriculture

The measurement of soil moisture in agriculture is currently dominated by a small number of sensors, the use of which is greatly limited by their small sampling volume, high cost, need for close soil–sensor contact, and poor performance in saline, vertic and stony soils. This review was undertaken to explore the plethora of novel and emerging soil moisture sensors, and evaluate their potential use in agriculture. The review found that improvements to existing techniques over the last two decades are limited, and largely restricted to frequency domain reflectometry approaches. However, a broad range of new, novel and emerging means of measuring soil moisture were identified including, actively heated fiber optics (AHFO), high capacity tensiometers, paired acoustic / radio / seismic transceiver approaches, microwave-based approaches, radio frequency identification (RFID), hydrogels and seismoelectric approaches. Excitement over this range of potential new technologies is however tempered by the observation that most of these technologies are at early stages of development, and that few of these techniques have been adequately evaluated in situ agricultural soils

Comparison of techniques for measuring the water content of soil and other porous media

The measurement of water in soil on a potential, gravimetric or volumetric basis is considered, with studies concentrating on the measurement of water by dielectric and neutron moderation methods. The ability of the time-domain reflectometry technique to measure water content simultaneously at different spatial locations is an important advantage of the technique. The reported apparent dielectric by the TRASE� time-domain reflectometer and Pyelab time-domain reflectometry systems is sensitive to change in extension cable length. In some soil, e.g. a commercial sand, the response to increasing extension length of extension cable is linear. For other soil a linear response occurs for certain lengths of cable at different moisture contents. A single model accounting for clay content, extension cable length, time-domain reflectometry system, probe type and inherent moisture conditions explained 62.2 % of variation from the control (0 m extension) cable. The extension cable causes a decrease in the returning electromagnetic-wave energy; leading to a decline in the slope used in automatic end-point determination. Calibration for each probe installation when the soil is saturated, and at small water contents is recommended. The ability of time-domain reflectometry, frequency-domain and neutron moderation techniques in measuring soil water content in a Brown Chromosol is examined. An in situ calibration, across a limited range of water contents, for the neutron moderation method is more sensitive to changing soil water content than the factory supplied 'universal' calibration. Comparison of the EnviroSCAN� frequency-domain system and the NMM count ratio indicates the frequency-domain technique is more sensitive to change in soil water conditions. The EnviroSCAN� system is well suited to continuous profile-based measurement of soil water content. Results with the time-domain reflectometry technique were disappointing, indicating the limited applicability of time-domain reflectometry in profile based soil water content measurement in heavy-textured soil, or soil with a large electrical conductivity. The method of auguring to a known depth and placement of the time-domain reflectometry probe into undisturbed soil is not recommended. A time-domain reflectometry system is adapted for in situ measurement of water in an iron ore stockpile. The laboratory calibration for water content of the processed iron ore compares favourably to a field calibration. In the field study, the 28 m extension cable used to connect the probes to the time-domain reflectometry affected the end-point determination of the time-domain reflectometry system. To account for this, 0.197 should be subtracted from the reported apparent dielectric before calculation of volumetric moisture content