Performance of Electrical Spectroscopy using a Resper Probe to Measure the Salinity and Water Content of Concrete or Terrestrial Soil

This paper discusses the performance of electrical spectroscopy using a RESPER probe to measure the salinity s and volumetric content {\theta}W of the water in concrete or terrestrial soil. The RESPER probe is an induction device for spectroscopy which performs simultaneous and non invasive measurements of the electrical RESistivity 1/{\sigma} and relative dielectric PERmittivity {\epsilon}r of a subjacent medium. Numerical simulations establish that the RESPER can measure {\sigma} and {\epsilon} with inaccuracies below a predefined limit (10%) up to the high frequency band (HF). Conductivity is related to salinity and dielectric permittivity to volumetric water content using suitably refined theoretical models which are consistent with the predictions of Archie's and Topp's empirical laws. The better the agreement, the lower the hygroscopic water content and the higher s; so closer agreement is found with concrete containing almost no bonded water molecules provided these are characterized by a high {\sigma}. A novelty of the present paper is the application of a mathematical- physical model to the propagation of errors in the measurements, based on a sensitivity functions tool. The inaccuracy of salinity (water content) is the ratio (product) between the conductivity (permittivity) inaccuracy, specified by the probe, and the sensitivity function of salinity (water content) relative to conductivity (permittivity), derived from the constitutive equations of the medium. The main result is the model's prediction that the lower the inaccuracy for the measurements of s and {\theta}W (decreasing by as much as an order of magnitude from 10% to 1%), the higher {\sigma}; so the inaccuracy for soil is lower.Comment: 45 pages, 5 figures, 1 tabl

Electromagnetic Pulse Sounding for Surveying Underground Water

This project supported in part by the Office of Water Resources Research U. S. Department of the Interior Washington, D. C. under Project B-028-OHIOA number of approaches have been explored for measuring the water content of soil electrically. In contrast with traditional measurements, which utilize electric currents at DC or at specific frequencies, our techniques have been based on the transmission and reflection of sharp, regularly repeated pulses. Such pulse measurements can be shown to be equivalent to measuring the electrical properties at all frequencies in a very wide band, and therefore the possibility of extracting the desired information is much greater than with single-frequency measurements. Because the information content of the signal is great, data processing can be used to extract those features which relate most directly to moisture content and reject those which appear to depend more on soil inhomogenieties. For example, it was found that the attenuation in the frequency band of approximately 10 to 20 MHz had a much higher correlation with soil moisture than that in other frequency bands for the actual field conditions under which our measurements were made. This information content increase is obtained by means of sophisticated research equipment. The measurements reported herein were made and processed under real-time computer control. They include the signal scattered from known buried targets, transmission measurements through the ground, and the measurement of reflections in a coaxial test cell, all with pulses containing very wide frequency bands. The results are encouraging in that definite correlations with moisture were found. Unfortunately the one-year time limitation of this effort, much of it spent in instrumentation development, was insufficient to allow testing these correlations quantitatively over extended time periods or in a variety of locations. Thus the techniques must be evaluated at present as promising, but not fully proven. It should be noted that, while the research system to obtain this information is complex, field equipment based on these techniques need not be unduly complicated or expensive. Once the features relating to moisture content under the greatest variety of field conditions are identified, means for extracting this information more simply should be devised. This is proposed as the objective for continuation of this effort.Summary -- Introduction -- 1. The Measuring System -- 2. Data Processing -- 3. Underground Moisture Content Monitoring by Measurement of Buried Target Signatures -- 4. Sampled Moisture Conditions -- 5. Underground Propagation Experiment -- 6. Reflection Measurements on Soil Samples in a Vertical Coaxial Test Cell -- 7. Propagation Calculations -- Conclusions -- Recommendations -- References -- Appendix I - Transmission Measurements using a Buried Antenn

Modeling Ground Penetrating Radar (GPR) Technology for Seed Planting Depth Detection using Numerical Scheme based on Finite Difference Time Domain (FDTD) Method

Ground Penetrating Radar (GPR) is an electromagnetic (EM) signal based technology, commonly used as a non-destructive technique to explore subsurface features and identify different depth profiles in materials. The overall goals of this work is to evaluate GPR for non-destructive mapping of seed planting depth. Soils are inherently complex materials and numerous factors affect GPR behavior. The fundamental factors affecting GPR response are dielectric permittivity, magnetic permeability, and electrical conductivity, which are influenced by soil bulk density, texture, salinity, organic matter, volumetric water content, seed properties and physical geometry. To successfully optimize GPR’s ability to detect seed planting depth, the influence of these factors must be evaluated. This paper describes the development of a single dimensional GPR simulation model, based on finite difference time domain (FDTD) method, to evaluate the use of GPR sensing of seed planting depth. The simulation results shows that the EM signal is highly sensitive to high values of the electrical conductivity. High permittivity values decrease the EM signal velocity, wavelength and strength. A combination of these two properties leads to a significant EM signal attenuation ranging from 0 to ~ 800 dBm-1 as the signal traverses through the soil and seed. The lack of sufficient dielectric contrast between soil and seed presents a challenge on the detectability of the reflected signal by the radar receiver, therefore a sufficient dielectric contrast between the soil and seed has to be present to allow the GPR to be a viable tool to map the seed planting depth

Using gprMax to Model Ground-Penetrating Radar (GPR) to Locate Corn Seed as an Attempt to Measure Planting Depth

Planting depth (PD) plays an essential role in crop production by substantially impacting germination rates and yield potential. However, techniques to measure PD nondestructively have not been developed. A two-dimensional gprMax simulation study was conducted to investigate the effects of soil electromagnetic properties on ground-penetrating radar (GPR) waves. The primary objective was to examine the possibility of using GPR as a nondestructive sensor to detect subsurface corn seeds with the goal of measuring PD. A conventional fixed-offset gprMax antenna in contact with the soil surface was used in the simulations. Corn seed models of different materials and sizes were simulated, with properties of natural and synthetic (metal) corn seeds. The seed models were spherical, with radial dimensions of 0.006 and 0.024 m to simulate small and large corn seeds, respectively. Corn seed models were embedded in three homogeneous soil models (sandy loam, loam, and clay), and 1.6 and 2.6 GHz antenna models were used as excitation frequencies. A-scans and B-scans were obtained from the simulations. The A-scans showed that all targets (small natural corn and metal corn models, and large natural corm and metal corn models) successfully provided response amplitudes proportional to their dielectric properties in sandy loam and loam, but not in clay. In high bulk density soils, GPR waves failed to penetrate the soil models, and the targets were not detected. The 2.6 GHz antenna provided better response amplitudes from the targets. In the driest soil models (2.5%, and 5%), no response amplitude signatures were observed. In dry and relatively dry soil models (15%), the simulation times were much shorter to obtain a response amplitude from the targets (with feeble response amplitudes) compared to relatively wetter soils. To validate these models, laboratory experiments were conducted with three treatment factors (soil type, planting depth, and moisture content). In dry soils, corn seeds could be detected using a 2.6 GHz GPR antenna; however, the detection varied substantially within replicates of the same moisture group. Further research is necessary to understand the effects of soil moisture on the detection variability of buried corn seeds

Soil Moisture and Permittivity Estimation

The soil moisture and permittivity estimation is vital for the success of the variable rate approaches in the field of the decision agriculture. In this chapter, the development of a novel permittivity estimation and soil moisture sensing approach is presented. The empirical setup and experimental methodology for the power delay measurements used in model are introduced. Moreover, the performance analysis is explained that includes the model validation and error analysis. The transfer functions are reported as well for soil moisture and permittivity estimation. Furthermore, the potential applications of the developed approach in different disciplines are also examined

Dynamic Response of Silo Supporting Structure under Pulsating Loads

Silo quaking is a time varying mass structural dynamic problem and the existence of a silo quake spectrum is confirmed in this research. The outcomes confirm that silo quaking can be prevented by providing the silo structure with sufficient mass, stiffness and damping to counterbalance the effects of pulsating forces and mass losses. Furthermore, dynamic structural analysis algorithms and software need to be developed to solve time varying mass structural dynamic problems

Electromagnetic Waves in Contaminated Soils

Soil is a complex, potentially heterogeneous, lossy, and dispersive medium. Modeling the propagation and scattering of electromagnetic (EM) waves in soil is, hence, more challenging than in air or in other less complex media. This chapter will explain fundamentals of the numerical modeling of EM wave propagation and scattering in soil through solving Maxwell’s equations using a finite difference time domain (FDTD) method. The chapter will explain how: (i) the lossy and dispersive soil medium (in both dry and fully water-saturated conditions), (ii) a fourth phase (anomaly), (iii) two different types of transmitting antennae (a monopole and a dipole), and (iv) required absorbing boundary conditions can numerically be modeled. This is described through two examples that simulate the detection of DNAPL (dense nonaqueous-phase liquid) contamination in soil using Cross-well radar (CWR). CWR —otherwise known as cross-borehole GPR (ground penetrating radar)—modality was selected to eliminate the need for simulation of the roughness of the soil-air interface. The two examples demonstrate the scattering effect of a dielectric anomaly (representing a DNAPL pool) on the EM wave propagation through soil. The objective behind selecting these two examples is twofold: (i) explanation of the details and challenges of numerical modeling of EM wave propagation and scattering through soil for an actual problem (in this case, DNAPL detection), and (ii) demonstration of the feasibility of using EM waves for this actual detection problem

An interdisciplinary approach towards improved understanding of soil deformation during compaction

International audienceSoil compaction not only reduces available pore volume in which fluids are stored, but it alters the arrangement of soil constituents and pore geometry, thereby adversely impacting fluid transport and a range of soil ecological functions. Quantitative understanding of stress transmission and deformation processes in arable soils remains limited. Yet such knowledge is essential for better predictions of effects of soil management practices such as agricultural field traffic on soil functioning. Concepts and theory used in agricultural soil mechanics (soil compaction and soil tillage) are often adopted from conventional soil mechanics (e.g. foundation engineering). However, in contrast with standard geotechnical applications, undesired stresses applied by agricultural tyres/tracks are highly dynamic and last for very short times. Moreover, arable soils are typically unsaturated and contain important secondary structures (e.g. aggregates), factors important for affecting their soil mechanical behaviour. Mechanical processes in porous media are not only of concern in soil mechanics, but also in other fields including geophysics and granular material science. Despite similarity of basic mechanical processes, theoretical frameworks often differ and reflect disciplinary focus. We review concepts from different but complementary fields concerned with porous media mechanics and highlight opportunities for synergistic advances in understanding deformation and compaction of arable soils. We highlight the important role of technological advances in non-destructive measurement methods at pore (X-ray tomography) and soil profile (seismic) scales that not only offer new insights into soil architecture and enable visualization of soil deformation, but are becoming instrumental in the development and validation of new soil compaction models. The integration of concepts underlying dynamic processes that modify soil pore spaces and bulk properties will improve the understanding of how soil management affect vital soil mechanical, hydraulic and ecological functions supporting plant growth