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A computational tool was developed to visualize radar reflection coefficients for a lossy, two-layered half-space soil geometry as a function of incidence angle. Allowable input parameters include radar frequency, top soil layer thickness, and the complex dielectric properties of both soil layers. The tool is a Microsoft Excel program that can operate on any Windows-based personal computer.

In support of mine detection sensor development programs at the U.S. Army Night Vision and Electronic Sensors Directorate, both onsite and laboratory measurements of soil properties were conducted on soils from the Fort Belvoir, VA, indoor mine lane facility. The lanes contain six distinctly different soils. In an effort to characterize these soils for both current and anticipated sensor technologies, measurement activities included onsite seismic refraction data collection and laboratory measurements of physical property data, complex dielectric constants, magnetic susceptibilities, visual specular reflectances, broadband infrared reflectances, and soil mineralogy and chemistry.

An optical imaging system is described that simultaneously measures the wavelength dependence and polarization state dependence of light reflected from any surface. Potential applications of this technology include identifying man made objects from natural backgrounds, land cover classification, and a myriad of agricultural problems such as ground moisture measurements, estimation of crop health, etc. Polarization effects are quantified through the use of Stokes parameters. Both spatial and wavelength dependent data are collected simultaneously through the use of a phase only computer generated hologram as a diffraction grating. Image reconstruction is achieved through an inversion procedure called computed tomography., See Also ADA399665 .

An optical imaging system is described that simultaneously measures the wavelength dependence and polarization state dependence of light reflected from any surface. Potential applications of this technology include identifying man made objects from natural backgrounds, land cover classification, and a myriad of agricultural problems such as ground moisture measurements, estimation of crop health, etc. Polarization effects are quantified through the use of Stokes parameters. Both spatial and wavelength dependent data are collected simultaneously through the use of a phase only computer generated hologram as a diffraction grating. Image reconstruction is achieved through an inversion procedure called computed tomography., See Also ADA399664 .

The self-evaluations of four participants in the Jefferson Proving Ground, IN, UXO (unexploded ordnance) Technology Demonstrations, Phase III (1996), were reviewed to better understand the factors that control detection and/or discrimination of buried UXO by surface instruments. Among the conclusions drawn was the fact that each participant relied more heavily on human experience than model-driven data analysis to distinguish UXO from other objects. Furthermore, the simple magnetic dipole models that were used by some participants were shown to be inadequate for accurately predicting depth of burial and UXO orientation in most cases. Data analysis techniques and model predictions are not yet sophisticated enough to allow UXO discrimination using total field magnetometry.

Geological, geophysical, environmental, and geotechnical investigations were performed to characterize three unexploded ordnance (UXO) test sites at Jefferson Proving Ground (JPG), Indiana. The purpose of the characterization is to support: (I) Phase IV demonstrator planning and results assessment; (2) Additional assessments of Phase I-III; (3) Future use of JPG sites; and (4) Comparisons of the JPG sites with other UXO and landmine test and cleanup sites. Some observations made as a result of the investigations are outlined below. Soil samples collected from the three sites are classified, according to the Unified Classification System (USCS), chiefly as CH or CL and are generally characterized as clays, sandy clays, or silty clays. In the USCS, soil particles passing the No.200 sieve are considered silt or clay. X-ray diffraction analysis indicate that these soils contain little or no clay minerals and consist chiefly of very fine-grained (silt or clay-sized) silica particles. Relative dielectric permitivitties values generally range between l0-25 and were determined in the field and in the laboratory. Test results also indicate that the soils highly attenuate the propagation of electromagnetic waves. The depth of investigation for ground penetrating radar at the sites is limited to approximately 3.5 m.

This report contains dielectric property measurement results for five different materials that have been used as fillers for various inert landmines. The original data were collected in the form of the real and imaginary parts of the complex dielectric constant versus frequency utilizing a Hewlett-Packard 8510C Vector Network Analyzer System with an S-Parameter Test Set and a coaxial sample holder. Software developed at the U.S. Army Engineer Waterways Experiment Station was used to convert S-parameter measurements at selected frequencies into a complex dielectric constant. The materials were assumed to be nonmagnetic. Other useful electromagnetic properties were calculated from the dielectric constant and frequency, including an equivalent electrical conductivity, the loss tangent, power attenuation, and a normalized phase velocity. The section entitled "Fundamental Relationships," contains the formulae use to calculate these properties.

This report contains dielectric property measurement results for soils. The original data were collected in the form of the real and imaginary parts of the complex dielectric constant versus frequency utilizing a Hewlett-Packard 851 OC Vector Network Analyzer System with an S-Parameter Test Set and a coaxial sample holder. Software developed at the U.S. Army Engineer Waterways Experiment Station was used to convert S-parameter measurements at selected frequencies into a complex dielectric constant. The soils were assumed to be nonmagnetic. Other useful electromagnetic properties were calculated from the dielectric constant and frequency, including an equivalent electrical conductivity, the loss tangent, power attenuation, and a normalized phase velocity. The section entitled, "Fundamental Relationships," contains the formulae used to calculate these properties. Additional physical parameters of the soil samples that are included in the report include their dry density, volumetric moisture content, and temperature. Measurement results and calculated parameters are listed at four selected frequencies and displayed as a function of volumetric moisture content. The intent of presenting data in this way is to demonstrate the experimental observation that the real part of the dielectric constant, as well as the normalized phase velocity are strong functions of volumetric moisture and reasonably independent of soil texture. Other parameters are clearly dependent on soil texture, and, given enough data from several different types of soils, their graphs versus moisture content would show a great deal of scatter. The four frequencies chosen for data presentation span the range of frequencies normally associated with ground penetrating radars.

This report contains dielectric property measurement results for soils. The original data were collected in the form of the real and imaginary parts of the complex dielectric constant versus frequency. The data collection apparatus was a Hewlet-Packard 85l0C Vector Network Analyzer System with an S-Parameter Test Set. Software developed at the U.S. Army Engineer Waterways Experiment Station was used to convert S-parameter measurements at selected frequencies into a complex dielectric constant. The soils were assumed to be nonmagnetic. Other useful electromagnetic properties were calculated from the dielectric constant and frequency, including an equivalent electrical conductivity, the loss tangent, power attenuation, and a normalized phase velocity. The section entitled, "Fundamental Relationships," contains the formulae used to calculate these properties. Additional physical parameters of the soil samples that are included in the report include their dry density, volumetric moisture content, and temperature.

A number of simple experiments were performed on a microwave reflectometer, operating at 60 MHz, to test the feasibility of its use as a tool for accurately measuring the complex electrical properties of soils. Such knowledge could be used to predict electromagnetic wave attenuation, the volumetric moisture contained within soil near the probe surface, and, through the relative changes in soil properties either over surface areas or as a function of depth below the surface, the presence of harmful contaminants. Background information contained within this report includes a review of similar microwave sensor applications and a description of the basic relationships used to convert sensor voltage measurements into relative dielectric permittivity and conductivity. Experiments were conducted to investigate the volume of soil that would be measured by the soil and to determine the sensitivity of the instrument. While permittivity measurements appeared to be quite good, conductivity measurements in low conductivity materials were not as reliable. A simple analytical study indicated that the conductivity measurements would be quite sensitive to the accuracy of the voltmeter being used by the reflectometer. In most soils, the frequency of operation and the sensitivity of this system will allow the field lines to extend about 1 cm away from the probe surface, making the probe ideal for surface measurements and well suited to being placed in a borehole or cone penetrometer environment to obtain vertical profiles of soil properties. Numerous improvements to the measurement system were recommended to improve its sensitivity and utility.

An industry-standard vector network analyzer system was used to measure the complex reflection and transmission coefficients of 12 different fine-grained soils over a frequency range of 45 MHz to 26.5 GHz. Measurement variables included sample temperature (10, 20, 30, and 40 C), the amount of distilled, deionized water added to each soil sample, and the dry density of the soil in each sample holder (an uncontrolled parameter because of the sample preparation procedure). Data are presented both as a function of frequency at fixed temperatures and moisture content and as a function of moisture content at fixed temperatures and frequencies. Complex results are expressed in numerous ways, including the real and imaginary parts of the complex relative dielectric constant, loss tangent, electrical conductivity (through its relationship to the imaginary part of the dielectric constant), phase velocity normalized to the speed of light in a vacuum, and power attenuation in decibels/meter. Data support earlier models of a critical moisture content. Furthermore, for all but the very lowest frequencies, the data demonstrate that the permittivity of the soils, when considered as a function of volumetric moisture content, can be viewed as independent of soil type. Low-frequency losses in the soil/water/air mixtures are attributed to Maxwell-Wagner effects and ionic conductivity. Soils containing expandable clays demonstrate losses due to bound water of hydration. High-frequency losses are the result of free water molecular dipole relaxation. While both bilinear and least-square polynomial fits to permittivity data for all soil types at selected frequencies are quite acceptable, exponential models do not fit the data well. (MM)

A laboratory measurement program was conducted to explore the fundamental electrical properties of organic contaminants and contaminant/soil mixtures. Complex reflection and transmission coefficients measured by a vector network analyzer system for samples contained in coaxial sample holders were used to generate electrical properties of the pure substances and the mixtures. The frequencies covered by these experiments ranged from 43 MHz to 26.5 GHz, and sample temperatures were held fixed at 10, 20, 30, and 40 deg C. Data were reported in the forms of the complex dielectric constant, conductivity, loss tangent, normalized phase velocity, and power attenuation. Simple volume-weighted mixing models for predicting the real part of the complex dielectric constant (permittivity) were applied successfully to single-frequency data. The rationale behind the development and some of the limitations of mixing models are discussed. The results of this study indicate that permittivity measurements, alone, will not be useful in detecting small concentrations of contaminants in soils. On the other hand, spectroscopic data that cover a frequency range large enough to reveal the dielectric relaxation loss phenomenon that occurs in many organic contaminants may prove to be useful as a detection and/or identification tool. jg

A reflection/transmission laboratory apparatus and data collection methodology are described that can be used to measure the complex dielectric response of moist soils over the 100 MHz-18 GHz frequency range. The experimental setup includes a square cross-sectional coaxial sample holder, a vector network analyzer system for signal generation and detection, and an external bath for sample temperature control. Data collected on liquids whose dielectric response is well known verify that the electrical property calculation algorithm functions properly. Complex dielectric constant, Permittivity, Conductivity, Soil, Microwave., See also Report 1, ADA275980.

As a precursor to developing a well-documented database of complex electrical properties of soils as a function of signal frequency, sample moisture, sample temperature, and soil type, a comprehensive study of existing data collection methodology and analytical modeling was undertaken. Of particular utility are chronological tables of experimental and analytical milestones as well as an extensive reference list. Several appendices are included that are helpful in understanding soil-electromagnetic wave interactions and new concepts in modeling soil structure. Complex dielectric constant, Microwave, Soil, Conductivity, Permittivity., See also Report 2, ADA275982.

This report contains the results of a number of test site characterization measurements conducted at the US Marine Base in Twentynine Palms, California during the second week of October 1990. Work conducted during this field experiment included the collection of soil samples at various depths within the first meter of the ground surface that were later used for classification and petrography studies, the measurement of surface roughness at several locations, and the manual recording of ground surface anomalies within the test area. These measurements were made to provide ground truth information in support of an airborne synthetic aperture radar experiment being conducted at the Marine base during the same time period.

Recent experimental data on soils showing that the application of loads with submillisecond rise times results in significant rate-dependent compressibility behavior have prompted the need for a one-dimensional plane wave propagation code for layered rate-dependent hysteretic or visco-compacting materials. An explicit one-dimensional finite element code--named ONED3P--was developed which incorporates a three-parameter (spring and dashpot) mechanical model consisting of a linear spring and dashpot in series coupled in parallel with a piecewise linear hysteretic or compacting spring. ONED3P allows for analysis of a column of multilayered visco-compacting soils loaded by a digitized surface pressure-time history. Any set of consistent units may be used with this code and results may be obtained in the form of stress-, strain-, acceleration-, velocity-, and/or displacement-time histories as well as stress-strain curves using standard Calcomp software. Several demonstration problems were calculated using ONED3P to evaluate its features and capabilities against (a) available analytical solutions for viscous and nonviscous problems, (b) other code solutions, and (c) measurements from field experiments that evince rate-dependent soil behavior. In general, results were extremely good. Special attention was given to the effects of loading rate or frequency on wave speeds in viscous media and to methods of deriving the ONED3P model parameters from laboratory material property test data. Program listings and a user's guide are included.

The results of analytical studies are presented in which (1) the SAP IV elastic finite-element (FE) code was used to perform modal analyses for a rectangular structure in vacuo and embedded in different backfill materials; and (2) a series of dynamic and static two-dimensional (2D), plane-strain, FE, structure-medium interaction (SMI) code calculations were performed using the HONDO code. The HONDO code SMI calculations were made to investigate the effect of variations in (1) surface airblast loadings; and (2) constitutive properties of the backfill region around a hypothetical, shallow-buried structure on the transient loading environments experienced by the structure. The model analyses showed that the natural frequencies increased as the quality of the material surrounding the structure increases. They also indicated that the planned SMI calculations would have sufficient frequency response. There was a noticeable reduction in the frequencies at which the structures responded in the HONDO code calculations due to a decrease in stiffness of the soil backfill. A linear elastic single-degree-of-freedom system model based on the predominant natural mode of the embedded structure simulated the response of the structure to the three different airblast loadings only when a 20 to 40 percent of critical damping was applied. The damping is believed to be necessary to account for energy removed from the elastic structure because of radiation into the surrounding media and the hysteretic nature of this media.