Enhancements to and Characterization of the Very Early Time Electromagnetic (VETEM) Prototype Instrument and Applications to Shallow Subsurface Imaging at Sites in the DOE Complex - Final Report

Field tests and deployments of VETEM is a flexible and highly effective new system for electromagnetic imaging that offers significant new 3D electromagnetic imaging capabilities in the shallow subsurface. Important new numerical modeling techniques have been produced, which are applicable to electromagnetic subsurface imaging, and suggest further research and development. In addition, this research has also produced a flexible, fast, and fully functional prototype VETEM system that has produced some remarkable subsurface images, has bridged the gap between pure research and applications, and is now available for use at DOE sites that have shallow subsurface imaging needs

Structural Trends of Ijeda-Iloko Area as Interpreted From Total Component of Ground Magnetic Data

Ground magnetic survey of Ijeda and Iloko towns in Oriade Local Government Area of Osun state Southwest Nigeria was performed. The study was carried out using high resolution proton precision geometric magnetometer which involves the use of Total Component of the ground magnetic anomaly data running through traverses 7, 8, 9 and 13. This research focuses on delineation of faults in this part of the highly mineralized Ilesa schist belt. The field data was qualitatively and quantitatively interpreted and the results gave values for the Total component measurements of ground magnetic anomaly which varied between a minimum negative peak value of about -330 gammas and a maximum positive peak value of about 80 gammas. Depth to the basement rock was estimated using half slope method. Information on wide range of magnetic intensities over the different rock types in this area were obtained from the quantitative interpretation using linear trends. The results generated were used to delineate rock boundaries, bedrock topography major and minor faults

Survey Plan For Characterization of the Subsurface Underlying the National Aeronautics and Space Administration's Marshall Space Flight Center in Huntsville, Alabama

Topic considered include: survey objectives; technologies for non-Invasive imaging of subsurface; cost; data requirements and sources; climatic condition; hydrology and geology; chemicals; magnetometry; electrical(resistivity, potential); optical-style imaging; reflection/refraction seismics; gravitometry; photo-acoustic activation;well drilling and borehole analysis; comparative assessment matrix; ground sensors; choice of the neutron sources; logistic of operations; system requirements; health and safety plans

A Comprehensive Forward Model for Imaging under Irregular Terrain Using RF Tomography

Imaging of tunnel networks under irregular terrain using RF tomography is generalized to include the possibility of magnetic dipoles (i.e., electric loops) either as transmitting or receiving devices. Forward scattering models are presented, and a generalized method for computing numerical dyadic Green’s functions is detailed. Explicit formulas for fast numerical implementation are also presented. The paper is corroborated with numerical simulations aimed at validating formulas

Accurate Tree Roots Positioning and Sizing over Undulated Ground Surfaces by Common Offset GPR Measurements

Tree roots detection is a popular application of the Ground-penetrating radar (GPR). Normally, the ground surface above the tree roots is assumed to be flat, and standard processing methods based on hyperbolic fitting are applied to the hyperbolae reflection patterns of tree roots for detection purposes. When the surface of the land is undulating (not flat), these typical hyperbolic fitting methods becomes inaccurate. This is because, the reflection patterns change with the uneven ground surfaces. When the soil surface is not flat, it is inaccurate to use the peak point of an asymmetric reflection pattern to identify the depth and horizontal position of the underground target. The reflection patterns of the complex shapes due to extreme surface variations results in analysis difficulties. Furthermore, when multiple objects are buried under an undulating ground, it is hard to judge their relative positions based on a B-scan that assumes a flat ground. In this paper, a roots fitting method based on electromagnetic waves (EM) travel time analysis is proposed to take into consideration the realistic undulating ground surface. A wheel-based (WB) GPR and an antenna-height-fixed (AHF) GPR System are presented, and their corresponding fitting models are proposed. The effectiveness of the proposed method is demonstrated and validated through numerical examples and field experiments.Comment: 11 pages, 6 figures, accepted by IEEE TI

Low-frequency dipolar excitation of a perfect ellipsoidal conductor

International audienceThis paper deals with the scattering by a perfectly conductive ellipsoid under magnetic dipolar excitation at low frequency. The source and the ellipsoid are embedded in an infinite homogeneous conducting ground. The main idea is to obtain an analytical solution of this scattering problem in order to have a fast numerical estimation of the scattered field that can be useful for real data inversion. Maxwell equations and boundary conditions, describing the problem, are firstly expanded using low-frequency expansion of the fields up to order three. It will be shown that fields have to be found incrementally. The static one (term of order zero) satisfies the Laplace equation. The next non-zero term (term of order two) is more complicated and satisfies the Poisson equation. The order-three term is independent of the previous ones and is described by the Laplace equation. They constitute three different scattering problems that are solved using the separated variables method in the ellipsoidal coordinate system. Solutions are written as expansions on the few analytically known scalar ellipsoidal harmonics. Details are given to explain how those solutions are achieved with an example of numerical results

Revisiting the Low-Frequency Dipolar Perturbation by an Impenetrable Ellipsoid in a Conductive Surrounding

This contribution deals with the scattering by a metallic ellipsoidal target, embedded in a homogeneous conductive medium, which is stimulated when a 3D time-harmonic magnetic dipole is operating at the low-frequency realm. The incident, the scattered, and the total three-dimensional electromagnetic fields, which satisfy Maxwell’s equations, yield low-frequency expansions in terms of positive integral powers of the complex-valued wave number of the exterior medium. We preserve the static Rayleigh approximation and the first three dynamic terms, while the additional terms of minor contribution are neglected. The Maxwell-type problem is transformed into intertwined potential-type boundary value problems with impenetrable boundary conditions, whereas the environment of a genuine ellipsoidal coordinate system provides the necessary setting for tackling such problems in anisotropic space. The fields are represented via nonaxisymmetric infinite series expansions in terms of harmonic eigenfunctions, affiliated with the ellipsoidal system, obtaining analytical closed-form solutions in a compact fashion. Until nowadays, such problems were attacked by using the very few ellipsoidal harmonics exhibiting an analytical form. In the present article, we address this issue by incorporating the full series expansion of the potentials and utilizing the entire subspace of ellipsoidal harmonic eigenfunctions

A Study on the Reconstruction of Moderate Contrast Targets Using the Distorted Born Iterative Method

Abstract-Previous tomographic methods using ultrasound for reconstructing sound speed and attenuation images suffered from convergence issues for targets with moderate speed of sound contrast. Convergence problems can be overcome by the use of the multiple frequency, distorted Born iterative method (DBIM). The implementation of DBIM for measurement configurations in which receiver positions are fixed was studied, and a novel regularization scheme was developed. The regularization parameter needed to stabilize the inversion process initially was found through the Rayleigh quotient iteration, then relaxed according to the relative residual error between the measured and estimated scattered fields. The DBIM was successfully stabilized for both full and partial receiver angular coverage without a significant loss in spatial resolution. The effects of variable density in the reconstructions were briefly explored through simulations. The ability to reconstruct targets with moderate contrast was validated through experimental measurements. Speed of sound profiles for balloons filled with saline in a background of water were reconstructed using multiple frequency DBIM techniques. The mean squared error for speed of sound reconstructions of the balloon phantoms with 16.4% sound speed contrast was 1.1%