A Computational Channel Model for Magnetic Induction-Based Subsurface Applications

There are many underground applications based on magnetic fields generated by an oscillating magnetic source. For them, a magnetic dipole in a three-layered region with upper semi-infinite air layer can be a convenient idealization used for their planning, development, and operation. Solutions are in the form of the well-known Sommerfeld integral expressions that can be evaluated by numerical methods. A set of field expressions to be numerically evaluated by an efficient algorithm are not collected comprehensively yet, or at least in a directly usable form. In this paper, the explicit magnetic field solutions for the vertical magnetic dipole and the horizontal magnetic dipole for a general source-observer location are derived from the Hertz vector. They can be properly combined to model the problem of a tilted magnetic dipole source for horizontally or inclined stratified media. As a result, a complete set of integral equations of the Sommerfeld type valid from the near zone to the far zone are formulated. A method for numerical evaluation of the field expressions for high accurate computations is described. The numerical results are validated using the finite element method for all the possible source-receiver configurations and three well-spanned frequencies of typical subsurface applications. Both numerical solutions agree according to the normalized root-mean-square error-based fit metric. Numerical results for two cases of study are presented to see its usefulness for subsurface applications. A MATLAB implementation of the mathematical description outlined in this paper and the proposed evaluation method is freely available for download

Through-the-earth electromagnetic trapped miner location systems : a review

"In its role of providing technical assistance to the mining industry, the Bureau of Mines' Tuscaloosa Research Center has conducted research to develop trapped miner location systems which would aid in locating miners trapped by underground mining disasters. Efforts to produce electromagnetic systems for the location of trapped miners underground and to communicate with them were surveyed, from the 1920's to 1981. Theoretical studies of through-the-earth electromagnetic transmissions are described as well as studies of the electrical characteristics of various rocks, minerals, and soil. Several trapped miner location systems are reviewed including the Westinghouse systems, the DEVELCO system, and an automated three-dimensional location system, and the phase difference of arrival technique. Tangential research, relevant to trapped miner location systems is described. A comprehensive bibliography covering all aspects of trapped miner, through-the-earth electromagnetic location and communications systems is appended." - NIOSHTIC-2NIOSHTIC no. 1000482

Evaluation of metal detection audio alert signals of AN/PSS-14 by means of real time visualization

The sweep arm of the AN/PSS-14 Landmine Detector attached to an independent visualization device will transform the AN/PSS-14 into a hand-held data acquisition system for conversion of real time MD and GPR audio alert signals into captured visual trace displays on an on-board PDA computer screen so that momentary sounds of millisecond durations can be captured and displayed for visual scrutiny and interpretation by analytical on-board data processing procedures. This is a part of a two-man team that is developing a visual data adapter for the AN/PSS-14 Landmine Detector where the current thesis is concentrating only on MD audio alerts. The visualization device displays the amplitude-time plot and the instantaneous frequency-time plots of the MD audio alert signal for better understanding and for distinction of metallic firing pins from metallic clutter. This is achieved by the identification of the metal type, which would be common in any given landmine field and by observing the symmetric deviations of the amplitude envelope along multiple sweep directions over a buried target. The analysis of this research is constrained to only vertical firing pins. Further, analyzing the frequencies of different types of firing pin (different metal types), it can be concluded that the frequency response of the AN/PSS-14 to metallic targets are specific to metals. This process is only applicable for single, isolated MD audio signals --Abstract, page iii

Searching for the Unmarked Henry Kinsey Family Graves at the VA Hospital Grounds in Dayton, Ohio, Using Magnetic, Electromagnetic, and Radar Methods

The Henry Kinsey family was among the first to settle in the Dayton, Ohio, region in the early 19th century. Henry, and his wife Eva, were buried near what is known as the deer keeper’s lodge, a small building where the deer keeper lived, on the modern-day Dayton Veterans Affairs hospital grounds. In the time since they have been buried, the location of their gravesites has been lost. The main purpose of this thesis is to locate and map their graves using multiple geophysical methods. A secondary purpose is to compare the effectiveness of each geophysical method. Three geophysical methods were used in this work: magnetics, electromagnetics, and ground penetrating radar. The magnetics survey was conducted using two Geometrics 857 proton precession magnetometers in a gradiometer configuration. The results of the magnetic survey show that there is a large magnetic anomaly running through the center of the survey area, likely an old utilities pipe. The data also show a significant anomaly coinciding with a surface artifact site, which is most likely the structure that stood next to the Kinsey family graves. The electromagnetics survey was conducted using a GSSI EMP-400 Profiler which utilized three frequencies simultaneously: 5kHz, 9kHz, and 15kHz. The electromagnetic data revealed a large anomaly through the center of the survey area, similar to the magnetics survey results. The data also showed a slight anomaly under the artifact site, although without the strength and clarity of the magnetics survey. The ground penetrating radar survey used a GSSI SIR-3000 system with a 400 MHz bistatic antenna. This survey yielded the best results, showing the extent of the artifact site in the subsurface. A small 3D survey was conducted over a unique anomaly that is a potential grave location. The GPR data would have shown even more, however, there are numerous trees within the survey area and their roots severely inferred with the GPR data. Based upon the data collected over the course of this report, no precise location for the Kinsey family graves can be stated, although the artifact site can be said to be the location of the deer keeper’s lodge. This allows for future, more focused surveys to be conducted over this site to definitively locate the Kinsey family graves

An algorithm for the automatic resolution of the position, orientation and dipole moment of a magnetic dipole antenna buried in rock

Abstract In this paper, an algorithm for accurately finding the position, orientation and dipole moment of a transmitting dipole antenna buried in rock is presented. The algorithm is based on simplified radiation equations that are shown to be valid within a region of space in the extreme near field surrounding the antenna called termed quasi-static region. Within this region, medium dependent propagation effects are negligible, allowing accurate, medium independent resolution of position, orientation and dipole moment. The magnetic field magnitude and direction values observed at a number of arbitrarily located points in space are used by the algorithm to generate a system of nonlinear equations. This system of equations is solved using a simultaneous multi-variable Newton-Raphson solver with line searches and backtracking providing a measure of global convergence. An additional method, based on an iterated random search, further improves the global convergence capability of the algorithm. If the dipole moment of the transmitting antenna is known, measurements from two observer points are sufficient to resolve the position and orientation of the dipole. If the dipole moment is unknown, three observer points are required to solve for the unknown position, orientation and dipole moment. The algorithm is able to find an exact solution using exact theoretical measurements, and a minimised least squares solution where measurements are subject to noise. The theory relating to the algorithm is discussed including distance-frequency relations for the quasistatic region of a number of common rock types. Probabilistic modelling, simulation and test results of the algorithm are also included

A review of the use of geophysics in base- and precious-metal exploration

The object of geophysical surveys in mineral exploration has traditionally been to detect subsurface geological features, which may reflect the presence of mineralization in depth and, if possible, to measure the dimensions of the causative body. Geophysical methods may also be used to locate extensions to known mineralization and for determining the size, depth and internal characteristics of an orebody. Marked improvements in geological concepts of ore genesis have led to a better appreciation, amongst geologists, of mineralized environments, and this has had an effect on the use of geophysics in recent years. Geophysical surveys are being increasingly used as an aid in environmental reconstructions and the results of regional surveys may be used to provide an indirect guide to ore. One of the main applications of geophysics lies in areas where the orebodies and associated structures are not exposed, as most geophysical measurements are more expensive than surface geological or geochemical surveys

AN OVERVIEW OF MAGNETIC METHOD IN MINERAL EXPLORATION

In modern times, the economic strength of a nation, the standard of living and independence of her citizens depend on the nation's industrial strength and her economic buoyancy. These two parameters, that is, the nation's industrial strength and the buoyancy of the industries in each country, sometimes form the bases for classifying the countries as "developed" (e.g., America and Japan) or "developing" (e.g., Nigeria and Ghana) with every nation striving to achieve the former status. The availability of the raw materials needed by most industries is one of the primary factors for the establishment of the industries. The raw material needs of most industries occur sporadically in one form or the other inside the earth's crust and the search for them as been one of man's major concerns. This paper gives the literature report about the use of magnetic method in mineral exploration. Magnetic exploration also referred to as “potential field” exploration is used to give geoscientist an indirect way to “see” beneath the Earth’s surface by sensing physical properties of rocks (magnetization). Magnetic method exploration can help locate minerals. Potential field survey is relatively inexpensive and can quickly cover large areas of ground. The method is relatively cheap, non-invasive and non-destructive environmentally speaking

Quantitative Integration of Multiple Near-Surface Geophysical Techniques for Improved Subsurface Imaging and Reducing Uncertainty in Discrete Anomaly Detection

Currently there is no systematic quantitative methodology in place for the integration of two or more coincident data sets collected using near-surface geophysical techniques. As the need for this type of methodology increases—particularly in the fields of archaeological prospecting, UXO detection, landmine detection, environmental site characterization/remediation monitoring, and forensics—a detailed and refined approach is necessary. The objective of this dissertation is to investigate quantitative techniques for integrating multi-tool near-surface geophysical data to improve subsurface imaging and reduce uncertainty in discrete anomaly detection. This objective is fulfilled by: (1) correlating multi-tool geophysical data with existing well-characterized “targets”; (2) developing methods for quantitatively merging different geophysical data sets; (3) implementing statistical tools within Statistical Analysis System (SAS) to evaluate the multiple integration methodologies; and (4) testing these new methods at several well-characterized sites with varied targets (i.e., case studies). Three geophysical techniques utilized in this research are: ground penetrating radar (GPR), electromagnetic (ground conductivity) methods (EM), and magnetic gradiometry. Computer simulations are developed to generate synthetic data with expected parameters such as heterogeneity of the subsurface, type of target, and spatial sampling. The synthetic data sets are integrated using the same methodologies employed on the case-study sites to (a) further develop the necessary quantitative assessment scheme, and (b) determine if these merged data sets do in fact yield improved results. A controlled setting within The University of Tennessee Geophysical Research Station permits the data (and associated anomalous bodies) to be spatially correlated with the locations of known targets. Error analysis is then conducted to guide any modifications to the data integration methodologies before transitioning to study sites of unknown subsurface features. Statistical analysis utilizing SAS is conducted to quantitatively evaluate the effectiveness of the data integration methodologies and determine if there are significant improvements in subsurface imaging, thus resulting in a reduction in the uncertainty of discrete anomaly detection