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Spie Press Book

Discrimination of Subsurface Unexploded Ordnance
Author(s): Kevin A. O'Neill
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Book Description

Unexploded ordnance (UXO) pose a persistent and expensive problem throughout the world; over 11 million acres are potentially contaminated in the U.S. alone. However, detection requires a very high degree of reliability, the false alarm rate is typically enormous, and cleanup costs are very high.

This Tutorial Text addresses the unique challenges of UXO detection and the following topics:

  • fundamental physics and phenomenology;
  • new, successful modeling and analysis methods;
  • the design, development, and testing of new instruments that provide expanded and superior data;
  • innovative processing techniques; and
  • highly successful discrimination performance in blind field tests at standardized sites.
  • The book is written for lay scientists and engineers, as well as specialists in the field, requiring only some familiarity with basic vector calculus and matrix methods, common statistical concepts, and elementary physics.

    Book Details

    Date Published: 5 January 2016
    Pages: 234
    ISBN: 9781628418668
    Volume: TT102

    Table of Contents
    SHOW Table of Contents | HIDE Table of Contents

    1 The Problem and Its Nature
    1.1 Discrimination, Inverse Problems, and What Follows
    1.2 Governing Equations and Concepts
         1.2.1 Potentials and the scalar Green function
    1.3 Wires, Loops, and Dipoles
         1.3.1 Tensor Green functions for strong conductors

    2 Basic Phenomenology
    2.1 Primary and Secondary Fields, Induced Response
         2.1.1 Inductive response and coils
         2.1.2 Triaxial infinitesimal dipole response model (TIDRM)
    2.2 Skin Depth, and Diffusion Time and Depth
         2.2.1 Frequency domain
         2.2.2 Time domain
    2.3 Canonical Cases and Associated Response Patterns
         2.3.1 Wire loops and relaxation
         2.3.2 The sphere
         2.3.3 Cylinders, spheroids, and ellipsoids
    2.4 The Environment
         2.4.1 Response from the natural environment
         2.4.2 Metallic clutter

    3 MQS Modeling and Fundamental Sensitivities
    3.1 Exploration of the Omnipresent TIDRM
         3.1.1 Special properties of the polarizability tensor
    3.2 Orientation, Aspect Ratio, and Cautions on the TIDRM
    3.3 Representation and Parameterization of Responses
         3.3.1 Examples and ulterior motives
    3.4 Interaction between Bodies
         3.4.1 Approaches and methods
         3.4.2 Interaction phenomenology

    4 Inverse Problems and Solving for Quantities of Interest
    4.1 Ill-Conditioning, Noise, and Null Spaces
    4.2 Pseudo-inverses and Least-Squares Solutions
    4.3 Least Squares and Optimization
         4.3.1 Regularization, weighting, and Bayesian forms
         4.3.2 Gradient methods, differential evolution, and structuring the search
    4.4 An Illustration

    5 Sensors and the Modeling They Require
    5.1 FD Devices
    5.2 TD Devices
    5.3 Positioning and Beacons
    5.4 Established and Emerging Instruments

    6 Advanced Physical Modeling of Responses
    6.1 The Method of Auxiliary Sources
    6.2 The Small Penetration Approximation
    6.3 Fast Forward Models via the Standardized Excitations Approach
    6.4 The Normalized Surface Magnetic Source Method
         6.4.1 Formulation
         6.4.2 Total NSMS as a discriminator

    7 Computation Directly Supporting Discrimination
    7.1 Real-Time Surveying Techniques
         7.1.1 Joint diagonalization
         7.1.2 Object location by HAP
    7.2 Multiple and Heterogeneous Objects, and the ONVMS Method
         7.2.1 Formulation
         7.2.2 Total ONVMS polarizabilities as discriminators
    7.3 Clustering as Unsupervised Learning
         7.3.1 K-means agglomerative clustering
         7.3.2 Hierarchical agglomerative clustering

    8 Classification
    8.1 Some General Perspectives on Discrimination Processing
    8.2 Kernel Methods and Partitioning via Supervised Training
    8.3 Semi-supervised and Active Learning Systems
    8.4 Likelihood and Bayesian Forms
    8.5 ROC Curves
    8.6 Field Testing and Complete Processing Sequences
    8.7 Looking Back and Ahead

    Appendix: Vector, Tensor, and Matrix Notation


    Buried unexploded ordnance (UXO) poses a persistent, challenging, and expensive cleanup problem. Whether on military practice lands or at the sites of past conflicts, many dropped bombs and fired projectiles failed to explode when they penetrated the ground, thus affecting the accessibility of millions of acres at thousands of sites in the US alone. Globally, the problem is even more extensive and dauntingly diverse. The cleanup of UXO sites is particularly challenging because detection must be extraordinarily reliable and remediation extremely careful. Beyond the challenges of problematic terrain, the sheer diversity of possible ordnance types compounds the difficulties inherent in the fuzziness of what practicable sensors provide. In most locations where some ordnance did not explode, many more items have indeed detonated; clutter is abundant, and its sensor responses are often similar to comparably sized UXO. Necessarily conservative practices to date ensure an enormous false alarm rate, and thus cleanup costs are very high.

    Against this background, recent developments provide a heartening story; the particulars are engaging, and there is a happy ending. Spanning the last ten or fifteen years, the narrative proceeds over a continuum of all aspects of the problem:

    • head scratching over fundamental physics and phenomenology;
    • new, successful modeling and analysis methods;
    • informative and reassuring engagements of those methods with data;
    • design, development, and testing of new instruments that provide expanded and superior data;
    • innovative processing techniques that draw on both the modeling and the instrumentation developments; and, finally,
    • highly successful discrimination performance in blind field tests at standardized sites.

    Successes notwithstanding, many challenges remain, and much work remains to be done. Formidable settings abound, such as rugged, vegetated terrain, wetlands, and underwater sites. Although this book cannot answer the entire set of problems, it furnishes a firm base in productive threads of development, thus fostering realistic inspiration to proceed. It is designed for lay scientists and engineers, as well as for specialists in the area, and is relatively self-contained. That is, it requires no more than an acquaintance with basic vector calculus and matrix methods, common statistical concepts, simple manipulations of complex variables, and some familiarity with elementary physics. Explanations and arguments proceed from fundamentals; the grasp of the state of the art that this provides may not be as nuanced as possible, but it should be secure.

    The subject of this Tutorial Text comprises not one but many constituent topics because contributions from many diverse fields must be synthesized to produce a complete treatment of the problem, i.e., discrimination as opposed to detection of buried UXO. The latter enterprise is preoccupied with whether or not sensors can "see" the UXOs at all and whether survey practices and technology register all of them. By contrast, discrimination seeks to distinguish those registered signal anomalies that correspond specifically to UXOs from those that do not. A thorough treatment of everything that must be woven together to accomplish discrimination would easily overwhelm an introductory book such as this (cf. the number and variety of aspects in the recitation above). Instead, this text focuses on what is most peculiar to UXO discrimination, on the features of contributing areas that are most relevant, and on the basic concepts in disciplines or tools that are indispensable. The intention is to provide at least a broad review in each area that has shown itself to be vital, along with references that should enable deeper pursuit. That said, the text minimizes line by line, item by item references as the explanations proceed to maintain more appropriate flow for what is, after all, a tutorial. A list of references appears at the end of each chapter; apologies are offered to the many colleagues who have contributed so notably to the field but who may feel that the specifics of their work have not been adequately highlighted.

    On a personal level, I must express special thanks to my sources of material support over the years and to the groups of engaging individuals with whom I worked at a variety of institutions. In the very least, those entities include the Army Corps of Engineers ERDC (Engineer Research and Development Center); the DOD-EPA-DOE joint programs on Strategic Environmental Research and Development (SERDP) and Environmental Security Technology Certification (ESTCP); the Thayer School of Engineering at Dartmouth College; the Center for Electromagnetic Theory and Applications at MIT; Geophex, Ltd.; G&G Sciences, Inc.; the ElectroScience Laboratory at Ohio State University; and the Geophysical Inversion Facility at the University of British Columbia. The most special appreciation goes to my wife, Suzanne, who has no technical involvement in the field but who, for me, makes everything possible and worthwhile.

    Kevin O'Neill
    November 2015

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