Unexploded Ordnance Detection Research Articles

Mutual induction and the effect of host conductivity on the EM induction response of buried plate targets using 3-D finite-element analysis

A finite-element analysis of electromagnetic induction (EMI) in the presence of multiple buried metal targets is undertaken for the purpose of unexploded ordnance (UXO) detection and discrimination. The effects of mutual coupling between metal targets and the host conductivity are shown to be important. At high frequencies, mutual coupling is strong, and effects of host conductivity are relatively minor. At lower frequencies near the resistive limit, EMI responses are very small, but the effect of host conductivity becomes important. This is due to the galvanic current flow in the host medium that dissipates charge accumulations on the host/target interfaces. Qualitative analysis of induced current patterns in metal targets demonstrates that mutual coupling is strongly affected by target orientation and skin depth. Rigorous forward modeling of EMI responses is essential to understanding UXO sensor signatures so that discrimination between live UXO items and harmless fragments and clutter may become possible.

Reducing tensor magnetic gradiometer data for unexploded ordnance detection

Abstract Robert E. Bracken and Philip J. Brown of the US Geological Survey describe ongoing work on a tensor magnetic gradiometer system being designed for use in the detection of buried unexploded ordnance.

Environmental Applications of Sub-Audio Magnetics

Sub-Audio Magnetics (SAM) is a method by which a total-field magnetic sensor may be used to simultaneously acquire both total magnetic intensity (TMI) and total-field electromagnetic induction (TFEMI) responses from buried metal. In situations where public safety is involved, regulators, such as the U.S. Environmental Protection Agency, can mandate the use of both magnetic and electromagnetic sensors for the detection of potentially hazardous items such as unexploded ordnance (UXO) and metal drums. SAM has now completed a program of evaluation and certification as a state-of-the-art technology, acceptable for application in the litigation-sensitive environmental hazard remediation market.During its certification program, SAM was applied to controlled U.S. test sites at the Aberdeen Proving Ground, Maryland, McKinley Range, Alabama, Waikoloa, Hawaii, and at the Newholme facility in Australia. It was also applied to situations in Montana where live UXO was present. In these demonstrations, a direct comparison was made between SAM results and common, state-of-the-art alternative geophysical detecting technologies. Based on demonstrations at these sites, it has been possible to quantify the key performance parameters: level of effort, detection performance as a function of depth and target size, false-alarm rejection achieved through dual-mode sensing, and the cost-benefit ratio of SAM compared with contemporary sensor technologies such as the Geonics EM61 and EM63 electromagnetic detectors, and G-tek’s TM-5EMU electromagnetic detector and TM-4 total field magnetometer.SAM has proven to be very successful in detecting a wide range of metallic UXO items to depths exceeding achievable detection by all contemporary sensors. In the Montana live sites, where the smallest item of UXO was a 76 mm projectile, false-alarm rates were reduced from 7 per UXO, using TMI only, to 0.7 per UXO using combined SAM TMI and TFEMI data, without diminishing the probability of UXO detection. Survey cost per hectare using SAM was determined to be less than one quarter that of conducting TMI plus EMI surveys separately.The application of SAM to extremely magnetic lava flows at Waikoloa in Hawaii showed that SAM cannot yet compete with the ground-balancing capability of the TM-5EMU in this environment. Advanced signal-processing development may reduce this present limitation.

Developing geophysical techniques for detecting unexploded ordnance

John M Stanley, chief technology officer, and Malcolm K Cattach, director, research and development division, of Australian company Geophysical Technology (G-tek) reflect on the increasing demand for cost effective detection of unexploded ordnance. The problem of buried hazard remaining from unexploded ordnance (UXO) has been with us since the first use of explosives in ordnance. During the major twentieth century conflicts, it was not uncommon for the failure rate in explosive ordnance to be as high as 20%, resulting in a very large number of these weapons remaining in the ground long after the conflict ceased. These weapons are still causing injury, death and damage when disturbed or when their contents leak into the groundwater system. UXO also provide a potential source of explosives for terrorist interests. In addition to UXO remaining from conflict, a major source of environmental contamination has been military training activity. To put some perspective on the extent of this problem, the office of the Secretary of US Defense reported: ‘The UXO clean-up problem is a very large-scale undertaking involving 10 million acres of land at some 1400 sites. Estimated cleanup cost of current UXOs is tens of billions of dollars’. The problem is not confined to the US. It is generally believed that matters are worse in Eastern Europe than in the US. It is unlikely that there is a country in the world where contamination and explosive hazard from UXO does not exist. Detecting the presence of UXO in the ground presents a task for which geophysicists familiar with the characteristics of the near-surface environment are well equipped. Moreover, the geophysical community involved in the UXO industry is now setting standards of quality procedure from which our colleagues in oil, gas and minerals exploration may well learn. Since when has an exploration geophysicist been held responsible for not finding a resource that current technology was capable of detecting?

Analysis of Correlated Noise in Airborne Magnetic Gradients for Unexploded Ordnance Detection

In this paper, we examine several field tests of correlated helicopter noise and demonstrate that measured vertical gradients can offer signal-to-noise improvements of 4:1 in rotor noise and 6:1 in maneuver noise over comparable total field measurements for unexploded ordnance (UXO) applications. This translates into an additional [Formula: see text] in acceptable survey height or ordnance depth. Horizontal gradients, both transverse and longitudinal to the helicopter flight path, are also examined. These offer smaller signal-to-noise improvements over the total field (approximately 1.5:1) and have other disadvantages not found in the vertical gradient.

Report on a workshop on electromagnetic induction methods for UXO detection and discrimination

To decrease cost and increase reliability and efficiency of unexploded ordnance (UXO) environmental remediation, government research and development programs and industry efforts seek to establish a practice of UXO location using modern digital survey systems, sound geophysical survey procedures, and postprocessing of data for enhanced detection and discrimination. The new practice will replace most traditional “mag and flag” type UXO location surveys that typically use analog instruments, where all detected targets (anomalies) must be investigated (i.e., excavated). Several factors, both technical and nontechnical, drive and justify the change in practice: (1) digital data allow maintenance of a permanent record of the locations of targets and sensor signatures over targets; (2) digital data will typically have higher dynamic range (hence higher signal-to-noise ratios) than the analog data that rely on audio or visual output; (3) digital data allow and facilitate postprocessing to enhance signatures for ...

Image segmentation based on competitive learning

Image segment is a primary step in image analysis of unexploded ordnance (UXO) detection by ground penetrating radar (GPR) sensor which is accompanied with a lot of noises and other elements that affect the recognition of real target size. In this paper we bring forward a new theory, that is, we look the weight sets as target vector sets which is the new cues in semi-automatic segmentation to form the final image segmentation. The experiment results show that the measure size of target with our method is much smaller than the size with other methods and close to the real size of target.

Field tests of an experimental helicopter time‐domain electromagnetic system for unexploded ordnance detection

Field trials of a low‐flying time‐domain helicopter electromagnetic system designed for detection of unexploded ordnance have yielded positive and encouraging results. The system is able to detect ordnance as small as 60‐mm rounds at 1‐m sensor height. We examined several transmitter and receiver configurations. Small loop receivers gave superior signal‐to‐noise ratios in comparison to larger receiver loops at low heights. Base frequencies of 90 Hz and 270 Hz were less affected than other base frequencies by noise produced by proximity to the helicopter and by vibration of the support structure. For small ordnance, a two‐lobed, antisymmetric transmitter loop geometry produced a modest signal‐to‐noise enhancement compared with a large single rectangular loop, presumably because the antisymmetric transmitter produces smaller eddy currents in the helicopter body, thereby reducing this source of noise. In most cases, differencing of vertically offset receivers did not substantially improve signal‐to‐noise ratios at very low sensor altitudes. Signal attenuation from transmitter to target and from target to receiver causes signals from smaller ordnance to quickly become indistinguishable from geological background variations, so that above a sensor height of about 3 m only large ordnance items (e.g., bombs and large caliber artillery rounds) were consistently detected.

Simulation of Near-Surface Detection of Objects in Layered Media by the BCGS–FFT Method

Near-surface electromagnetic characterization of objects buried in multilayered earth is important for the detection and identification of landmines, unexploded ordnance, and underground structures. However, so far little progress has been made in the development of fast algorithms for inhomogeneous objects in a layered medium. We report an iterative technique, the stabilized biconjugate gradient fast Fourier transform (BCGS-FFT) method, that simulates near-surface detection of three-dimensional, inhomogeneous objects buried in multilayered media. The CPU time and memory cost of the BCGS-FFT method is O(NlogN) and O(N), respectively, where N is the number of unknowns. This method is significantly more efficient than method of moments. It is capable of solving large-scale electromagnetic scattering problems with an arbitrary inhomogeneous object embedded in a layered medium with an arbitrary number of layers. Examples in subsurface detection of large buried objects are shown to demonstrate the efficacy of this method. At present, the object must be located completely within one single layer in this multilayer medium, but efforts are underway to remove this limitation.

Near-surface Ground Penetrating Radar Imaging Algorithms

SummaryIn recent years the accurate detection of near-surface buried objects has attracted considerable attention from the remote sensing community. One of the more promising sensors for this problem is Ground Penetrating Radar (GPR). This sensor has been applied to many problems including ore detection, locating pipes and conduits, waste remediation, landmine and unexploded ordnance detection, archaeologically surveying and non-destructive testing. Many algorithms exist which attempt to detect near-surface buried objects from GPR data. Some of these algorithms rely on expert interpretation of the collected data while others attempt to match the radar return to a database of known object returns. The ideal algorithm, however, will provide accurate images of the subsurface by reconstructing the electrical properties (permittivity and conductivity) of the buried scatterers and their ambient soil. Such an algorithm will provide the user with a three-dimensional image of the ground’s permittivity and/or conductivity, from which objects may be easily identified. This review will focus upon algorithms which attempt to provide this ideal means of detection and will clearly identify how each algorithm differs from the ideal.

Implications of magnetic backgrounds for unexploded ordnance detection

Detection of buried unexploded ordnance (UXO) requires application of geophysical methods that exploit contrasts in magnetic susceptibility and/or electrical conductivity of the UXO relative to surrounding soil and rock (the geologic background). At many sites, the contrasts are very large, and the detection capability is relatively independent of the geologic background. Some sites, however, are predictably problematic, such as volcanic terrains (e.g., Maui and Kaho'olawe, HI, USA). Other sites that would not intuitively be predicted to pose detection problems are found to have localized high susceptibility zones with wavelengths and magnitudes that can significantly complicate UXO detection. Details of a site in Indiana (USA) are presented that illustrate order of magnitude variation of magnetic susceptibility over distances of 2–3 m. Magnetic susceptibility at the site correlates to topography and soil type. Magnetic power spectral density plots from magnetic surveys at selected areas at the Indiana site are compared to each other and to data from Maui, HI, and demonstrate the key issues in UXO detection with magnetometry. Magnetic susceptibility data from Kaho'olawe are used to illustrate the effects on electromagnetic induction surveys for UXO detection and discrimination. The phenomenological observations suggest approaches for magnetic and electromagnetic induction survey data processing to enhance anomaly detectability and model-based inversion.

Dramatic Improvements in UXO Detection Using Discrimination and Dual-Mode Sensor Technology

"Dramatic Improvements in UXO Detection Using Discrimination and Dual-Mode Sensor Technology." ASEG Extended Abstracts, 2003(2), p. 1

Unexploded ordnance detection using Bayesian physics-based data fusion

Detection of unexploded ordnance (UXO) represents a major challenge on closed, closing, and transferred military ranges as well as on active installations. On sites contaminated with UXO, extensive surface and sub-surface clutter is also present. Tra

Sensing of unexploded ordnance with magnetometer and induction data: theory and signal processing

We consider the detection of subsurface unexploded ordnance via magnetometer and electromagnetic-induction (EMI) sensors. Detection performance is presented, using model-based signal processing algorithms. We first develop and validate the parametric models, using both numerical and measured data. These models are then applied in the context of feature extraction, and the features are processed via two signal-processing algorithms. The detection algorithms are discussed in detail, with comparisons made based on performance with measured magnetometer and EMI data.

Wide-area detection of land mines and unexploded ordnance

Advanced electromagnetic modelling tools are discussed, focused on sensingsurface and buried land mines and unexploded ordnance, situated in a realisticsoil environment. The results from these forward models are used to processscattered-field data, for target detection and identification. We address sensorsdirected toward the wide-area-search problem, for which one is interested indetecting a former mine field or bombing range. For this problem class we processdata measured from an actual airborne radar system. Signal-processing algorithmsapplied include Bayesian processing and a physics-based hidden Markov model.

Microwave underground propagation and detection

The detection of buried targets has been a problem of significant interest for decades, with microwave-based sensing constituting an important tool. In this paper, we review the basic issues that characterize microwave-based subsurface sensing. Issues considered include the use of microwaves in the context of an airborne synthetic aperture radar, as well for radars deployed close to the air-soil interface. Rough-surface induced clutter is also discussed. Particular examples are presented for detection of land mines and unexploded ordnance.

US Air Force EarthRadar for detection and discrimination of buried unexploded ordnance

The US Air Force EarthRadar system is a multi-purpose sensor designed and constructed using radar principles. This technology was originally developed for the US Air Force to detect buried unexploded ordnance (UXO). Bakhtar Associates developed the US Air Force EarthRadar technology under the DoD SBIR program. The system is capable of detecting buried metallic and non-metallic objects, including glass vials. In addition, the manner in which system hardware, signal processing, and the integrated high resolution global positioning system (GPS) are configured makes it ideal for applications such as mapping subsurface geological features, locating cavities and collapse features, and identifying contaminated ground.

Multi-aspect detection of surface and shallow-buried unexploded ordnance via ultra-wideband synthetic aperture radar

An ultra-wideband (UWB) synthetic aperture radar (SAR) system is investigated for the detection of former bombing ranges, littered by unexploded ordnance (UXO). The objective is detection of a high enough percentage of surface and shallow-buried UXO, with a low enough false-alarm rate, such that a former range can be detected. The physics of UWB SAR scattering is exploited in the context of a hidden Markov model (HMM), which explicitly accounts for the multiple aspects at which a SAR system views a given target. The HMM is trained on computed data, using SAR imagery synthesized via a validated physical-optics solution. The performance of the HMM is demonstrated by performing testing on measured UWB SAR data for many surface and shallow UXO buried in soil in the vicinity of naturally occurring clutter.

Multisensor towed array detection system for UXO detection

The multisensor towed array detection system (MTADS) was designed to be an efficient, sensitive tool for the detection and characterization of buried unexploded ordnance. It comprises arrays of total-field magnetometers and time-domain electromagnetic induction (EMI) sensors, associated navigation and data acquisition hardware, and a custom data analysis system. The MTADS has conducted eleven demonstrations and surveys. The system has shown the ability to detect ordnance at its likely self-penetration depths with a probability of detection of 0.95 or better The model-derived positions and depths of the detected ordnance items are generally well within the physical size of the targets, making remediation much quicker and less costly than with standard techniques. Data sets corresponding to many of the MTADS surveys are available to others in the field.

Acoustic landmine detection: Poroelastic model and elastic wave models

Acoustic waves can be a viable tool for the detection and identification of landmines and unexploded ordnance (UXO). Design of acoustic instruments and interpretation and processing of acoustic measurements require accurate numerical models for acoustic wave propagation in heterogeneous soil with buried objects. Two numerical models will be compared in this work: the soil is treated as an elastic material in the first model, and as a poroelastic material in the second model. A multidomain pseudospectral time-domain method is used for the elastic model, while a finite-difference method is used to solve Biot equations in the poroelastic model. Acoustic wave response of a buried landmine is investigated with both methods. When the soil is treated as a fluid-saturated poroelastic medium, additional attenuation is automatically introduced via the relative motion between solid frame and pore fluid. Thus the poroelastic model is presumably a more accurate model; however, the elastic model requires less computation time. This work will study several important scenarios such as landmines buried in dry sand, in wet sand, and in mud. A comparison between results of the PSTD model and results of the poroelastic model is performed to characterize the regime of validity for the elastic model.