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Identification of Metallic Spheroids by Classification of Their Electromagnetic Induction Response
... If the number of objects under consideration is finite, we may consider pattern recognition. A method which has been successfully used to classify metallic spheroids [79] will be described as an example. As previously stated, once we have localized the object, the coil axes are approximately over its geometric center. ...
... The segments do not have to be equal time intervals but may be adjusted for constant energy (area). There are advantages and disadvantages for each feature 'type which are beyond the scope of this course (see [79] for a discussion). A simple, but quite successful choice [79] has been the mean response for each segment with equal time intervals. ...
... There are advantages and disadvantages for each feature 'type which are beyond the scope of this course (see [79] for a discussion). A simple, but quite successful choice [79] has been the mean response for each segment with equal time intervals. A feature vector for a response then consists of the sequence of fit parameters for all segments. ...
A series of lectures are presented on the topic of the location and identification of compact objects by low frequency electromagnetics. These lectures were presented as a portion of two graduate level courses in electrical engineering at the University of Toronto in 1985 and 1987. magnetostatics, electrostatics and electromagnetic induction techniques are discussed in detail. Keywords: Magnetic, Canada, Remote sensing, Detectors, Magnetostatics, Electromagnetic detectors, Electromagnetic induction, Electrostatics, Compact, Object, Detection, Location, Identification, Quasiremote, Remote sensing.
... The secondary field depends on many factors: the conductivity and permeability of the object and of the background, the size and the shape of the object, its geometry (distance, orientation) and the temporal and spatial distribution of the primary field [23]. It can be shown that the influence of the target's dielectric properties are negligible in the frequency range used by mine searching metal detectors, which is between 1 and 100 kHz [16]. ...
This thesis proposes a design of experiment for testing and evaluation of the equipment and the methods used in manual mine clearance. The thesis is based on several metal detector trials and a trial of manual demining methods. The core of this dissertation comprises four metal detector trials performed in Germany and Croatia in 2003 and 2005. The purpose of these trials was to investigate the feasibility of the tests described in the CWA (Comit´e Europ´een de Normalisation /CEN/ Workshop Agreement) 14747:-2003, the standard for testing metal detectors for humanitarian demining. The goals of the trials were: to find an appropriate design of experiment for testing metal detectors; to establish the use of ROC diagrams (Receiver Operating Characteristics) and POD curves (Probability of Detection) in the analysis of the experimental results; and to gain practical experience in organising and conducting metal detector trials. A part of this thesis is devoted to a trial of manual demining methods performed in Mozambique in 2004. The main goal of that trial was to compare the speed of various manual demining methods, including the most common excavation methods. The outcome of this work are the proposals and recommendations for an update of the standard for testing metal detectors CWA 14747:2003. Maximum detection height measurements were performed as a part of the metal detector trial carried out in Croatia in 2005. The results reveal a high variability of the maximum detection height. This high variability needs to be taken into account in all experiments. A part of the variability is caused by the differences between the operators and by the setup of the metal detector. It is therefore recommended that two kinds of experiments with the maximum detection height as a response variable are defined in the next update of CWA 14747:2003. The first kind should include the setup, the soil and the operator as factors in the design of experiment. The in-soil measurements with the same detector should be performed with repeated setups and with several operators. The second kind of experiments should be experiments evaluating the influence of other predictor variables. In those experiments, it is recommended to perform one-factor or multiple-factor in-air measurements with the operators and the setup as a block. The main part of the metal detector trials described in this thesis were the detection reliability tests. Detection reliability tests as described in CWA 14747:2003 come closest to representing the real field conditions in demining. They include many environmental influences and, most importantly, many of the human factor influences. However, each test design is a compromise between fully representative conditions and cost effectiveness. In this thesis, a fractional factorial design based on the Graeco-Latin square is proposed as a solution to the experimental problem. The results are reported in the form of ROC diagrams and POD curves. The crossover design enables each operator to work with fewer detector models within a certain time. The variations of the design enabled an unbiased comparison of detectors in each soil and with each target model separately. It is recommended that the solutions proposed in this thesis be incorporated in the standard CWA 14747:2003. It has been shown that maximum detection height measurements provide the information about the best possible performance of a metal detector in a reliability test.
... The role of pattern recognition methods such as machine learning and target feature extraction, as an alternative to inversion, is gaining rapid acceptance in areas such as unexploded ordnance (UXO) and landmine detection. An important early paper in classification of buried spheroids by their CSEM response is by Chesney et al. (1984). It would be interesting to explore whether such concepts can be applied to hydrogeophysical settings in which the subsurface target is not necessarily an isolated, well-defined man-made object but instead could be a subtle, finely-distributed and irregular variation in the subsurface electrical conductivity distribution. ...
... The design set for an object consisted of the feature vectors for all orientations (15' increments) at a given depth. A continuous parameter pattern classifier [19], similar to the one used in magnetostatics, was able to classify the objects with a probability of misclassification of about 1% if the design and test sets were obtained for the same object depth. If the two sets were taken from depths differing by 0.1 m, the probability increased to about 11%. ...
... The role of pattern recognition methods such as machine learning and target feature extraction, as an alternative to inversion, is gaining rapid acceptance in areas such as unexploded ordnance (UXO) and landmine detection. An important early paper in classification of buried spheroids by their CSEM response is by Chesney et al. (1984). It would be interesting to explore whether such concepts can be applied to hydrogeophysical settings in which the subsurface target is not necessarily an isolated, well-defined man-made object but instead could be a subtle, finely-distributed and irregular variation in the subsurface electrical conductivity distribution. ...
The controlled-source electromagnetic (CSEM) induction method is emerging as a leading geophysical technique in hydrogeological
studies. However, the technique is quite often misunderstood compared to other common techniques of applied geophysics: namely,
seismic reflection and refraction, magnetics, gravity, and ground-penetrating radar (GPR). In this chapter we review the fundamental
physical principles behind the CSEM prospecting technique, with emphasis on near-surface applications, and present some recent
advances in this field that have been made by the authors. CSEM methods are defined here to be those in which the experimenter
has knowledge of and control over the electromagnetic field transmitted into the ground and hence excludes magnetotellurics,
related natural-source methods, and the various uncontrolled-source methods involving, for example, radio transmissions.
... The "ground truth" model, for the scattering characteristics of these targets, was obtained using the method of [36], where the dipole model was taken to be exact. Four terms were kept in each λ i summations in (4), and all expansion coefficients were taken to be one (see [36] for additional details). ...
We consider the problem of classifying buried objects using electromagnetic induction data collected in a setting where there are errors in sensor positioning. Using a series of decay constants (or equivalently, Laplace plane poles) as features for classification, our algorithm seeks to estimate these poles and, subsequently, to determine the type of object in the sensor field of view. In many practical scenarios, a set of data is often accompanied by domain knowledge that the location of the transmitters and/or receivers is only known to within some degree of accuracy (e.g., 10 cm in the along-track direction and 5-cm cross-track). Here, we develop an approach to the extraction of information from such data sets in which the quantitative positional bound information is used in the context of a min-max optimization strategy. Specifically, we look for the parameters of interest that minimize the maximum data residual, where the maximum error is computed over ellipsoids or polyhedra of possible sensor locations defined by the bound information. Our formulation admits data collection with independent or dependent positional uncertainty values at successive nominal collection locations. Our algorithms for solving this optimization problem are validated using simulated and measured data
The EPFL and the VUB have been investigating the response of metal detectors within the framework of humanitarian demining research activities, in particular frequency domain systems. A simple circuit model has bene looked at first, followed by the analysis of a more completed model. As has also been stressed before, this analysis indicates the possibility of identifying some metallic objects. In addition the phase shift of the received signal turns out to be a continuous, monotonically decreasing function of the object size; this leads to the idea of imposing a 'phase threshold' in order to reduce the amount of detected clutter. This discrimination-based approach is less ambitious than object identification, but is likely to be more robust and to work when looking for metallic objects of a certain size, e.g. non minimum-metal mines or UXO. A first series of measurements was therefore carried out using a commercially available, differential tow frequent metal detector, the Foerster MINEX 2FD. The detector's internal signals have been recorded in a laboratory setup along linear scans varying different object parameters for several representative objects. The collection of data as a function of movement enables the possibility of analyzing the data in the complex plane, and makes it possible to exploit global object properties. Some representative results are presented and the limits of such discrimination/identification approaches briefly outlined.
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