Electromagnetic detection of buried metallic objects using quad–quad conductivity

Geophysics ◽  
2004 ◽  
Vol 69 (6) ◽  
pp. 1387-1393 ◽  
Author(s):  
Haoping Huang ◽  
I. J. Won
Keyword(s):  
Magnetic Susceptibility ◽  
Rough Terrain ◽  
Unexploded Ordnance ◽  
Magnetic Polarization ◽  
Phase Component ◽  
Apparent Conductivity ◽  
Electromagnetic Detection ◽  
Phase Data ◽  
Magnetic Soil

Apparent conductivity computed from in‐phase and quadrature components has been used successfully to detect buried metallic objects such as unexploded ordnance (UXO). The conductivity computation uses magnetic susceptibility calculated from the lowest‐frequency in‐phase data obtained at a specific sensor height. Over magnetic soils, however, the in‐phase component may fluctuate with varying sensor heights. Uncertainties in sensor height, common with handheld or cart‐mounted sensors in rough terrain, can produce errors in the computed magnetic susceptibility, which, in turn, causes errors in apparent conductivity. To overcome these limitations, we have developed an algorithm to compute the quad–quad apparent conductivity from the quadrature components at two frequencies. Our results show that the quad–quad technique has several advantages for detecting metal targets in magnetic terrains: it is (1) insensitive to the magnetic polarization currents; (2) it is immune to sensor motion over magnetic soil; and (3) it is biased to metal objects and can detect small and/or deep metal targets. The first two properties suppress the noise caused by magnetic terrain and sensor motion and thus yield a quiet background. The last property emphasizes metal objects as sought anomalies over geologic variations.

Automated anomaly picking from broadband electromagnetic data in an unexploded ordnance (UXO) survey

Geophysics ◽  
2003 ◽  
Vol 68 (6) ◽  
pp. 1870-1876 ◽  
Author(s):  
Hoaping Huang ◽  
I. J. Won
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Field Data ◽  
Real Data ◽  
False Alarms ◽  
Rough Terrain ◽  
Unexploded Ordnance ◽  
Electromagnetic Data ◽  
Apparent Conductivity ◽  
Using Data

We present automated anomaly‐picking methods for detecting unexploded ordnance (UXO) from broadband electromagnetic (EM) data. Using data consisting of in‐phase and quadrature responses at multiple (typically 10) frequencies, a detector function attempts to detect all metal objects but to suppress false alarms caused by geology, variations in sensor height, and sensor motions in the earth's magnetic field. Promising detector functions considered here are (1) the sum of all quadrature responses, Qsum, (2) the sum of all differences among the in‐phase or quadrature components, Ispread or Qspread, (3) the sum of the Ispread and Qspreads, Tspread, (4) the weighted total apparent conductivity (TAC) from all frequencies, and (5) the apparent magnetic susceptibility (AMS) derived from the lowest frequency of a survey. These detector functions favor metallic objects and are relatively insensitive to geologic variations and motion‐induced noise, which are common with a handheld or cart‐mounted sensor in rough terrain. We discuss the properties of these detector functions, apply them to field data from two sites, and compare the results with limited ground truths. Based on the theoretic study and test on the real data, the total apparent conductivity is the best detector function for picking and classifying anomalies, which shows more distinct anomalies and quieter background than other detector functions.

Anisotropy of out-of-phase magnetic susceptibility due to eddy currents in graphite ore and its structural implications

2021 ◽  
Author(s):  
František Hrouda ◽  
Jan Franěk ◽  
Martin Chadima ◽  
Josef Ježek ◽  
Štěpánka Mrázová ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Eddy Currents ◽  
Regional Metamorphism ◽  
Ductile Deformation ◽  
Dynamic Susceptibility ◽  
Phase Component ◽  
Simultaneous Control ◽  
Order Of Magnitude ◽  
Moldanubian Unit ◽  
Sufficient Precision

<p>Magnetostatic susceptibility of single crystals of graphite is negative (the mineral is diamagnetic) and strongly anisotropic. The in-phase component of dynamic susceptibility (measured in alternating magnetic field) is also negative, but an order-of-magnitude stronger than the magnetostatic susceptibility. The out-of-phase component, which is no doubt due to electrical eddy currents, is positive and strong. Consequently, if the graphite crystals in graphite ore are oriented preferentially by crystal lattice (LPO), one would expect strong anisotropy of magnetic susceptibility (AMS) of graphite ore in both in-phase (ipAMS) and out-of-phase (opAMS) components. The ipAMS is controlled not only by the LPO of graphite, but also by the preferred orientation of paramagnetic and ferromagnetic minerals of the barren rock, while the opAMS indicates only the LPO of graphite. In graphite ores occurring in the Moldanubian Unit of Southern Bohemia, the in-phase susceptibility ranges from negative values in the order of 10<sup>-5</sup> [SI units] to positive values in the order of 10<sup>-4</sup>. This probably indicates simultaneous control by graphite and paramagnetic and/or ferromagnetic minerals. On the other hand, the out-of-phase susceptibility is much higher, in the order of 10<sup>-4</sup>, and no doubt indicates its graphite control. The degree of ipAMS is moderate, that of opAMS is truly high. The ipAMS foliation is roughly parallel to the metamorphic foliation in ores and wall rocks and the ipAMS lineation is parallel to the mesoscopic lineation. The opAMS is inverse to the ipAMS with the opAMS lineation being perpendicular to the metamorphic foliation. All this indicates a conspicuous LPO of graphite in the ore that was probably created during Variscan regional metamorphism and associated ductile deformation. The opAMS has therefore shown an effective tool for the investigation of the LPO of graphite in graphite ore or graphite-bearing rocks provided that the opAMS is strong enough to be determined with sufficient precision and graphite is the only conductive mineral in the samples investigated.</p>

Inversion of ground constant offset loop-loop electromagnetic data for a large range of induction numbers

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. E11-E21 ◽  
Author(s):  
Julien Guillemoteau ◽  
Pascal Sailhac ◽  
Charles Boulanger ◽  
Jérémie Trules
Keyword(s):  
Synthetic Data ◽  
Test Site ◽  
Maxwell Theory ◽  
Data Set ◽  
Electromagnetic Data ◽  
Apparent Conductivity ◽  
Airborne Electromagnetic ◽  
Phase Data ◽  
Ground Conductivity ◽  
Good Agreement

Ground loop-loop electromagnetic surveys are often conducted to fulfill the low-induction-number condition. To image the distribution of electric conductivity inside the ground, it is then necessary to collect a multioffset data set. We considered that less time-consuming constant offset measurements can also reach this objective. This can be achieved by performing multifrequency soundings, which are commonly performed for the airborne electromagnetic method. Ground multifrequency soundings have to be interpreted carefully because they contain high-induction-number data. These data are interpreted in two steps. First, the in-phase and out-of-phase data are converted into robust apparent conductivities valid for all the induction numbers. Second, the apparent conductivity data are inverted in 1D and 2D to obtain the true distribution of the ground conductivity. For the inversion, we used a general half-space Jacobian for the apparent conductivity valid for all the induction numbers. This method was applied and validated on synthetic data computed with the full Maxwell theory. The method was then applied on field data acquired in the test site of Provins, in the Parisian basin, France. The result revealed good agreement with borehole and geologic information, demonstrating the applicability of our method.

Detecting metal objects in magnetic environments using a broadband electromagnetic method

Geophysics ◽  
2003 ◽  
Vol 68 (6) ◽  
pp. 1877-1887 ◽  
Author(s):  
Haoping Huang ◽  
I. J. Won
Keyword(s):  
Magnetic Permeability ◽  
Field Studies ◽  
Unexploded Ordnance ◽  
Apparent Conductivity ◽  
Physical Experiments ◽  
Detection And Identification ◽  
Em Method ◽  
Magnetic Basement ◽  
Quadrature Response ◽  
Layered Half Space

We analyze the use of the broadband electromagnetic (EM) method in detecting metallic objects, such as unexploded ordnance (UXO), buried in magnetic environments. Magnetic rocks close to the sensor often contribute a larger in‐phase response than does the target at depth, making target detection and identification difficult. On the other hand, magnetic rocks contribute little quadrature response, which gives rise to the concept of using quadrature response and apparent conductivity to detect metallic objects in highly magnetic environments. To test this concept, we employed numeric models, physical experiments, and field studies. A layered half‐space simulated conductive overburden and magnetic basement. Sphere models are used for isolated magnetic rocks and metal targets. The responses of the layered earth, magnetic rocks, and metal objects were added to obtain the approximate total response. We then inverted the EM data into apparent magnetic permeability and conductivity. The EM response at the lowest frequency was used initially to estimate apparent magnetic permeability, which let us calculate the apparent conductivity using the EM data at all frequencies. The simulations and field examples show that broadband EM sensors can detect small metal targets in magnetic environments, mainly by the quadrature component of the responses and the apparent conductivity.

scholarly journals DeepQSM - Using Deep Learning to Solve the Dipole Inversion for MRI Susceptibility Mapping

2018 ◽  
Author(s):  
Kasper Gade Bøtker Rasmussen ◽  
Mads Kristensen ◽  
Rasmus Guldhammer Blendal ◽  
Lasse Riis Østergaard ◽  
Maciej Plocharski ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Magnetic Susceptibility ◽  
Iron Homeostasis ◽  
Nerve Fibers ◽  
Susceptibility Mapping ◽  
Source Inversion ◽  
Tissue Properties ◽  
Ill Posed ◽  
Phase Data

Quantitative susceptibility mapping (QSM) aims to extract the magnetic susceptibility of tissue from magnetic resonance imaging (MRI) phase measurements. The mapping of magnetic susceptibility in vivo has gained broad interest in several fields of science and medicine because it yields relevant information on biological tissue properties, predominantly myelin, iron and calcium. Thereby, QSM can also reveal pathological changes of these key components in devastating diseases such as Parkinson’s disease, Multiple Sclerosis, or hepatic iron overload. As QSM requires the solution of an ill-posed field-to-source-inversion, current techniques utilize manual optimization of regularization parameters to balance between smoothing, artifacts and quantification accuracy. We trained a fully convolutional deep neural network - DeepQSM - to invert the magnetic dipole kernel convolution. This network is capable of solving the ill-posed field-to-source inversion on real-world in vivo MRI phase data without the need for manual parameter tuning, which proves that this network has generalized the underlying mathematical principle of the dipole inversion. We demonstrate that DeepQSM’s susceptibility maps enable identification of deep brain substructures that are not visible in MRI phase data and provide information on their respective magnetic tissue properties. We illustrate DeepQSM’s clinical relevance in a patient with multiple sclerosis showing its sensitivity to white matter lesions. In summary, DeepQSM can be used to determine the composition of myelin sheets of nerve fibers in the brain, and to assess quantitative information on iron homeostasis and its dysregulation, and will subsequently contribute to a better understanding of these biological processes in health and disease.

scholarly journals Magnetic susceptibility mapping of brain tissue in vivo using MRI phase data

2009 ◽  
Vol 62 (6) ◽  
pp. 1510-1522 ◽  
Author(s):  
Karin Shmueli ◽  
Jacco A. de Zwart ◽  
Peter van Gelderen ◽  
Tie-Qiang Li ◽  
Stephen J. Dodd ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Brain Tissue ◽  
Susceptibility Mapping ◽  
Phase Data

Some Issues in Magnetic Measurement of Mass Standards

2013 ◽  
Vol 631-632 ◽  
pp. 837-841 ◽  
Author(s):  
Xiao Ping Ren ◽  
Jian Wang ◽  
Rui Lin Zhong ◽  
Chang Qing Cai ◽  
Yue Zhang
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Measurement ◽  
Magnetic Interactions ◽  
Comparison Process ◽  
Magnetic Polarization ◽  
Uncertainty Factors ◽  
Two Factors

Magnetic interactions may lead to errors in precision mass metrology. There are two factors named magnetic susceptibility and magnetic polarization which need to be determined before mass metrology. First four methods are compared and analyzed suitable range, requirement, uncertainty and note in comparison process. Then uncertainty factors are given out, and description of differences between normal weights and micro-gram standards are presented in the paper. It is easy to become magnetized if the weight is not well protected in manufacture or daily using. So it is important to control its safe and perform periodic self-verification on it.

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