Imaging of 3D electromagnetic data at low-induction numbers

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. WB47-WB57 ◽  
Author(s):  
Marco A. Pérez-Flores ◽  
Ricardo G. Antonio-Carpio ◽  
E. Gómez-Treviño ◽  
Ian Ferguson ◽  
S. Méndez-Delgado
Keyword(s):  
Synthetic Data ◽  
3D Models ◽  
Two Dimensions ◽  
Imaging Data ◽  
Magnetic Dipoles ◽  
Near Surface ◽  
Conductivity Distribution ◽  
Electromagnetic Data ◽  
Depth Discrimination ◽  
Electromagnetic Measurements

We expressed electromagnetic measurements at low induction numbers as spatial averages of the subsurface electrical conductivity distribution and developed an algorithm for the recovery of the latter in terms of the former. The basis of our approach is an integral equation whose averaging kernel is independent of the conductivity distribution. That is, the recovery of conductivity from the measurements leads to a linear inverse problem. Previous work in one and two dimensions demonstrated that using a kernel independent of conductivity leads to reasonably good results in quantitative interpretations. This study extended the approach to 3D models and to data taken along several profiles over a given area. The algorithm handles vertical and horizontal magnetic dipoles with multiple separations for appropriate depth discrimination. The approximation also handles issues like negative conductivity measurements, which commonly appear when crossing near-surface conductors. This happens particularly when using vertical magnetic dipoles; whose averaging kernel has significant negative weights in the space between the dipoles, something that does not happen for the horizontal dipoles. In general, the more complex the kernel, the more complicated the signature of any given anomaly. This makes qualitative interpretations of pseudosections somewhat difficult when dealing with more than one conductive or resistive body. The algorithm was validated using synthetic data for imaging data from horizontal or vertical coils or from a combination of them. Imaging of field data from a mine tailings site recovered a shallow 3D conductive anomaly associated with the tailings.

scholarly journals Electromagnetic Measurements for Monitoring Molybdenum Contamination in Near-Surface Survey

2015 ◽  
Vol 19 (2) ◽  
pp. 107-111 ◽  
Author(s):  
Ali Ismet Kanli ◽  
Boriszlav Neducza
Keyword(s):  
Field Study ◽  
Near Surface ◽  
Electromagnetic Data ◽  
North East ◽  
The North ◽  
Surface Survey ◽  
Susceptibility Maps ◽  
Electromagnetic Measurements ◽  
Two Stages ◽  
Depth Ranges

<p>We carried out electromagnetic measurements in the vicinity of the near surface molybdenum contamination observed in the “Blue Lagoon” plum located in the north-east of Hungary. The aim of the investigation was to find the origin of the molybdenum pollution, situated in the area, which could be a container or other infrastructure leading to the source of contamination. The field study was conducted in two stages. In the first phase, we gathered electromagnetic data by using GEM-2 type equipment. We derived conductivity and susceptibility maps for each acquired frequency from the electromagnetic data. In the second stage of the field study, GPR data were obtained from 50 MHZ and 450 MHz antennas. In the GPR measurements, we gathered detailed information from GPR depth slices from very shallow depth ranges to deeper parts of the investigated area (from 50cm to 8 m depths). In all results from the measurements executed by the GEM-2 and (50 MHZ and 450 MHz) GPR equipment, there are several clear anomalies are observed in the data for the distribution of molybdenum contamination. Although there are several contaminated zones observed, no clear evidence of the source of contamination was found in the vicinity of the molybdenum pollution peak. </p><p> </p><p> </p><p><strong>Medicione</strong>s<strong> Electromagnéticas para Rastrear la Contaminación de Molibdeno en un Estudio de Superficies</strong></p><p><strong><br /></strong></p><p><strong>Resumen</strong></p>En este estudio se llevaron a cabo mediciones electromagnéticas en las inmediaciones de un foco de contaminación de molibdeno hallado en el "Blue Lagoon", al noreste de Hungría. El propósito de la investigación fue encontrar el origen de la contaminación de molibdeno, detectada en el área, y que podría ser el contenedor u otra infraestructura que lleve a la fuente de polución. El trabajo de campo se llevó a cabo en dos partes. En la primera fase se reunió la información electromagnética a través del equipo GEM-2. De esta forma se obtuvieron mapas de conductividad y susceptibilidad para cada frecuencia adquirida de la información electromagnética. En la segunda fase del estudio de campo se obtuvieron datos del radar de penetración terrestre (GPR, en inglés) con antenas de 50 y de 450 megahercios (MHZ). En las mediciones GPR se recopiló información detallada de las muestras de penetración en un rango desde la superficie a la profundidad en el área de estudio (desde 50 cm a 8 m de profundidad). En todos los resultados de las medidas hechas con los equipos GEM-2 y GPR se encontraron varias anomalías en la distribución de datos de la contaminación por molibdeno. A pesar de que se observaron varias zonas contaminadas, no hay evidencia clara de la fuente de polución encontrada alrededor del pico de contaminación por molibdeno.</p>

Decomposition of electromagnetic fields into upgoing and downgoing components

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. G211-G223 ◽  
Author(s):  
Lasse Amundsen ◽  
Lars Løseth ◽  
Rune Mittet ◽  
Svein Ellingsrud ◽  
Bjørn Ursin
Keyword(s):  
Synthetic Data ◽  
Low Frequency ◽  
Real Data ◽  
Sea Surface ◽  
Linear Phase ◽  
Electric Permittivity ◽  
The Real ◽  
Electromagnetic Data ◽  
Electromagnetic Measurements ◽  
Em Field

This paper gives a unified treatment of electromagnetic (EM) field decomposition into upgoing and downgoing components for conductive and nonconductive media, where the electromagnetic data are measured on a plane in which the electric permittivity, magnetic permeability, and electrical conductivity are known constants with respect to space and time. Above and below the plane of measurement, the medium can be arbitrarily inhomogeneous and anisotropic. In particular, the proposed decomposition theory applies to marine EM, low-frequency data acquired for hydrocarbon mapping where the upgoing components of the recorded field guided and refracted from the reservoir, that are of interest for the interpretation. The direct-source field, the refracted airwave induced by the source, the reflected field from the sea surface, and mostmagnetotelluric noise traveling downward just below the seabed are field components that are considered to be noise in electromagnetic measurements. The viability and validity of the decomposition method is demonstrated using modeled and real marine EM data, also termed seabed logging (SBL) data. The synthetic data are simulated in a model that is fairly representative of the geologic area where the real SBL were collected. The results from the synthetic data study therefore are used to assist in the interpretation of the real data from an area with [Formula: see text] water depth above a known gas province offshore Norway. The effect of the airwave is seen clearly in measured data. After field decomposition just below the seabed, the upgoing component of the recorded electric field has almost linear phase, indicating that most of the effect of the airwave component has been removed.

scholarly journals Joint inversion of EM and magnetic data for near‐surface studies

Geophysics ◽  
2002 ◽  
Vol 67 (6) ◽  
pp. 1729-1739 ◽  
Author(s):  
Christophe Benech ◽  
Alain Tabbagh ◽  
Guy Desvignes
Keyword(s):  
Magnetic Susceptibility ◽  
Case Studies ◽  
Joint Inversion ◽  
Synthetic Data ◽  
Magnetic Data ◽  
Near Surface ◽  
Data Inversion ◽  
Electromagnetic Measurements ◽  
Geophysical Surveys ◽  
Depth Analysis

Magnetic and electromagnetic measurements are influenced by magnetic susceptibility and, thus, are widely used in geophysical surveys for archeology or pedology. To date, the data inversion is performed separately. A filtering process incorporating both types of data is presented here. After testing the algorithm with synthetic data, the algorithm is used in several case studies in archeological prospecting. This approach presents two advantages: establishing the presence of remanent magnetizations (viscous or thermoremanent), and achieving more refined depth analysis of the anomaly.

Stripping induced polarization effects from airborne electromagnetics to improve 3D conductivity inversion of a narrow palaeovalley

Geophysics ◽  
2020 ◽  
Vol 85 (5) ◽  
pp. B161-B167 ◽  
Author(s):  
James Macnae ◽  
Xiuyan Ren ◽  
Tim Munday
Keyword(s):  
Thin Sheet ◽  
Physical Property ◽  
Original Data ◽  
Induced Polarization ◽  
Near Surface ◽  
Conductivity Distribution ◽  
Electromagnetic Data ◽  
Conductivity Structure ◽  
Airborne Electromagnetic ◽  
Airborne Electromagnetic Data

The electrical conductivity distribution within wide palaeochannels is usually well-mapped from airborne electromagnetic data using stitched 1D algorithms. Such stitched 1D solutions are, however, inappropriate for narrow valleys. An alternative option is to consider 2D or 3D models to allow for finite lateral extent of conductors. In airborne electromagnetic data within the Musgrave block near the well-studied Valen conductor, strong induced polarization (IP) and superparamagnetic (SPM) effects make physical property and structure estimation even more uncertain for deep channel clays, particularly those whose channel widths are comparable to their depth of burial. We developed a recursive data fitting algorithm based on dispersive thin sheet responses. The separate IP and SPM components of the fit provide near-surface chargeability and SPM distributions, and the associated electromagnetic (EM) fit provides stripped data with monotonic decays compatible with a simple nondispersive conductivity model. The validity of this stripped data prediction was tested through a comparison of 1D conductivity-depth imaging and 3D inversion applied to the original data and the stripped data. Due to the forked geometry of the deep conductivity structure in the region we investigated, we successfully used 3D rather than 2D inversion to predict the conductivity distribution related to the EM data. We recovered from the stripped data a continuous conductivity structure consistent with a branching, clay-filled palaeovalley under cover.

Regularization and datuming of seismic data by weighted, damped least squares

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. U67-U76 ◽  
Author(s):  
Robert J. Ferguson
Keyword(s):  
Least Squares ◽  
Seismic Data ◽  
Synthetic Data ◽  
Real Data ◽  
Structural Data ◽  
Irregular Sampling ◽  
Data Set ◽  
Near Surface ◽  
Damped Least Squares ◽  
Wavefield Extrapolation

The possibility of improving regularization/datuming of seismic data is investigated by treating wavefield extrapolation as an inversion problem. Weighted, damped least squares is then used to produce the regularized/datumed wavefield. Regularization/datuming is extremely costly because of computing the Hessian, so an efficient approximation is introduced. Approximation is achieved by computing a limited number of diagonals in the operators involved. Real and synthetic data examples demonstrate the utility of this approach. For synthetic data, regularization/datuming is demonstrated for large extrapolation distances using a highly irregular recording array. Without approximation, regularization/datuming returns a regularized wavefield with reduced operator artifacts when compared to a nonregularizing method such as generalized phase shift plus interpolation (PSPI). Approximate regularization/datuming returns a regularized wavefield for approximately two orders of magnitude less in cost; but it is dip limited, though in a controllable way, compared to the full method. The Foothills structural data set, a freely available data set from the Rocky Mountains of Canada, demonstrates application to real data. The data have highly irregular sampling along the shot coordinate, and they suffer from significant near-surface effects. Approximate regularization/datuming returns common receiver data that are superior in appearance compared to conventional datuming.

Resistive limit modeling of airborne electromagnetic data

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 492-500 ◽  
Author(s):  
James E. Reid ◽  
James C. Macnae
Keyword(s):  
Current Flow ◽  
Integral Equation Method ◽  
Near Surface ◽  
Electromagnetic Data ◽  
Airborne Electromagnetic ◽  
Source Current ◽  
Numerical Model Experiments ◽  
Airborne Electromagnetic Data ◽  
Airborne Em ◽  
Direct Induction

When a confined conductive target embedded in a conductive host is energized by an electromagnetic (EM) source, current flow in the target comes from both direct induction of vortex currents and current channeling. At the resistive limit, a modified magnetometric resistivity integral equation method can be used to rapidly model the current channeling component of the response of a thin-plate target energized by an airborne EM transmitter. For towed-bird transmitter–receiver geometries, the airborne EM anomalies of near-surface, weakly conductive features of large strike extent may be almost entirely attributable to current channeling. However, many targets in contact with a conductive host respond both inductively and galvanically to an airborne EM system. In such cases, the total resistive-limit response of the target is complicated and is not the superposition of the purely inductive and purely galvanic resistive-limit profiles. Numerical model experiments demonstrate that while current channeling increases the width of the resistive-limit airborne EM anomaly of a wide horizontal plate target, it does not necessarily increase the peak anomaly amplitude.

3D Modeling for Environmental Informatics

2015 ◽  
pp. 199-218
Author(s):  
Xiaozheng Zhang ◽  
Yongsheng Gao
Keyword(s):  
3D Modeling ◽  
Image Representation ◽  
Synthetic Data ◽  
3D Models ◽  
3D Object ◽  
Convex Object ◽  
Dimensional Linear Subspace ◽  
Environmental Informatics ◽  
Pixel Image ◽  
Tool Set

3D modeling plays an important role in the field of computer vision and image processing. It provides a convenient tool set for many environmental informatics tasks, such as taxonomy and species identification. This chapter discusses a novel way of building the 3D models of objects from their varying 2D views. The appearance of a 3D object depends on both the viewing directions and illumination conditions. What is the set of images of an object under all viewing directions? In this chapter, a novel image representation is proposed, which transforms any n-pixel image of a 3D object to a vector in a 2n-dimensional pose space. In such a pose space, it is proven that the transformed images of a 3D object under all viewing directions form a parametric manifold in a 6-dimensional linear subspace. With in-depth rotations along a single axis in particular, this manifold is an ellipse. Furthermore, it is shown that this parametric pose manifold of a convex object can be estimated from a few images in different poses and used to predict object's appearances under unseen viewing directions. These results immediately suggest a number of approaches to object recognition, scene detection, and 3D modeling, applicable to environmental informatics. Experiments on both synthetic data and real images were reported, which demonstrates the validity of the proposed representation.

Near-surface scattering phenomena and implications for tunnel detection

2015 ◽  
Vol 3 (1) ◽  
pp. SF43-SF54 ◽  
Author(s):  
Shelby L. Peterie ◽  
Richard D. Miller
Keyword(s):  
Synthetic Data ◽  
P Wave ◽  
S Wave ◽  
Seismic Line ◽  
Data Set ◽  
Near Surface ◽  
Tunnel Detection ◽  
Impedance Contrast ◽  
Diffraction Imaging ◽  
Imaging Algorithms

Tunnel locations are accurately interpreted from diffraction sections of focused mode converted P- to S-wave diffractions from a perpendicular tunnel and P-wave diffractions from a nonperpendicular (oblique) tunnel. Near-surface tunnels are ideal candidates for diffraction imaging due to their small size relative to the seismic wavelength and large acoustic impedance contrast at the tunnel interface. Diffraction imaging algorithms generally assume that the velocities of the primary wave and the diffracted wave are approximately equal, and that the diffraction apex is recorded directly above the scatterpoint. Scattering phenomena from shallow tunnels with kinematic properties that violate these assumptions were observed in one field data set and one synthetic data set. We developed the traveltime equations for mode-converted and oblique diffractions and demonstrated a diffraction imaging algorithm designed for the roll-along style of acquisition. Potential processing and interpretation pitfalls specific to these diffraction types were identified. Based on our observations, recommendations were made to recognize and image mode-converted and oblique diffractions and accurately interpret tunnel depth, horizontal location, and azimuth with respect to the seismic line.

Custom Patient-Specific Three-Dimensional Printed Mitral Valve Models for Pre-Operative Patient Education Enhance Patient Satisfaction and Understanding

2019 ◽  
Vol 13 (3) ◽  
Author(s):  
Kay S. Hung ◽  
Michael J. Paulsen ◽  
Hanjay Wang ◽  
Camille Hironaka ◽  
Y. Joseph Woo
Keyword(s):  
Patient Education ◽  
Mitral Valve ◽  
Three Dimensional ◽  
3D Models ◽  
Patient Specific ◽  
Imaging Data ◽  
Anatomical Models ◽  
Mitral Valves ◽  
Flexible Polymer ◽  
3D Printed

In recent years, advances in medical imaging and three-dimensional (3D) additive manufacturing techniques have increased the use of 3D-printed anatomical models for surgical planning, device design and testing, customization of prostheses, and medical education. Using 3D-printing technology, we generated patient-specific models of mitral valves from their pre-operative cardiac imaging data and utilized these custom models to educate patients about their anatomy, disease, and treatment. Clinical 3D transthoracic and transesophageal echocardiography images were acquired from patients referred for mitral valve repair surgery and segmented using 3D modeling software. Patient-specific mitral valves were 3D-printed using a flexible polymer material to mimic the precise geometry and tissue texture of the relevant anatomy. 3D models were presented to patients at their pre-operative clinic visit and patient education was performed using either the 3D model or the standard anatomic illustrations. Afterward, patients completed questionnaires assessing knowledge and satisfaction. Responses were calculated based on a 1–5 Likert scale and analyzed using a nonparametric Mann–Whitney test. Twelve patients were presented with a patient-specific 3D-printed mitral valve model in addition to standard education materials and twelve patients were presented with only standard educational materials. The mean survey scores were 64.2 (±1.7) and 60.1 (±5.9), respectively (p = 0.008). The use of patient-specific anatomical models positively impacts patient education and satisfaction, and is a feasible method to open new opportunities in precision medicine.

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