Effective skin depth with a local source and its application to survey design and data interpretation

Doubling the effective skin depth with a local source

Geophysics ◽

10.1190/1.1444582 ◽

1999 ◽

Vol 64 (3) ◽

pp. 732-738 ◽

Cited By ~ 13

Author(s):

James E. Reid ◽

James C. Macnae

Keyword(s):

Plane Wave ◽

Half Space ◽

Survey Design ◽

Data Interpretation ◽

Skin Depth ◽

Local Source ◽

Electromagnetic Sounding ◽

Homogeneous Half Space ◽

Electric And Magnetic Fields ◽

Thick Overburden

The depth at which the amplitude of the frequency‐domain electromagnetic fields due to dipole and square loop sources over a homogeneous half‐space fall to 1/e of their value at the surface is compared to the conventional plane‐wave skin depth. The skin depth due to a local source depends on the transmitter frequency, half‐space conductivity, transmitter altitude, and transmitter‐receiver offset, and may range from a fraction of to more than twice the plane‐wave skin depth. Unlike the plane‐wave skin depth, the “local‐source skin depth” is different for electric and magnetic fields, and may be nonunique for some transmitter geometries and field components. For all transmitter geometries, however, the local‐source skin depth approaches the plane‐wave skin depth as the transmitter altitude and/or receiver offset increase. The concept of the local‐source skin depth has direct application to survey design and data interpretation. A theoretical example demonstrates that it is possible to predict, for a given survey geometry and frequency range, whether or not an electromagnetic sounding can detect a conductive basement below a thick overburden layer.

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Depth of investigation for small broadband electromagnetic sensors

Geophysics ◽

10.1190/1.2122412 ◽

2005 ◽

Vol 70 (6) ◽

pp. G135-G142 ◽

Cited By ~ 57

Author(s):

Haoping Huang

Keyword(s):

Detection Threshold ◽

Data Interpretation ◽

Skin Depth ◽

High Threshold ◽

Electromagnetic Sensors ◽

Quantitative Understanding ◽

Processing Techniques ◽

Simple Equations ◽

Depth Of Investigation ◽

Conductivity Contrast

The depth of investigation in electromagnetic (EM) soundings is a maximum depth at which a given target in a given host can be detected by a given sensor. It is of primary interest in EM exploration, particularly for small EM sensors having negligible separation between the transmitter and receiver coils. The depth of investigation is related to many factors, such as sensor sensitivity, precision, operating frequencies, ambient noise level, target and host properties, and the techniques used in data processing and interpretation. Quantitative understanding of the relationships between the depth of investigation and these factors will help users meet their geologic objectives, avoid unnecessary survey expenses, and display meaningful geologic features. Simple equations to estimate the depth of investigation for handheld EM sensors have been derived from analyzing the EM response based on layered half-space models. The results show that the depth of investigation is approximately proportional to the square root of the skin depth in the host for a given detection threshold and conductivity contrast between the target and host. For a given skin depth, the depth of investigation increases with the target conductivity and conductivity contrast and decreases with the detection threshold. Choosing a threshold mainly depends on the S/N ratio of the EM data if the sensor setup, data acquisition methods, and processing techniques are well established. A high threshold such as 20% or 30% is recommended for resistive targets or in areas where environmental noise is high or where terrain conductivity is low (<50 mS/m). In contrast, a threshold as low as 5% or 10% can be used for conductive targets in quiet areas. Field examples are presented to illustrate how to use the depth of investigation in data interpretation and presentation.

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Seasonal and interannual variation in vegetation composition: Implications for survey design and data interpretation

Austral Ecology ◽

10.1111/aec.12141 ◽

2014 ◽

Vol 39 (7) ◽

pp. 755-766 ◽

Cited By ~ 9

Author(s):

Nick L. Schultz ◽

Nick Reid ◽

Greg Lodge ◽

John T. Hunter

Keyword(s):

Interannual Variation ◽

Survey Design ◽

Data Interpretation ◽

Vegetation Composition

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The Generalized Skin Depth for Polarized Porous Media Based on the Cole–Cole Model

Applied Sciences ◽

10.3390/app10041456 ◽

2020 ◽

Vol 10 (4) ◽

pp. 1456

Author(s):

Yanju Ji ◽

Xiangdong Meng ◽

Jingya Shao ◽

Yanqi Wu ◽

Qiong Wu

Keyword(s):

Porous Media ◽

Electromagnetic Wave ◽

Frequency Domain ◽

Low Frequency ◽

Theoretical Data ◽

Data Interpretation ◽

Induced Polarization ◽

Skin Depth ◽

Imaging Results ◽

Frequency Excitation

In the field of frequency-domain electromagnetic detection, skin depth is an important parameter for electromagnetic data interpretation and imaging. The classic skin depth formula is calculated based only on conductivity; the induced-polarization effect in real earth is not considered, so the imaging results have obvious errors. To solve these problems, based on plane wave theory and the Cole–Cole conductivity model, a generalized skin depth formula of polarized media is derived in the frequency domain. The accuracy of the generalized skin depth is verified through comparison with the classical skin depth. To show the practicability of this study, the theoretical data with induced polarization (IP) effects are used to explain the generalized skin depth for polarized porous media. The generalized skin depth calculation for a typical porous polarization model is related not only to conductivity, but also to polarization parameters, such as chargeability, characteristic time constant, and frequency dependence. At low-frequency excitation, the generalized skin depth formula can be used to calculate the propagation depth of electromagnetic waves relatively accurately for porous polarized media. This method can be applied to the calculation of electromagnetic wave propagation depths in complex dispersive media. Compared with non-polarized media, in porous polarized media, under low-frequency excitation, the electromagnetic wave propagates deeper, allowing the detection of deeper objects. The data interpretation and imaging of polarized porous media by the generalized skin depth formula have higher accuracy.

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A new formula to compute apparent resistivities from marine magnetometric resistivity data

Geophysics ◽

10.1190/1.2194513 ◽

2006 ◽

Vol 71 (3) ◽

pp. G73-G81

Author(s):

Jiuping Chen ◽

Douglas W. Oldenburg

Keyword(s):

Magnetic Field ◽

Apparent Resistivity ◽

Survey Design ◽

Radial Distance ◽

Data Interpretation ◽

Azimuthal Component ◽

Sea Floor ◽

Layered Earth ◽

New Formula ◽

The Magnetic Field

Magnetometric resistivity (MMR) is an electromagnetic (EM) exploration method that has been used successfully to investigate electrical-resistivity structures below the sea-floor. Apparent resistivity, derived from the observed azimuthal component of the magnetic field, often is used as an approximation to the resistivity of a layered earth. Two commonly used formulas to compute the apparent resistivity have their own limitations and are invalid for a deep-sea experiment. In this paper, we derive an apparent-resistivity formula based upon the magnetic field resulting from a semi-infinite electrode buried in a 1D layered earth. This new formula can be applied to both shallow and deep marine MMR surveys. In addition, we address the effects that arise from the transmitter-receiver (Tx-Rx) depth difference and the choice of the normalized range (the radial distance between transmitter and receiver, divided by the thickness of seawater) on data interpretation and survey design. The performance of the new formula is shown by processing synthetic and field data.

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Converted‐wave seismic exploration: Methods

Geophysics ◽

10.1190/1.1512781 ◽

2002 ◽

Vol 67 (5) ◽

pp. 1348-1363 ◽

Cited By ~ 112

Author(s):

Robert R. Stewart ◽

James E. Gaiser ◽

R. James Brown ◽

Don C. Lawton

Keyword(s):

Survey Design ◽

Data Interpretation ◽

P Wave ◽

Seismic Exploration ◽

Single Element ◽

S Wave ◽

Converted Wave ◽

P Waves ◽

Prestack Migration ◽

Recording Channels

Multicomponent seismic recording (measurement with vertical‐ and horizontal‐component geophones and possibly a hydrophone or microphone) captures the seismic wavefield more completely than conventional single‐element techniques. In the last several years, multicomponent surveying has developed rapidly, allowing creation of converted‐wave or P‐S images. These make use of downgoing P‐waves that convert on reflection at their deepest point of penetration to upcoming S‐waves. Survey design for acquiring P‐S data is similar to that for P‐waves, but must take into account subsurface VP/VS values and the asymmetric P‐S ray path. P‐S surveys use conventional sources, but require several times more recording channels per receiving location. Some special processes for P‐S analysis include anisotropic rotations, S‐wave receiver statics, asymmetric and anisotropic binning, nonhyperbolic velocity analysis and NMO correction, P‐S to P‐P time transformation, P‐S dip moveout, prestack migration with two velocities and wavefields, and stacking velocity and reflectivity inversion for S‐wave velocities. Current P‐S sections are approaching (and in some cases exceeding) the quality of conventional P‐P seismic data. Interpretation of P‐S sections uses full elastic ray tracing, synthetic seismograms, correlation with P‐wave sections, and depth migration. Development of the P‐S method has taken about 20 years, but has now become commercially viable.

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High Resolution Microscopy of Multi-Layered Biological Crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010005319x ◽

1982 ◽

Vol 40 ◽

pp. 80-83

Author(s):

H.A. Cohen ◽

T.W. Jeng ◽

W. Chiu

Keyword(s):

High Resolution ◽

Low Dose ◽

Three Dimensional ◽

Data Interpretation ◽

Two Dimensional ◽

Biological Objects ◽

Density Maps ◽

Density Map ◽

Complex Crystal ◽

High Resolution Microscopy

This tutorial will discuss the methodology of low dose electron diffraction and imaging of crystalline biological objects, the problems of data interpretation for two-dimensional projected density maps of glucose embedded protein crystals, the factors to be considered in combining tilt data from three-dimensional crystals, and finally, the prospects of achieving a high resolution three-dimensional density map of a biological crystal. This methodology will be illustrated using two proteins under investigation in our laboratory, the T4 DNA helix destabilizing protein gp32*I and the crotoxin complex crystal.

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Alleviation of pain and depression by specific neural transplants: Fine structural correlates

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100129966 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1066-1067

Author(s):

George D. Pappas ◽

Jacqueline Sagen

Keyword(s):

Opioid Peptides ◽

Chromaffin Cells ◽

Pain Sensitivity ◽

Opioid Peptide ◽

Local Source ◽

Pain Models ◽

Neural Transplants ◽

Adrenergic Antagonists ◽

Csf Levels ◽

Donor Source

We have been interested in the use of neural transplants mainly as a local source of neuroactive substances, rather than as a replacement for damaged neural circuities. In particular, we have been exploring the possibilities of reducing pain by transplants of opioid peptide producing cells, and reducing depression by transplants of monoamine-producing cells. For the past several years, work in our laboratory has demonstrated in both acute and chronic pain models that transplantation of adrenal medullary tissue or isolated chromaffin cells into CNS pain modulatory regions can reduce pain sensitivity in rodents. Chromaffin cells were chosen as donor source since they produce high levels of both opioid peptides and catecholamines, substances which independently, and probably synergistically, reduce pain sensitivity when injected locally into the spinal cord. The analgesia produced by these transplants most likely results from the release of both opioid peptides and catecholamines, since it can be blocked or attenuated by opiate or adrenergic antagonists, respectively. Furthermore, CSF levels of met-enkephalin and catecholamines are increased by the transplants.

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