What is the depth of investigation of a resistivity measurement?

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. W1-W10 ◽  
Author(s):  
Enrique Gómez-Treviño ◽  
Francisco J. Esparza
Keyword(s):  
Apparent Resistivity ◽  
Resistivity Measurement ◽  
Weighted Average ◽  
Sensitivity Function ◽  
Resistivity Sounding ◽  
Practical Applications ◽  
Resistivity Profile ◽  
Definition Of ◽  
Homogeneous Media ◽  
Depth Of Investigation

Ever since the first computation of resistivity sounding curves, there has been the impression that somehow they are averages of the vertical resistivity profile. This prompted the idea to represent apparent resistivity as an integral over depth and to define depth of investigation using the integrands of the integrals as elementary contributions. However, elementary contributions for a boundary value problem cannot be uniquely defined and are not physically meaningful. Many practical applications that have been derived from this approach might be at stake regarding their theoretical basis. On the other hand, a sensitivity function has a definite physical meaning and it is uniquely defined, but it offers a different picture for a layered earth. The concept of elementary contributions must then be abandoned as not real, as some respected scholars have suggested, or it must be put on solid ground if we are going to continue using it. Our claim is that any definition of elementary contributions must comply with the concept of sensitivity; otherwise, it must be discarded not because it might be proved wrong, but because we cannot have multiple functions pretending to represent the depth of investigation of a resistivity measurement. We determined that both concepts can be unified and reconciled into a single formulation. That is, one and the same function of depth can be interpreted as an elementary contribution or as the local sensitivity. To further support the effectiveness of the concept, we applied it beyond its traditional application to homogeneous media. We developed an approximate formula for computing apparent resistivity as a weighted average of the vertical resistivity profile. The formula works in the way of a toy model; it is an approximation, but it provides immediate insights into how a vertical resistivity profile relates to its sounding curve.

A NEW METHOD FOR DIFFERENTIAL RESISTIVITY SOUNDING

Geophysics ◽  
1969 ◽  
Vol 34 (6) ◽  
pp. 924-943 ◽  
Author(s):  
Adel A. R. Zohdy
Keyword(s):  
Apparent Resistivity ◽  
New Method ◽  
Resolving Power ◽  
Symmetric System ◽  
Electrode Spacing ◽  
Electrode Arrays ◽  
Resistivity Sounding ◽  
Probing Depth ◽  
Earth Models ◽  
Homogeneous Media

A new method designated TDS (transverse differential sounding) is proposed for obtaining high resolution direct current resistivity soundings in the field. The measured apparent resistivity is designated TDR (transverse differential resistivity) and is defined by [Formula: see text], where [Formula: see text] and L are the Schlumberger apparent resistivity and electrode spacing, respectively. A collinear symmetric system (B′AMNBA′) consisting of two pairs of current electrodes and one pair of potential electrodes is used for measuring the value of [Formula: see text] directly in the field. For the interpretation of TDS curves obtained in the field, theoretical sets of master curves are computed either directly from the formal expression for [Formula: see text] in terms of Stefanesco’s kernel function and Bessel functions or by transformation of Schlumberger (VES) and/or dipole‐dipole sounding curves. Conversely, TDS and VES curves computed for the same horizontally stratified earth models and for corresponding electrode spacings are easily transformed, by means of simple relations, into radial, perpendicular, and parallel dipole‐dipole, or LDS (longitudinal differential sounding) curves. It is mathematically established that TDS curves, for horizontally stratified laterally homogeneous media, are identical to sounding curves obtained with a parallel dipole‐dipole array at an azimuth angle of 60 degrees, and that negative values of apparent resistivity [Formula: see text] are measured for certain geoelectric sections. Examples of theoretical TDS and LDS curves for two‐, three‐, and four‐layer earth models compared with corresponding VES curves illustrate the higher resolving power and greater probing depth of differential soundings. The field procedures and electric current requirements described for TDS and other types of soundings show that seven apparent resistivity values, corresponding to four electrode arrays, can be measured at each electrode setup.

Resolution and measurement in the scanning electron microscope

1987 ◽  
Vol 45 ◽  
pp. 534-537 ◽  
Author(s):  
Michael T. Postek
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Engineering Design ◽  
Resolving Power ◽  
Practical Applications ◽  
Instrument Resolution ◽  
Accurate Definition ◽  
Definition Of ◽  
Scanning Electron ◽  
Better Than

The term ultimate resolution or resolving power is the very best performance that can be obtained from a scanning electron microscope (SEM) given the optimum instrumental conditions and sample. However, as it relates to SEM users, the conventional definitions of this figure are ambiguous. The numbers quoted for the resolution of an instrument are not only theoretically derived, but are also verified through the direct measurement of images on micrographs. However, the samples commonly used for this purpose are specifically optimized for the measurement of instrument resolution and are most often not typical of the sample used in practical applications.SEM RESOLUTION. Some instruments resolve better than others either due to engineering design or other reasons. There is no definitively accurate definition of how to quantify instrument resolution and its measurement in the SEM.

Magnetotelluric static shift: Estimation and removal using the cokriging method

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. F25-F34 ◽  
Author(s):  
Benoit Tournerie ◽  
Michel Chouteau ◽  
Denis Marcotte
Keyword(s):  
Apparent Resistivity ◽  
A Priori ◽  
Shift Factor ◽  
Static Shift ◽  
Geostatistical Model ◽  
Data Set ◽  
Resistivity Sounding ◽  
The Difference ◽  
Cross Variogram

We present and test a new method to correct for the static shift affecting magnetotelluric (MT) apparent resistivity sounding curves. We use geostatistical analysis of apparent resistivity and phase data for selected periods. For each period, we first estimate and model the experimental variograms and cross variogram between phase and apparent resistivity. We then use the geostatistical model to estimate, by cokriging, the corrected apparent resistivities using the measured phases and apparent resistivities. The static shift factor is obtained as the difference between the logarithm of the corrected and measured apparent resistivities. We retain as final static shift estimates the ones for the period displaying the best correlation with the estimates at all periods. We present a 3D synthetic case study showing that the static shift is retrieved quite precisely when the static shift factors are uniformly distributed around zero. If the static shift distribution has a nonzero mean, we obtained best results when an apparent resistivity data subset can be identified a priori as unaffected by static shift and cokriging is done using only this subset. The method has been successfully tested on the synthetic COPROD-2S2 2D MT data set and on a 3D-survey data set from Las Cañadas Caldera (Tenerife, Canary Islands) severely affected by static shift.

scholarly journals Packaged Droplet Microresonator for Thermal Sensing with High Sensitivity

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3881 ◽  
Author(s):  
Xiaogang Chen ◽  
Liang Fu ◽  
Qijing Lu ◽  
Xiang Wu ◽  
Shusen Xie
Keyword(s):  
Liquid Droplet ◽  
Thermal Sensitivity ◽  
High Sensitivity ◽  
Liquid Limit ◽  
Practical Applications ◽  
Sensing Applications ◽  
Cavity Structure ◽  
Thermal Sensing ◽  
Facile Fabrication ◽  
Definition Of

Liquid droplet and quasi-droplet whispering gallery mode (WGM) microcavities have been widely studied recently for the enhanced spatial overlap between the liquid and WGM field, especially in sensing applications. However, the fragile cavity structure and the evaporation of liquid limit its practical applications. Here, stable, packaged, quasi-droplet and droplet microcavities are proposed and fabricated for thermal sensing with high sensitivity. The sensitivity and electromagnetic field intensity distribution are analyzed by Mie theory, and a quantified definition of the quasi-droplet is presented for the first time to the best of our knowledge. By doping dye material directly into the liquid, lasing packaged droplet and quasi-droplet microcavity sensors with a high thermal sensitivity of up to 205.3 pm/°C are experimentally demonstrated. The high sensitivity, facile fabrication, and mechanically robust properties of the optofluidic, packaged droplet microresonator make it a promising candidate for future integrated photonic devices.

scholarly journals Numerical Modeling of the Effects of Electrode Spacing and Multilayered Concrete Resistivity on the Apparent Resistivity Measured Using Wenner Method

2020 ◽  
Author(s):  
Karthick Thiyagarajan ◽  
Parikshit Acharya ◽  
Lasitha Piyathilaka ◽  
sarath kodagoda
Keyword(s):  
Contact Area ◽  
Apparent Resistivity ◽  
Resistivity Measurement ◽  
Gaussian Process Regression ◽  
Electrode Spacing ◽  
Electrical Resistivity Measurement ◽  
Resistivity Measurements ◽  
Electrode Contact ◽  
Concrete Resistivity ◽  
Moisture Conditions

Smart Sensing technologies can play an important role in the conditional assessment of concrete sewer pipe linings. In the long-term, the permeation of acids can deteriorate the pipe linings. Currently, there are no proven sensors available to non-invasively estimate the depth of acid permeation in real-time. The electrical resistivity measurement on the surface of the linings can indicate the sub-surface acid moisture conditions. In this study, we consider acid permeated linings as a two resistivity layer concrete sample, where the top resistivity layer is assumed to be acid permeated and the bottom resistivity layer indicates normal moisture conditions. Firstly, we modeled the sensor based on the four-probe Wenner method. The measurements of the developed model were compared with the previous studies for validation. Then, the sensor model was utilized to study the effects of electrode contact area, electrode spacing distance and two resistivity layered concrete on the apparent resistivity measurements. All the simulations were carried out by varying the thickness of top resistivity layer concrete. The simulation study indicated that the electrode contact area has very minimal effects on apparent resistivity measurements. Also, an increase in apparent resistivity measurements was observed when there is an increase in the distance of the electrode spacing. Further, a machine learning approach using Gaussian process regression modeling was formulated to estimate the depth of acid permeated layer

scholarly journals The dynamics of Pecking Order and Agency theories on crowdfunding concept as alternate finance for start-up businesses

2020 ◽  
Vol 5 (1) ◽  
pp. 1-13
Author(s):  
Francis Kwaku Kuma ◽  
Mohd Effandi Yosuff
Keyword(s):  
Theoretical Aspect ◽  
Review Of Literature ◽  
Pecking Order ◽  
Practical Applications ◽  
Theoretical Perspectives ◽  
Start Up ◽  
Key Concepts ◽  
Definition Of ◽  
The Relationship

The study explores the relevance of theoretical aspect of crowd financing by reviewing the defining literature on Pecking Order and Agency theories in details and evaluates applications of these theories based on crowdfunding. In particular, the study critically considers the key concepts of these theories and how they could be applied in practical terms. The study decides to adopt Pecking Order and the Agency theories because they provide valuable insights into the trend of crowdfunding streams available to firms. The paper primarily adds to existing literature on the broader definition of crowdfunding as a concept and then examine the relationship between this concept and its practical applications to the chosen theories. The study combines these theoretical perspectives with the practical aspects of startup companies raising finance using the crowd because a broad reading of the literature tends to point to in this direction. The key concepts of these theories are critically considered and the study is conducted in the form of review of literature and expression of opinion. Citation: author1, author2, author3. The dynamics of Pecking Order and Agency theories on crowdfunding concept as alternate finance for start-up businesses. 2020; 4(1): 1－13.Received: (February 2, 2020) Accepted: (March 31, 2020)

Social Computing

2018 ◽  
pp. 7796-7804
Author(s):  
Nolan Hemmatazad
Keyword(s):  
Large Scale ◽  
Social Computing ◽  
Social Needs ◽  
Content Creation ◽  
Broad Definition ◽  
Practical Applications ◽  
Research Themes ◽  
The Social ◽  
Definition Of ◽  
Near Future

Broadly speaking, social computing encapsulates the idea of making technologies more aware of, and more in alignment with, the social needs of their users. This allows for the introduction of new modes of communication and collaboration among users, the ability to establish and grow communities of various constitutions, as well as for more dynamic and large scale content creation, dissemination, and evaluation. This chapter serves the ternary purpose of establishing a broad definition of social computing as it stands today and as it is expected to evolve in the near future, providing an overview of the practical applications of social computing, and examining the present and historic research themes that have made an impression on social computing as an area of academic intrigue. The chapter is intended to be accessible to casual readers, practitioners, and academicians alike, with little technical depth and broad focus throughout, for the purpose of establishing an initial acquaintance with the field.

Social Computing

2019 ◽  
pp. 1200-1210
Author(s):  
Nolan Hemmatazad
Keyword(s):  
Large Scale ◽  
Social Computing ◽  
Social Needs ◽  
Content Creation ◽  
Broad Definition ◽  
Practical Applications ◽  
Research Themes ◽  
The Social ◽  
Definition Of ◽  
Near Future

Broadly speaking, social computing encapsulates the idea of making technologies more aware of, and more in alignment with, the social needs of their users. This allows for the introduction of new modes of communication and collaboration among users, the ability to establish and grow communities of various constitutions, as well as for more dynamic and large-scale content creation, dissemination, and evaluation. This chapter serves the ternary purpose of establishing a broad definition of social computing as it stands today and as it is expected to evolve in the near future, providing an overview of the practical applications of social computing, and examining the present and historic research themes that have made an impression on social computing as an area of academic intrigue. The chapter is intended to be accessible to casual readers, practitioners, and academicians alike, with little technical depth and broad focus throughout, for the purpose of establishing an initial acquaintance with the field.

scholarly journals Breaks in Resistivity Sounding Curves as Indicators of Hard Rock Aquifers

1983 ◽  
Vol 14 (1) ◽  
pp. 33-40 ◽  
Author(s):  
P. N. Ballukraya ◽  
R. Sakthivadivel ◽  
R. Baratan
Keyword(s):  
Empirical Study ◽  
Deep Water ◽  
Apparent Resistivity ◽  
Hard Rock ◽  
Fracture Zones ◽  
Resistivity Sounding ◽  
Resistivity Method ◽  
Hard Rock Aquifers

In a previous paper (Nordic Hydrology, Vol. 12, 1981), the authors have discussed the inadequacies in the technique of resistivity method for location of sites for constructing deep water walls in hard rock areas. It was pointed out that the water bearing fracture zones in the bed rock could not be identified by merely considering geoelectrical parameters such as layer resistivity. An empirical study based on the correlation of minor irregularities or deviations – “BREAKS” – in the normally smooth sounding curves with the actual driller's logs reveals that under normal geo-electric conditions these water bearing zones (hard rock aquifers) are indicated in the curve by a perceptible lowering of apparent resistivity and hence could be used as a guide for locating well sites. As such breaks may also be caused by other conditions such as lateral inhomogeneities, certain methods for distinguishing them are discussed.

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