Differential Target Antenna Coupling (DTAC) EM Surveying with Stationary Transmitter Loop and Moving In-Loop Receivers

2020 ◽  
Vol 25 (1) ◽  
pp. 111-127
Author(s):  
Ben K. Sternberg
Keyword(s):  
False Alarm ◽  
Frequency Domain ◽  
Ground Surface ◽  
Primary Field ◽  
Vertical Arrays ◽  
Antenna Coupling ◽  
Operational Tests ◽  
Airborne Vehicle

Following our previous studies of the Differential Target Antenna Coupling (DTAC) method with horizontal and vertical arrays for EM surveys, in this paper we study the application of the DTAC method to a different configuration, where a large, stationary transmitter loop is on the ground surface. We then run profile lines inside this loop. The DTAC method is effective in eliminating errors due to the large variations in the primary field along profile lines within the transmitting loop. Operational tests show that we obtain more diagnostic DTAC anomalies over buried targets than using just the B x and B y data. The DTAC method also produces smaller false-alarm targets due to background geology variations, compared with B z measurements. The DTAC method can be used with either time- or frequency-domain data and the receiver can be moved on the ground or deployed from an airborne vehicle, such as a drone.

Airborne resistivity data leveling

Geophysics ◽  
1999 ◽  
Vol 64 (2) ◽  
pp. 378-385 ◽  
Author(s):  
Haoping Huang ◽  
Douglas C. Fraser
Keyword(s):  
Frequency Domain ◽  
Mineral Exploration ◽  
Primary Field ◽  
Geologic Mapping ◽  
Resistivity Data ◽  
High Magnitude ◽  
Geological Features ◽  
Absolute Measure ◽  
Tie Lines ◽  
Automated Technique

Helicopter‐borne frequency‐domain electromagnetic (EM) data are used routinely to produce resistivity maps for geologic mapping, mineral exploration, and environmental investigations. The integrity of the resistivity data depends in large part on the leveling procedures. Poor resistivity leveling procedures may, in fact, generate false features as well as eliminate real ones. Resistivity leveling is performed on gridded data obtained by transformation of the leveled EM channel data. The leveling of EM channel data is often imperfect, which is why the resistivity grids need to be leveled. We present techniques for removing the various types of resistivity leveling errors which may exist. A semi‐automated leveling technique uses pseudo tie‐lines to remove the broad flight‐based leveling errors and any high‐magnitude line‐based errors. An automated leveling technique employs a combination of 1-D and 2-D nonlinear filters to reject the rest of the leveling errors including both long‐and short‐wavelength leveling errors. These methods have proven to be useful for DIGHEM helicopter EM survey data. However, caution needs to be exercised when using the automated technique because it cannot distinguish between geological features parallel to the flight lines and leveling errors of the same wavelength. Resistivity leveling is not totally objective since there are no absolutes to the measured frequency‐domain EM data. The fundamental integrity of the EM data depends on calibration and the estimate of the EM zero levels. Zero level errors can be troublesome because there is no means by which the primary field can be determined absolutely and therefore subtracted to yield an absolute measure of the earth’s response. The transform of incorrectly zero‐leveled EM channels will yield resistivity leveling errors. Although resistivity grids can be leveled empirically to provide an esthetically pleasing map, this is insufficient because the leveling must also be consistent across all frequencies to allow resistivity to be portrayed in section. Generally, when the resistivity looks correct in plan and section, it is assumed to be correct.

A Spectral Approach to the Analysis of Rough Surfaces

1989 ◽  
Vol 111 (2) ◽  
pp. 359-363 ◽  
Author(s):  
H. Moalic ◽  
J. A. Fitzpatrick ◽  
A. A. Torrance
Keyword(s):  
Finite Difference ◽  
Frequency Domain ◽  
Rough Surfaces ◽  
Finite Difference Methods ◽  
Ground Surface ◽  
Spectral Approach ◽  
Digital Differentiator ◽  
Sample Spacing ◽  
Probe Size ◽  
Difference Methods

A brief summary of the methods commonly used for the analysis of rough surfaces and the errors associated with these techniques is given. A frequency domain digital differentiator is shown to reduce the bias errors for estimates of the properties of slopes and curvatures for a sample spacing determined by the profilometer probe size. A comparison of this “spectral” approach with finite difference methods for calculating slope and curvature characteristics for a ground surface show substantial underestimates for the latter methods.

CONVERSION OF WIDEBAND EM FREQUENCY RESPONSE TO TRANSIENT RESPONSE USING SEGMENTED TRANSFORMATION

Geophysics ◽  
1978 ◽  
Vol 43 (1) ◽  
pp. 189-193 ◽  
Author(s):  
M. W. Asten ◽  
S. K. Verma
Keyword(s):  
Frequency Domain ◽  
Continuous Wave ◽  
Primary Field ◽  
Analog Model ◽  
Response Curves ◽  
Input System ◽  
Transient Nature ◽  
Field Response ◽  
Different Types ◽  
Linear Ramp

Electromagnetic (EM) methods measure the distortions of a primary field which are caused by a sub‐surface conductor. The resultant field is recorded as a function of frequency or of time, depending upon the harmonic or transient nature of the primary field. The two different types of measurements thus recognized are frequency domain (or continuous‐wave) and time domain (transient or TEM) methods. Interpretation of EM data is possible by comparing field response with the analytic or experimental response of a heuristic model. Most of the interpretive developments have been done for the frequency domain technique, which is mathematically more tractable than the TEM technique when we consider generalized models possessing a conductive halo, over‐burden, or host rock. For such models, TEM response is more easily obtained from analog model experiments (e.g., Velekin and Bulgakov, 1967; Palacky, 1975). Response curves thus obtained, however, are dependent upon the shape of the excitation pulse which varies among the different transient EM systems available; e.g., the Input system (Barringer, 1962) uses a 1.1 msec half‐sine pulse, the Crone pulse EM system (Crone, 1975) uses a linear ramp pulse with 1.4 msec rise time, while the Russian MPP01 system (Velekin and Bulgakov, 1967) uses a 15 msec square step pulse.

Automatic microseismic event detection using constant false alarm rate processing in time-frequency domain

2018 ◽  
Author(s):  
Anupama Govinda Raj ◽  
James H. McClellan ◽  
Naveed Iqbal ◽  
Abdullatif A. Al-Shuhail ◽  
SanLinn I. Kaka
Keyword(s):  
False Alarm ◽  
Frequency Domain ◽  
False Alarm Rate ◽  
Event Detection ◽  
Constant False Alarm Rate ◽  
Time Frequency ◽  
Microseismic Event

California Ground Motion Vertical Array Database

2019 ◽  
Vol 35 (4) ◽  
pp. 2003-2015 ◽  
Author(s):  
Kioumars Afshari ◽  
Jonathan P. Stewart ◽  
Jamison H. Steidl
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Ground Surface ◽  
Data Repository ◽  
Vertical Array ◽  
Data Set ◽  
Ground Shaking ◽  
Vertical Arrays ◽  
Direct Observations ◽  
Downhole Sensors

We present a data set of ground motion recordings and site information from vertical array sites in California. The recordings include two horizontal components of ground shaking at the ground surface level and from downhole sensors. The availability of both surface and downhole recordings at the same site facilitates direct observations of site response. The site data include measured shear-and compression-wave velocities, and, where available, geotechnical boring logs. We considered 39 vertical array sites in California and chose 21 for inclusion in the database on the basis of having at least four pairs of surface/downhole recordings. The recordings and site data are presented in a data repository, which is accessible at the DesignSafe platform (DOI: 10.17603/146DS2N680). The original digital accelerograms are processed in a manner consistent with NGA-West2 protocols. In this paper, this data set is compared to a similar but larger data set from Japanese vertical arrays compiled by others.

Numerical Simulation of Subway-Induced Environment Vibration

2013 ◽  
Vol 405-408 ◽  
pp. 1264-1267
Author(s):  
Pei Zhen Li ◽  
Zhao Hui Pan ◽  
Xiu Qiang Li ◽  
Jian Yong Yue
Keyword(s):  
Numerical Simulation ◽  
Frequency Domain ◽  
Ground Surface ◽  
Vertical Displacement ◽  
Displacement Amplitude ◽  
Loading Frequency ◽  
Soil Layers ◽  
Tunnel Model ◽  
Element Boundary ◽  
Abaqus Software

The ABAQUS software was used to establish an actual soil layers-tunnel model in which the infinite element boundary was adopted. Then, frequency domain analyses were conducted on the model under vertical train loads with different frequencies. The attenuation of the vertical displacement amplitude on ground surface under each load was computed in the area ranging from 0m to 30m. The results show that the displacement amplitude may rebound in a particular area under some loading frequencies and this phenomenon is closely related with the loading frequency.

A finite element multifrontal method for 3D CSEM modeling in the frequency domain

Geophysics ◽  
2012 ◽  
Vol 77 (2) ◽  
pp. E101-E115 ◽  
Author(s):  
Nuno Vieira da Silva ◽  
Joanna V. Morgan ◽  
Lucy MacGregor ◽  
Mike Warner
Keyword(s):  
Finite Element ◽  
Electric Field ◽  
Frequency Domain ◽  
Closed Form Solution ◽  
Form Solution ◽  
Computational Domain ◽  
Order Partial Differential Equation ◽  
Primary Field ◽  
Direct Solver ◽  
Linear System Of Equations

There has been a recent increase in the use of controlled-source electromagnetic (CSEM) surveys in the exploration for oil and gas. We developed a modeling scheme for 3D CSEM modeling in the frequency domain. The electric field was decomposed in primary and secondary components to eliminate the singularity originated by the source term. The primary field was calculated using a closed form solution, and the secondary field was computed discretizing a second-order partial differential equation for the electric field with the edge finite element. The solution to the linear system of equations was obtained using a massive parallel multifrontal solver, because such solvers are robust for indefinite and ill-conditioned linear systems. Recent trends in parallel computing were investigated for their use in mitigating the computational overburden associated with the use of a direct solver, and of its feasibility for 3D CSEM forward modeling with the edge finite element. The computation of the primary field was parallelized, over the computational domain and the number of sources, using a hybrid model of parallelism. When using a direct solver, the attainment of multisource solutions was only competitive if the same factors are used to achieve a solution for multi right-hand sides. This aspect was also investigated using the presented methodology. We tested our proposed approach using 1D and 3D synthetic models, and they demonstrated that it is robust and suitable for 3D CSEM modeling using a distributed memory system. The codes could thus be used to help design new surveys, as well to estimate subsurface conductivities through the implementation of an appropriate inversion scheme.

Hit and False-Alarm Rates of Selected ABR Indices in Differentiating Cochlear Disorders From Acoustic Tumors

1996 ◽  
Vol 5 (1) ◽  
pp. 90-96 ◽  
Author(s):  
Frank E. Musiek ◽  
Cynthia A. McCormick ◽  
Raymond M. Hurley
Keyword(s):  
False Alarm ◽  
Amplitude Ratio ◽  
High Specificity ◽  
Auditory Brainstem ◽  
Latency Difference ◽  
Cochlear Pathology ◽  
Brainstem Response ◽  
Absolute Latency ◽  
Two Indices ◽  
Low Sensitivity

We performed a retrospective study of 26 patients with acoustic tumors and 26 patients with otologically diagnosed cochlear pathology to determine the sensitivity (hit rate), specificity (false-alarm rate), and efficiency of six auditory brainstem response indices. In addition, a utility value was determined for each of these six indices. The I–V interwave interval, the interaural latency difference, and the absolute latency of wave V provided the highest hit rates, the best A’ values and good utility. The V/I amplitude ratio index provided high specificity but low sensitivity scores. In regard to sensitivity and specificity, using the combination of two indices provided little overall improvement over the best one-index measures.

Correction to "The analysis of slug tests in the frequency domain" (WRR 25(11), pp. 2388-2396

1990 ◽  
Vol 26 (8) ◽  
pp. 1863-1863
Author(s):  
Paul Marschall ◽  
Baldur Barczewski
Keyword(s):  
Frequency Domain ◽  
Slug Tests
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