Testing the limits of AEM bathymetry with a floating TEM system

Geophysics ◽  
2010 ◽  
Vol 75 (4) ◽  
pp. WA163-WA177 ◽  
Author(s):  
Julian Vrbancich ◽  
Peter Fullagar ◽  
Richard Smith
Keyword(s):  
Sediment Thickness ◽  
Data Set ◽  
Transient Electromagnetic ◽  
Empirical Correction ◽  
Airborne Electromagnetic ◽  
Low Levels ◽  
Low Altitude ◽  
Marine Seismic ◽  
Airborne Em ◽  
Base Data

A floating transient electromagnetic (TEM) system (“sea ring”) simulating a low-altitude helicopter airborne electromagnetic (AEM) system was constructed to test the accuracy of the AEM method for measuring water depth and estimating sediment thickness in shallow coastal waters. A square transmitter loop [Formula: see text], plus concentric inner and outer receiver loops, was strung from masts supported by the circular sea-ring base. Data were stacked over periods from 1 to approximately [Formula: see text] and with loop heights ranging between approximately 5.5 and [Formula: see text] above sea level. The towed sea ring provides a stable platform at a known fixed altitude in calm waters. We have undertaken modeling to investigate the effect of vertical and horizontal displacements of the loops, and to compare circular and square loopgeometries, in proximity to the sea surface. With relatively long stacking times, as long as approximately [Formula: see text], the uncertainty in altitude can be reduced to very low levels. The sea ring has been deployed near Port Lincoln, Australia, in an area with known bathymetry, seawater conductivity [Formula: see text], and sediment thickness (from marine seismic). Initial 1D inversion of raw sea-ring data highlighted significant instrument calibration errors. Empirical correction factors were defined to achieve agreement between measured and modeled TEM responses at selected control points. These corrections were then applied to the entire data set. The 1D inversion of corrected sea-ring data predicted seawater depths within approximately [Formula: see text] of known depths down to [Formula: see text]. These results provide an upper limit to the accuracy that can be expected from airborne EM systems for shallow bathymetry using current technology.

Airborne electromagnetic bathymetry and estimation of bedrock topography in Broken Bay, Australia

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. WB3-WB17 ◽  
Author(s):  
Julian Vrbancich
Keyword(s):  
Water Depth ◽  
Seismic Data ◽  
Sea Water ◽  
Unconsolidated Sediments ◽  
Sediment Thickness ◽  
Bedrock Topography ◽  
Transient Electromagnetic ◽  
Airborne Electromagnetic ◽  
Marine Seismic ◽  
Water Depths

A helicopter transient electromagnetic (TEM) survey was flown over shallow coastal waters in Broken Bay, Australia, overlying several palaeovalleys and exposed reef sections. The infilled palaeovalleys contain unconsolidated sediments with variable thicknesses exceeding 100 m. Previous marine seismic reflection and vibrocore studies provide an estimate of sediment thickness and surficial sediment conductivity, respectively, which, combined with known bathymetry (sonar soundings) and measured seawater conductivity, can be used to generate a crude 1D geoelectric ground-truth model consisting of two layers (seawater/sediment) overlying a relatively resistive basement. The primary focus was to examine the accuracy of interpreted water depths obtained by 1D inversion of airborne TEM data, assuming a two-layer over resistive basement model, by comparing these depths with known water depths. The secondary focus was to compare the interpreted sediment thickness (i.e., the thickness of the second geoelectric layer, which combined with bathymetry, gives the bedrock depth) with thicknesses estimated from marine seismic data to test the potential of using airborne electromagnetic systems for remote sensing of the coarse features of the bedrock topography. Interpreted water depths obtained from TEM data resulted in absolute water depth accuracies of 1–2 m for depths between 10 and 30 m, and 0.3–0.5 m in water shallower than [Formula: see text]. More importantly, similar water depth accuracies were obtained using raw TEM data (with birdswing removal) and TEM data obtained by postprocessing using time-consuming empirical corrections based on the TEM half-space response over deep sea water. The interpreted sediment depths derived from TEM and marine seismic data showed good agreement, generally, for example, inversion of TEM data delineated a distinct palaeovalley that transects a beach, with a maximum depth of 60–70 m below the seafloor, in agreement with depths estimated from marine seismic data to within [Formula: see text].

Simulated annealing for airborne EM inversion

Geophysics ◽  
2007 ◽  
Vol 72 (4) ◽  
pp. F189-F195 ◽  
Author(s):  
Changchun Yin ◽  
Greg Hodges
Keyword(s):  
Simulated Annealing ◽  
Random Walk ◽  
Boltzmann Distribution ◽  
Model Parameters ◽  
Local Minima ◽  
Model Configuration ◽  
Airborne Electromagnetic ◽  
Starting Model ◽  
Airborne Em ◽  
Cooling Schedule

The traditional algorithms for airborne electromagnetic (EM) inversion, e.g., the Marquardt-Levenberg method, generally run only a downhill search. Consequently, the model solutions are strongly dependent on the starting model and are easily trapped in local minima. Simulated annealing (SA) starts from the Boltzmann distribution and runs both downhill and uphill searches, rendering the searching process to easily jump out of local minima and converge to a global minimum. In the SA process, the calculation of Jacobian derivatives can be avoided because no preferred searching direction is required as in the case of the traditional algorithms. We apply SA technology for airborne EM inversion by comparing the inversion with a thermodynamic process, and we discuss specifically the SA procedure with respect to model configuration, random walk for model updates, objective function, and annealing schedule. We demonstrate the SA flexibility for starting models by allowing the model parameters to vary in a large range (far away from the true model). Further, we choose a temperature-dependent random walk for model updates and an exponential cooling schedule for the SA searching process. The initial temperature for the SA cooling scheme is chosen differently for different model parameters according to their resolvabilities. We examine the effectiveness of the algorithm for airborne EM by inverting both theoretical and survey data and by comparing the results with those from the traditional algorithms.

The airborne electromagnetic discovery of the Detour zinc‐copper‐silver deposit, northwestern Québec

Geophysics ◽  
1981 ◽  
Vol 46 (9) ◽  
pp. 1278-1290 ◽  
Author(s):  
L. E. Reed
Keyword(s):  
Volcanic Rocks ◽  
Channel Response ◽  
Copper Sulfides ◽  
Input System ◽  
Diamond Drill ◽  
Geophysical Surveys ◽  
Airborne Electromagnetic ◽  
Airborne Em ◽  
Two Bodies

In June 1974, a diamond drill operated for Selco Mining Corp. intersected zinc‐copper sulfides in Brouillan Township in northwestern Québec. To date, two bodies have been outlined. These bodies were discovered during a ground follow‐up of a Mark VI Input® electromagnetic (EM) survey. The Input survey covered an area selected on the basis of regional geology and local outcrops of acid volcanic rocks. Conductors were identified that appeared to be associated with potentially favorable geology. They were selected for ground follow‐up. One was the discovery zone. The airborne responses over the zone were less encouraging than those often observed over highly conductive massive sulfides. The low apparent conductivity‐thickness (5 mhos) was suggestive of conductive overburden. However, the character of the profiles suggested a bedrock source. Ground geophysical confirmation identified a drill target. Subsequent to the discovery, more intensive geophysical surveys, both ground and airborne, were carried out. The best EM response suggested a confined source within a much larger mineralized halo. Weaker ground EM response from the halo correlated with the early channel response of the Input system. An airborne EM survey conducted in 1958 over the same area identified both conductive zones. However, they were not followed up. Only with later advances in exploration philosophy, geologic appreciation, and instrumentation were the conductive zones recognized as viable exploration targets.

scholarly journals Combining efficiency and innovation to enhance performance: Evidence from firms in emerging economies

2018 ◽  
pp. 1-17 ◽  
Author(s):  
Xiaowen Tian ◽  
Vai Io Lo ◽  
Xiaoxuan Zhai
Keyword(s):  
Emerging Economies ◽  
Best Management Practices ◽  
Management Practices ◽  
Data Set ◽  
Best Management ◽  
The World Bank ◽  
Combining Efficiency ◽  
Low Levels ◽  
Enhance Efficiency ◽  
Innovation Processes

AbstractThis paper extends the resource-capability-based view in strategic management and discusses the capabilities for the firms to stay competitive in emerging economies. Faced with low levels of efficiency, technology, and skills, firms in emerging economies need to implement best management practices to overcome operational inefficiency while engage in innovation processes to address new opportunities. They have to develop the capabilities to enhance efficiency, the capabilities to undertake innovation, and the synthesis capabilities to combine the two to keep rivals at bay. The paper tests hypotheses against a data set of more than 20,000 firms from 36 emerging economies provided by the World Bank in 2012–2015 and finds strong evidence to support the arguments. The paper finds that the three sets of capabilities are positively related to productivity and, through it, financial performance.

scholarly journals Cusp-like plasma in high altitudes: a statistical study of the width and location of the cusp from Magion-4

2002 ◽  
Vol 20 (3) ◽  
pp. 311-320 ◽  
Author(s):  
J. Mĕrka ◽  
J. Šafránková ◽  
Z. Nĕmeček
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Altitudes ◽  
Data Set ◽  
Latitudinal Dependence ◽  
Merging Process ◽  
Low Altitude ◽  
Field Lines ◽  
The Magnetic Field ◽  
Dipole Tilt

Abstract. The width of the cusp region is an indicator of the strength of the merging process and the degree of opening of the magnetosphere. During three years, the Magion-4 satellite, as part of the Interball project, has collected a unique data set of cusp-like plasma observations in middle and high altitudes. For a comparison of high- and low-altitude cusp determination, we map our observations of cusp-like plasma along the magnetic field lines down to the Earth’s surface. We use the Tsyganenko and Stern 1996 model of the magnetospheric magnetic field for the mapping, taking actual solar wind and IMF parameters from the Wind observations. The footprint positions show substantial latitudinal dependence on the dipole tilt angle. We fit this dependence with a linear function and subtract this function from observed cusp position. This process allows us to study both statistical width and location of the inspected region as a function of the solar wind and IMF parameters. Our processing of the Magion-4 measurements shows that high-altitude regions occupied by the cusp-like plasma (cusp and cleft) are projected onto a much broader area (in magnetic local time as well as in a latitude) than that determined in low altitudes. The trends of the shift of the cusp position with changes in the IMF direction established by low-altitude observations have been confirmed.Key words. Magnetospheric physics (magnetopause, cusp and boundary layer; solar wind – magnetosphere interactions)

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.

The use of wavelet transforms for improved interpretation of airborne transient electromagnetic data

Geophysics ◽  
2013 ◽  
Vol 78 (3) ◽  
pp. E117-E123 ◽  
Author(s):  
Vanessa Nenna ◽  
Adam Pidlisecky
Keyword(s):  
Wavelet Transforms ◽  
Oil And Gas ◽  
Spatial Scales ◽  
Data Sets ◽  
Data Set ◽  
Topographic Features ◽  
Transient Electromagnetic ◽  
Power Maps ◽  
Southern Alberta ◽  
Cultural Noise

The continuous wavelet transform (CWT) is used to create maps of dominant spatial scales in airborne transient electromagnetic (ATEM) data sets to identify cultural noise and topographic features. The introduced approach is applied directly to ATEM data, and does not require the measurements be inverted, though it can easily be applied to an inverted model. For this survey, we apply the CWT spatially to B-field and dB/dt ATEM data collected in the Edmonton-Calgary Corridor of southern Alberta. The average wavelet power is binned over four ranges of spatial scale and converted to 2D maps of normalized power within each bin. The analysis of approximately 2 million soundings that make up the survey can be run on the order of minutes on a 2.4 GHz Intel processor. We perform the same CWT analysis on maps of surface and bedrock topography and also compare ATEM results to maps of infrastructure in the region. We find that linear features identified on power maps that differ significantly between B-field and dB/dt data are well correlated with a high density of infrastructure. Features that are well correlated with topography tend to be consistent in power maps for both types of data. For this data set, use of the CWT reveals that topographic features and cultural noise from high-pressure oil and gas pipelines affect a significant portion of the survey region. The identification of cultural noise and surface features in the raw ATEM data through CWT analysis provides a means of focusing and speeding processing prior to inversion, though the magnitude of this affect on ATEM signals is not assessed.

Nationalized incumbents and regional challengers

2015 ◽  
Vol 23 (3) ◽  
pp. 309-322 ◽  
Author(s):  
Michael Wahman
Keyword(s):  
Geographical Area ◽  
Party Systems ◽  
The Other ◽  
Systematic Research ◽  
African Countries ◽  
Data Set ◽  
Ethnic Fractionalization ◽  
Low Levels ◽  
Election Results ◽  
Opposition Parties

The African party literature, especially research prescribing to the long-dominant ethnic voting thesis, has asserted that African party systems exhibit low levels of party nationalization. However, systematic research on nationalization across parties and party systems is still lacking. This study argues that the prospects for building nationalized parties vary substantially between incumbent and opposition parties. Incumbent parties, with their access to state resources, have been successful in creating nationwide operations, even in countries where geographical factors have been unfavorable and where ethnic fractionalization is high. The analysis utilizes a new data set of disaggregated election results for 26 African countries to calculate nationalization scores for 77 parties and study the correlates of party nationalization. The results show that factors like ethnic fractionalization, the size of the geographical area, and urbanization affect party nationalization, but only in the case of opposition parties. Incumbent parties, on the other hand, generally remain nationalized despite unfavorable structural conditions.

Physico-chemical and sensory interactions of arabica coffee genotypes in different water regimes

2021 ◽  
pp. 1-9
Author(s):  
D. S. Ferreira ◽  
J. F. T. do Amaral ◽  
L. L. Pereira ◽  
J. M. S. Ferreira ◽  
R. C. Guarçoni ◽  
...  
Keyword(s):  
Block Design ◽  
Data Set ◽  
Arabica Coffee ◽  
Water Regimes ◽  
Physical Chemical ◽  
Randomized Block Design ◽  
Physico Chemical ◽  
Sensory Interactions ◽  
Specialty Coffee ◽  
Low Altitude

Abstract The production of specialty coffee has several factors and parameters that are added up in the course of production, so that the quality is expressed in the act of consumption. Based on this scenario, this study included the analysis of ten genotypes of arabica coffee, the materials being subjected to irrigated and rainfed water regimes, in a low altitude region, to identify responses for sensory and physical–chemical quality. The genotypes were evaluated in a split-plot scheme with a randomized block design, with three replications. Arabica coffee fruits were harvested with 80% cherry seeds and processed by the wet method. Subsequently, the characteristics related to physical–chemical and sensory analyses were evaluated. The genotypes of the Paraíso group showed great variability for the physical–chemical and sensory variables for rainfed and irrigated regimes. The genotypes of the Catuaí group, however, showed less variability for sensory characteristics in both cultivation environments and for physical–chemical characteristics in the irrigated regime. In the sensorial data set, the genotypes Catuaí 144 CCF and Catuaí 144 SFC (when irrigated) and Paraíso H 419-3-3-7-16-2, Paraíso H 419-3-3-7-16-11 and Catucaí 24-137 (rainfed cultivation), are more favourable to the production of specialty coffee at low altitude.

scholarly journals Wiener estimation of the Green’s function

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. W31-W44 ◽  
Author(s):  
Anton Ziolkowski
Keyword(s):  
Green’S Function ◽  
Impulse Response ◽  
Green's Function ◽  
Seismic Data ◽  
Wiener Filter ◽  
Electromagnetic Data ◽  
Transient Electromagnetic ◽  
Marine Seismic ◽  
Measured Response

I consider the problem of finding the impulse response, or Green’s function, from a measured response including noise, given an estimate of the source time function. This process is usually known as signature deconvolution. Classical signature deconvolution provides no measure of the quality of the result and does not separate signal from noise. Recovery of the earth impulse response is here formulated as the calculation of a Wiener filter in which the estimated source signature is the input and the measured response is the desired output. Convolution of this filter with the estimated source signature is the part of the measured response that is correlated with the estimated signature. Subtraction of the correlated part from the measured response yields the estimated noise, or the uncorrelated part. The fraction of energy not contained in this uncorrelated component is defined as the quality of the filter. If the estimated source signature contains errors, the estimated earth impulse response is incomplete, and the estimated noise contains signal, recognizable as trace-to-trace correlation. The method can be applied to many types of geophysical data, including earthquake seismic data, exploration seismic data, and controlled source electromagnetic data; it is illustrated here with examples of marine seismic and marine transient electromagnetic data.

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