ORCID Profile
0000-0003-4557-6567
Current Organisation
RMIT University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Electromagnetism | Geophysics | Signal Processing | Geology | Engineering/Technology Instrumentation | Electrical and Electronic Engineering | Environmental Technologies | Soil And Water Sciences Not Elsewhere Classified | Applied Hydrology (Drainage, Flooding, Irrigation, Quality, Etc.) | Igneous And Metamorphic Petrology | Groundwater Hydrology | Ore Deposit Petrology
Land and water management | Environmental and resource evaluation not elsewhere classified | Concentrating processes of other base metal ores | Land and water management | Land and water management |
Publisher: Society of Exploration Geophysicists
Date: 03-2006
DOI: 10.1190/1.2187741
Abstract: We investigate the properties of EM signals in several different response-parameter domains to identify calibration errors in helicopter electromagnetic (HEM) data. In particular, we define a dimensionless response parameter α, derived from frequency-domain data, that is numerically identical to the historic wire-loop response parameter, and is closely related to the thin-sheet and half-space response parameters. The arctangent of α is the phase ϕ of the secondary field. We further define a dimensionless litude response parameter β, calculated as the ratio between inductive limits estimated from the data and from system geometry. The inductive limit calculated from geometry provides an initial altitude correction to the data litudes. Additional data corrections further correct phase effects and altimeter variations. The litude and phase errors in calibration become independent differences between the data and the fitted model in the ϕβ domain. This investigation was undertaken in the response-parameter domain rather than in the data domain, allowing the analysis to be independent of absolute values of conductivity and system frequencies. Statistical analysis in the ϕβ domain of recently acquired data suggests that litude calibration errors in HEM data may cause fitted models to have systematic depth errors of 1 to 2 m for near-surface conductors variable altitude measurement errors are about 1.5 m over seawater.
Publisher: Society of Exploration Geophysicists
Date: 11-2009
DOI: 10.1190/1.3237143
Abstract: Bird attitudes, with roll, pitch, and yaw angles, are required for modeling the measured electromagnetic response of the earth. Global Positioning System (GPS) antennas can be used in airborne electromagnetic (AEM) systems to monitor airborne platform attitude and bird maneuver. We have found evidence from photographic sequences that four GPS antennas, three on the bird and one on the aircraft, generally are adequate for angular and altitude geometry control. The mounting system for the bird frame introduces vibration noise. We have developed a model that predicts bird maneuver from the use of GPS antennas already present during routine airborne surveys. The bird motion, whether inline or crossline, is modeled from the difference between the aircraft location and the mean location of the bird. This also accurately predicts the roll of the bird when an inline yoke mounting is used. The minimum number of GPS antennas required to monitor the motion of a cylindrical electromagnetic (EM) bird typical of frequency-domain systems is two, one on the aircraft and one on the bird. We have defined optimum locations of GPS antennas to enable geometric monitoring of towed-bird systems. The findings suggest that the bird be mounted with two aerodynamically efficient GPS antennas, one on the nose and one on the tail. This enables the measurement of the pitch and yaw of the bird, with roll deduced using the third GPS on the helicopter.
Publisher: Society of Exploration Geophysicists
Date: 11-2011
Abstract: Our research introduced a method to monitor saturation in the near surface. In agricultural settings, methods measuring electrical conductivity can provide useful information about soil type, moisture content, and salinity extent. Electrical conductivity meters have been used in a number of studies to determine soil properties in a qualitative sense. We examined the range of structures in which the use of low-induction number instruments can be used successfully to determine layered-earth electrical conductivity. We used an inversion routine which employs a Bayesian modification to the ridge-regression technique with a priori conductivity assumptions typical of agricultural areas. We performed joint inversion of horizontal and vertical dipole configurations at two coil separations for layer over half-space models with electrical properties of silt, loam, clay, and saline waters. Generally, the inversion code resolved layer thickness to better than 25% and electrical conductivity to better than 20% if the layer is less than 3-m thick. We then inverted field measurements acquired in salt-scalded areas in the Yass River Valley, New South Wales, Australia, to determine a layer over a half-space. With Kennedy’s formulation concerning the relationship between porosity, water saturation and electrical conductivity, we used the field results to predict autumn water saturation for the top layer to be 13% and the bottom layer to be 15%. In the spring, we used the field results to predict saturation of 50% for the top layer and 51% for the bottom layer, leading to a seasonal variation in soil saturation of approximately 36%. Predicted saturation was spatially consistent across the traverse line, suggesting that the developed methodology was successful.
Publisher: Society of Exploration Geophysicists
Date: 05-2007
DOI: 10.1190/1.2717498
Abstract: We aim to develop a quantitative method for recalibration of historic helicopter electromagnetic data sets. Recent research has shown that frequency-domain helicopter electromagnetic data collected over a conductive half-space such as calm seawater can be used to correct system calibration errors. However, most historic surveys consist only of data collected over land, where the conductive half-space assumption is rarely justified. We estimate the required recalibration parameters by analyzing systematic misfits in the inversion of statistically chosen measures of historic data. Our method requires the identification, within the survey area, of a zone of conductive responses that are reasonably uniform. From this zone, a set of altitude-corrected median responses are estimated. These are inverted using geologically specifiedconstraints to obtain a best-fit layered earth model. Systematic inconsistencies between the median measured altitude and the inverted depth to surface are attributed to altitude error. Remaining frequency-dependent fitting errors are assumed to be the calibration errors. We tested the method with partial success on helicopter electromagnetic data sets collected over uniform deep sediments where seawater data were also available and two different inland surveys over multiple lithologies in one general area. At high frequencies, our method works reliably. Recalibration of low-frequency data is not possible if the area used as a reference consists of moderate or poor conductors. In this case, data litudes are small and are greatly affected by imperfect drift and magnetic susceptibility corrections. Historic helicopter electromagnetic data may require litude rescaling up to 20%–30%, with phase shifts of up to 3°.
Publisher: Society of Exploration Geophysicists
Date: 11-2016
Abstract: We have first analyzed the ability of polarizable and superparamagnetic thin sheets in the near surface to fit airborne electromagnetic (AEM) data using data from western Tasmania. Then we analyzed the results of such fitting in the context of geologic mapping and available ground induced polarization (IP) data. Small to large IP effects were found to considerably improve the fit to the observed AEM data, and the overall fitted IP parameters were spatially consistent. However, the locations of anomalous IP parameters were quite distinct from anomalies in other geophysical data. The airborne chargeability highs were adjacent to or surrounded the ground chargeability highs in the five cases analyzed from Tasmanian data. Modeling using the established Cole-Cole physical property values for sulfides predicts that an inductive airborne system is insensitive to many conventional IP targets, unless the mineral grain size is substantially less than 1 mm. In the cases in which airborne IP responses were adjacent to ground IP targets, we hypothesized that the airborne IP may be finer grained minerals in an alteration halo surrounding the sulfide sources of the large ground IP anomalies. Surficial clays encountered in drillholes did not have significant ground or airborne IP responses. A companion paper comes to a similar conclusion using ground and airborne data from a copper deposit in New South Wales.
Publisher: Society of Exploration Geophysicists
Date: 07-2018
Abstract: We investigate an algorithm for 3D time-domain airborne electromagnetic (AEM) inversion based on the finite-volume (FV) method and direct Gauss-Newton optimization, where we obtain high efficiency by constraining the modeling volume to the AEM volume of influence (VOI) of a 3D source within the earth, rather than using the larger VOI of the AEM system. A half-space or layered earth is used to model the background field in the time domain, taking into account the transmitter waveform through convolution. Assuming that the 3D source of any secondary field detected at a survey point lies within the moving VOI of the airborne system, we conduct time-domain forward modeling and Jacobian calculation using an FV method within the 3D source VOI that requires a small number of cells for discretization. A local mesh and direct solver are shown to further speed up the computation. A synthetic isolated synclinal conductor inversion shows good agreement with the model geometry and provides a good fit to the data contaminated with noise. A synthetic multiple-body model inversion was also quite successful, showing that our algorithm is effective and about four times faster than inversion using the total-field method. Finally, we inverted GEOTEM data over the Lisheen deposit, where our inversion result was consistent with the published geology.
Publisher: Wiley
Date: 05-2001
Publisher: Informa UK Limited
Date: 03-2013
DOI: 10.1071/EG12048
Publisher: Informa UK Limited
Date: 12-2010
DOI: 10.1071/EG10022
Publisher: Society of Exploration Geophysicists
Date: 11-2016
Abstract: We have evaluated the mapping of polarizable material using a Cole-Cole model to fit second-order effects in concentric-loop airborne electromagnetic system responses. At Lewis Ponds in New South Wales, an inverted ground dipole-dipole array data has accurately imaged in 3D disseminated sulfide extending above and around ore grade massive sulfides. The polarizable zone is present in the near-surface, where, from modeling, airborne systems may have sensitivity to the small inductive induced polarization effects. Although the inverted chargeability measured from galvanic current injection into the ground was spatially coincident with the mineralized target, the estimated chargeabilities from induced polarization effects in an airborne versatile time-domain electromagnetic survey were substantially displaced to the east. The airborne induced polarization response may be associated with finer grained mineralization in the hanging wall of the sulfide deposits, or have a quite different source, such as clays associated with faulting.
Publisher: Society of Exploration Geophysicists
Date: 09-2020
Abstract: All available inversion software for airborne electromagnetic (AEM) data can at a minimum fit a nondispersive conductivity model to the observed inductive secondary field responses, whether operating in the time or frequency domain. Quasistatic inductive responses are essentially controlled by the induction number, the product of frequency with conductivity and magnetic permeability. Recent research has permitted the conductivity model to be dispersive, commonly using a single Cole-Cole parameterization of the induced polarization (IP) effect but this parameterization slows down and destabilizes any inversion, and it does not account for the need for dual or multiple Cole-Cole responses. Little has been published on inverting AEM data affected by frequency-dependent magnetic permeability, or superparamagnetism (SPM), usually characterized by a Chikazumi model. Because the IP and SPM effects are small and are usually only obvious at late delay times, the aim of our research is to determine if these IP and SPM effects can be fitted and stripped from the AEM data after being approximated with simple dispersive models. We are able to successfully automate a thin-sheet model to do this stripping. Stripped data then can be inverted using a nondispersive conductivity model. The IP and SPM parameters fitted independently to each independent measured decay to provide stripping are proven to be spatially coherent, and they are geologically sensible. The results are found to enhance interpretation of the regolith geology, particularly the nature and distribution of transported materials that are not afforded by mapping conductivity/conductance alone.
Publisher: Society of Exploration Geophysicists
Date: 2008
DOI: 10.1190/1.3059158
Publisher: American Geophysical Union (AGU)
Date: 27-06-2014
DOI: 10.1002/2014GL060150
Publisher: Society of Exploration Geophysicists
Date: 09-2020
Abstract: 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.
Publisher: Society of Exploration Geophysicists
Date: 05-2018
Abstract: The predominant signals of audio-frequency magnetotellurics (AMT) are called sferics, and they are generated by global lightning activity. When sferic signals are small or infrequent, measurement noise in electric and magnetic fields causes errors in estimated apparent resistivity and phase curves, leading to great model uncertainty. To reduce bias in apparent resistivity and phase, we use a global propagation model to link sferic signals in time series AMT data with commercially available lightning source information including strike time, location, and peak current. We then investigate relationships between lightning strike location, peak current, and the quality of the estimated apparent resistivity and phase curves using the bounded influence remote reference processing code. We use two empirical approaches to preprocessing time-series AMT data before estimation of apparent resistivity and phase: stitching and stacking (averaging). We find that for single-site AMT data, bias can be reduced by processing sferics from the closest and most powerful lightning strikes and omitting the lower litude signal-deficient segments in between. We hypothesized that bias can be further reduced by stacking sferics on the assumptions that lightning dipole moments are log-normally distributed whereas the superposed noise is normally distributed. Due to interference between dissimilar sferic waveforms, we tested a hybrid stitching-stacking approached based on clustering sferics using a wavelet-based waveform similarity algorithm. Our results indicate that the best approach to reduce bias was to stitch the closest and highest litude data.
Publisher: Society of Exploration Geophysicists
Date: 07-2010
DOI: 10.1190/1.3431738
Abstract: High-altitude data are used to calibrate a least-squares recursion filter that estimates the continually changing primary field of an airborne electromagnetic (AEM) system. The coupling changes in fixed-wing towed-bird systems generate “geometry noise” that in the on-time can be much larger than the ground secondary response. The LSQ filter accurately predicts the high-altitude primary field of a fixed-wing system. The filter is then applied to survey-altitude data to estimate the primary field for subsequent subtraction. After removing the primary field, a spatially consistent difference is detected over a range of delay times, as would be expected from geologic responses. A map of decay constants is produced for the survey area using the data corrected by the predicted primary field. Comparing these time constants with those computed from the conventional method, the maximum decay constant detectable was seven times larger. Thus, the new process can characterize conductors that are seven times more conductive than the conventional processing method. The residual primary field occurs at relatively high frequencies compared to targets of interest. At low frequencies [Formula: see text], we estimate that 28% of the survey-altitude primary field remains whereas only 1% of calibration flight primary is not predicted.
Publisher: Society of Exploration Geophysicists
Date: 03-2011
DOI: 10.1190/1.3553480
Abstract: Electromagnetic survey methodology is adapted to use the electric component to directly detect buried resistors and map resistivity contrasts in the near surface. System implementations do not require ground contact because they use capacitive electric-field sensors and an inductive source and may be operated at walking pace. This study outlined theoretical basis, computational modeling, and verification for the methodology. The systems are designed to operate at low enough frequency that any responses are at the resistive limit as such, the electric fields they measure are insensitive to horizontal layering and absolute conductivity. A surface integral equation algorithm is used to model regular discrete objects in a half-space. Anomalies are controlled by geometry and lateral resistivity contrast rather than by absolute resistivity values. A prototype electrode array system called CARIS 1 reliably detects resistive objects submerged in a saltwater tank, and the measured responses are consistent with numerical modeling. These results provided the basis for further development of the CARIS II system with flexible geometry that is adaptable to detect resistive or conductive targets in any background environment. CARIS is designed to be useful where conventional electromagnetics, ground-penetrating radar, and conventional resistivity face difficulties or fail, and it has easily detected a range of buried targets in the near surface. However, it is quite sensitive to disturbed ground and surface undulation and inhomogeneity.
Publisher: Society of Exploration Geophysicists
Date: 09-2012
Abstract: A major impediment in the path toward airborne induced polarization (IP) is an effective method to quantify data from inductive sources, such as those used in airborne electromagnetic systems. We modeled inductive IP using a combination of Warburg and exponential decay models as a basis for fitting electromagnetic data from ground time-domain electromagnetic (TEM) and airborne versatile TEM (VTEM) surveys. Observed decays were deconvolved into electromagnetic and IP constituents by constrained least-squares fitting of basis functions modified to account for transmitter waveforms. The method was confirmed through synthetic modeling of 2D and 3D structures, and when applied to ground TEM or airborne TEM data, obtained an estimate of apparent chargeability at each station or fiducial. In the case of a VTEM survey in Africa, the apparent chargeabilities mapped graphitic sediments and provided spatially consistent indications of clay concentrations. A limitation on this airborne IP for airborne applications is motion noise, which places a lower limit on usable base frequency and begins to significantly affect the signal at the later delay times, when IP effects are most visible.
Publisher: Informa UK Limited
Date: 03-2015
DOI: 10.1071/EG14045
Publisher: Elsevier BV
Date: 12-2016
Publisher: Society of Exploration Geophysicists
Date: 07-2010
DOI: 10.1190/1.3483101
Abstract: Most airborne electromagnetic (AEM) data are processed using successive 1D approximations to produce stitched conductivity-depth sections. Because the current induced in the near surface by an AEM system preferentially circulates at some radial distance from a horizontal loop transmitter (sometimes called the footprint), the section plotted directly below a concentric transmitter-receiver system actually arises from currents induced in the vicinity rather than directly underneath. Detection of paleochannels as conduits for groundwater flow is a common geophysical exploration goal, where locally 2D approximations may be valid for an extinct riverbed or filled valley. Separate from effects of salinity, these paleochannels may be conductive if clay filled or resistive if sand filled and incised into a clay host. Because of the wide system footprint, using stitched 1D approximations or inversions may lead to misleading conductivity-depth images or sections. Near abrupt edges of an extensive conductive layer, the lateral falloff in AEM litudes tends to produce a drooping tail in a conductivity section, sometimes coupled with alocal peak where the AEM system is maximally coupled to currents constrained to flow near the conductor edge. Once the width of a conductive ribbon model is less than the system footprint, small litudes result, and the source is imaged too deeply in the stitched 1D section. On the other hand, a narrow resistive gap in a conductive layer is incorrectly imaged as a drooping region within the layered conductor below, the image falsely contains a blocklike poor conductor extending to depth. Additionally, edge-effect responses often are imaged as deep conductors with an inverted horseshoe shape. Incorporating lateral constraints in 1D AEM inversion (LCI) software, designed to improve resolution of continuous layers, more accurately recovers the depth to extensive conductors. The LCI, however, as with any AEM modeling methodology based on 1D forward responses, has limitations in detecting and imaging in the presence of strong 3D lateral discontinuities of dimensions smaller than the annulus of resolution. The isotropic, horizontally slowly varying layered-earth assumption devalues and limits AEM’s 3D detection capabilities. The need for smart, fast algorithms that account for 3D varying electrical properties remains.
Publisher: Society of Exploration Geophysicists
Date: 11-2017
Abstract: Superparamagnetic (SPM) effects are not uncommon in ground and airborne electromagnetic (AEM) geophysical data, with sources in the regolith typically being maghemite grains. Using laboratory parameters for maghemite and the Néel equation, a typical geophysical electromagnetic (EM) system is only sensitive to maghemites with dimensions in the 9–12 nm range. The power-law decay observed in a [Formula: see text] system depends on the magnetic nanoparticle volume distribution: Log normally distributed volumes centered on the detection window produce approximately [Formula: see text] decays after the electromagnetic responses have vanished. If most of the nanoparticles are smaller than the center of the system sensitivity, the power-law decays faster than the [Formula: see text] result, if most nanoparticles are larger, a response slower than [Formula: see text] results. Geologic origins of regolith maghemite favor a thin-layer geometry in the near surface. Shape-demagnetization effects imply that SPM responses observed will only arise from magnetization in the horizontal plane. For a ground transmitter, this is the very small area directly under the transmitter loop wire, causing only locally detectable effects. For an airborne transmitter, an extensive radial ring in which the magnetic field is subhorizontal is not demagnetized, and this results in detectable SPM airborne anomalies. For SPM sources in hard rock, a magnetization model consisting of spherical particles enclosed in a finite volume is adapted for SPM. This model shows that the falloff in SPM litude with airborne system altitude is rapid for surficial and finite-bedrock sources. As a result, fixed-wing surveys with a transmitter at a 90 m or higher altitude is much less likely to show SPM effects in the EM data. Because the secondary magnetic field of spherical particles is parallel to the transmitter dipole source direction at a colocated receiver, the model explains the empirical observation that concentric loop AEM systems do not detect any [Formula: see text]-component of an SPM response.
Publisher: Society of Exploration Geophysicists
Date: 09-2013
Abstract: The cores of high-grade nickel and copper sulphides appear as “perfect conductors” to most electromagnetic (EM) and airborne electromagnetic (AEM) systems, because they have bulk electrical conductivities of the order of [Formula: see text]. The EM response of these highly conductive cores is essentially undetectable with off-time measurements or when using nonrigid towed-bird systems. Compact AEM systems with accurate primary field bucking and on-time or in-phase measurements are sensitive to perfect conductors, but are incapable of detecting deep targets. Using a GPS system to define geometry, calculations suggest that it should be easy for an AEM system to detect “perfect conductors” provided the receiver was several hundred meters distant from the transmitter. A twin (Gemini) aircraft test was undertaken to test this concept in 2005. The field test successfully demonstrated detection of very conductive targets. Errors associated with geometric changes were better than 0.5% of the primary field at 400 m separation, allowing detection and characterization of the 30 Hz, in-phase response of small and extended conductors. The test shows that a 200 × 100 m very-strongly conductive thin-sheet target would be detectable to depths of 200 m below surface using off-the-shelf technology. Larger conductors would be detectable at greater depths.
Publisher: Society of Exploration Geophysicists
Date: 11-2008
DOI: 10.1190/1.2976791
Abstract: Measuring a transmitter-current waveform provides critical data unavailable for some airborne electromagnetic (AEM) systems yet needed to model AEM data quantitatively. We developed a novel experimental method of measuring an airborne transmitter waveform by monitoring the current induced in a closed, multiturn, insulated ground loop of known inductance [Formula: see text] and resistance [Formula: see text]. The transmitter waveform of five different time-domain systems is deconvolved from the measured ground-loop response when excited by the primary electromagnetic field of the AEM system. In general, our measurements agree well with contractor-described transmitter current waveforms, although crucial differences exist between our deconvolved waveforms and those described in the literature. Using the pulse-per-second feature of a GPS antenna, the ground loop can monitor the frequency drift of a frequency-domain system. The ground loop behaves like a lossy electric-field antenna when the resistance closing the ground loop is too large. This leads to negatives in the response of coincident-loop systems without including induced polarization effects. After observing exponentially decaying, oscillating-current responses in high-resistance ground loops, we model the observed current with an LRC circuit whose resistance and capacitance represent generalized effective antenna and free-space values. Our model predicts responses that closely match the d ed oscillations seen in the airborne response during flyover however, it does not work well on conductive ground.
Publisher: Society of Exploration Geophysicists
Date: 14-02-2023
Abstract: SUMMARY The underlying Cole-Cole model of the frequency dependence of complex conductivity and resistivity predicts two time constants that are not identical but which are related to each other. The shorter time constant [Formula: see text] predicts the current response to a voltage step and, in various models of a mineralized grain, is related to the intrinsic properties of the polarizable component, whereas the longer time constant [Formula: see text], which predicts the voltage response to a current step, is dependent on intrinsic material properties and also the relative volume of polarizable material as defined through chargeability. As a consequence, although we agree with most of the conclusions of the original paper, the specification [Formula: see text] instead of [Formula: see text] in reference tables will simplify.
Publisher: Society of Exploration Geophysicists
Date: 2005
DOI: 10.1190/1.2112391
Abstract: The last two decades saw major advances in data collection, processing, and interpretation of electrical and EM data. Lower transmitter frequencies for airborne time-domain EM systems have made possible surveys in areas where conductive cover previously screened basement conductors. As with every other branch of technology, the evolving speed of the silicon chip and of streaming data to hard disk has revolutionized data collection and noise reduction processing. Major advances have been made on increasing the signal-to-noise ratios in ground EM data acquisition systems. Full-waveform recording and the use of multiple receivers are becoming common for ground EM techniques. Previously intractable 2D and 3D data inversions are now slowly becoming available. Finally, controlled-source EM techniques are now being used to detect and characterize hydrocarbon-bearing reservoirs in deepwater areas.
Publisher: Unpublished
Date: 2012
Publisher: Wiley
Date: 2010
Publisher: Society of Exploration Geophysicists
Date: 11-2016
Abstract: The primary aim of my research is to improve the characterization of induced polarization (IP) responses in airborne electromagnetic (AEM) survey data. The principal objectives are to test alternative methodologies for quantitative modeling and inversion to extract the spatial variation of IP parameters using the inductively thin-sheet model. The methods tested first fit, by nonnegative least squares, an AEM decay to the early delay time data, using thin-sheet basis functions. This modeled AEM decay is assumed to represent the IP source. It is then convolved with a few Cole-Cole models spanning the range of parameter sensitivity to get IP basis functions appropriate for the AEM excitation. Method 1 fits a linear sum of several AEM basis functions plus one IP basis function at a time and chooses the model with least-fitting error at late delay times. Method 2 fits a linear sum of several IP and several AEM basis functions. Both methods fit IP affected airborne data well, with normalized fitting errors being reduced by a significant factor when IP affects the data and is taken into account. Using penalty weights, superparamagnetic (SPM) effects can be simultaneously estimated in the fitting process. Without such weighting, SPM and IP parameter estimations are unstable. Cole-Cole models predict that the sensitivity of inductive airborne IP collected at 25 or 30 Hz base frequency indicates little overlap with galvanic ground IP collected with a 0.125 Hz waveform. Many easy IP sulfide targets with IP physical properties determined by ground surveys are predicted not to have a detectable airborne IP response. Clays, however, are predicted to have a small detectable background response that for airborne data would not be well-fitted by a single Cole-Cole response.
Publisher: Informa UK Limited
Date: 03-2011
DOI: 10.1071/EG10017
Publisher: Elsevier BV
Date: 03-1995
Publisher: Informa UK Limited
Date: 09-2014
DOI: 10.1071/EG13064
Publisher: Society of Exploration Geophysicists
Date: 07-2008
DOI: 10.1190/1.2943189
Abstract: Quantitative interpretation of time-domain airborne electromagnetic (AEM) data is h ered by uncertainty in altimetry, system geometry, transmitter waveform, data averaging, and timing. We present a simple calibration method that serves to define these issues by the use of a closed multiturn loop of known electrical and physical properties that is insulated from the ground beneath it. By predicting the secondary response of the AEM receiver and comparing it with the measured data, we have identified and quantified systematic errors mentioned above in several systems. In addition, we identify an alternative subprocess that uniquely calculates altimeter and geometry errors by measuring the current induced in a ground loop of known properties and comparing it with predictions. The ground-loop method is used best over resistive cover to minimize limitations caused by nonuniform conductive ground and is a calibration tool that makes AEM data consistent with quantitative models. Fluctuating geometric errors caused by bird swing limit the accuracy of applying the geometry corrections from one flyover to an entire survey.
Publisher: Informa UK Limited
Date: 03-2015
DOI: 10.1071/EG14036
Publisher: Society of Exploration Geophysicists
Date: 11-2016
Abstract: Our aim was to confirm the ability of polarizable and superparamagnetic (SPM) thin sheets in the near surface to improve the model fit of airborne electromagnetic data. Our method was to fit induced polarization (IP) effects with Cole-Cole complex conductivity and fit SPM effects with Chikazumi complex permeability. Surficial conductors were assumed to be the source of the conductivity and IP effects. In this case history from Lac Brûlé, Quebec over an anorthosite intrusion, small to large IP effects were found to be essential to fit most of the observed data. In some areas, it was also possible to separate SPM effects from IP effects in the data. Most IP effects in this unusually polarizable area were adequately fit with a distributed decay characterized with a frequency dependence of [Formula: see text], but some required a sharper response characterized by [Formula: see text]. In general, fitted IP time constants were anticorrelated with fitted frequency dependence, with short time constants fitted to the larger [Formula: see text] values and vice versa. SPM effects were detected in a small but significant fraction of the data, and appear to be spatially related to static magnetic anomalies. The SPM in this case is presumably related to fine-grained rock magnetism, rather than the more common case of weathering products.
Location: South Africa
Start Date: 2005
End Date: 2013
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2003
End Date: 06-2006
Amount: $333,300.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2003
End Date: 04-2006
Amount: $170,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 06-2004
End Date: 06-2006
Amount: $150,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2005
End Date: 06-2014
Amount: $24,450,000.00
Funder: Australian Research Council
View Funded Activity