Transmitter Loop Research Articles

Turning off low and high currents in a transmitter loop used in the transient electromagnetic method

ABSTRACTIn near‐surface transient electromagnetic studies, it is desirable to measure the transient response starting from the earliest possible time. This requires the current in the transmitter loop to be switched off quickly, which necessitates working with a low transmitter current. As for deep‐target transient electromagnetic studies, the transmitter current is as high as possible. The transmitter current's turn‐off waveform and total duration affect the transient voltage response, especially at early times, which is to be accounted for when interpreting transient electromagnetic data. This article discusses the difference in switching off low and high current in a horizontal loop used as the source of the primary magnetic field in the transient electromagnetic method. Low and high currents are turned off in fundamentally different ways. When the current to be switched off is low, the loop can be represented as a symmetric combination of two transmission lines grounded at the middle of the loop perimeter. Such a representation of a loop allows calculating the current turn‐off waveform at any point of the loop. The waveform and total duration of switching off a low current does not depend on its magnitude, but is determined by the period of natural oscillations of the current in the loop and the resistance of a shunting resistor. Switching off a low current in a loop can be represented as the sum of stepped current waves travelling along the loop wire. As a consequence, the current at different points of the loop perimeter is turned off at different times. In contrast to a low current, a high current is switched off linearly in time and synchronously at all points of the loop perimeter. The wave phenomena appear only at the very beginning of the current shutdown for a time interval that is much less than the total current turn‐off duration. Presentation of the loop using a simple lumped‐circuit model predicts the waveform and duration of the high current turn‐off that coincide with the measured ones. There are two reasons why the article may be of interest to those engaged in the theory and/or practice of electromagnetic geophysical methods. First, it contributes to a general understanding of how the current in the transmitter loop is turned off. Second, the article shows how the parameters of a transmitter loop determine the current turn‐off duration and thus the minimum depth of the transient electromagnetic sounding method.

Mapping sea water intrusion in coastal area using time-domain electromagnetic method with different loop dimensions

Time Domain Electromagnetic (TDEM) method has been widely used in mapping and assessment of groundwater resources and sea water intrusion along coastal alluvial plains. TDEM soundings were used to define aquifer zones in the alluvial aquifer at Al Khoud coastal area in North Oman. The main aquifer zones, composed of clean gravels, clayey gravels, and cemented gravels, could be identified, along with the basal contact of the aquifer. The TDEM data were also used to map the depth to the interface between freshwater and saline-water along the coast. The inland extents and thickness of the saline water intrusion zone were mapped along two sets of TDEM profiles. The depth to the intrusion zone was investigated using different transmitter loop sizes. Quality assurance of the data was done by comparing the resistivity distribution derived from TDEM with the electrical conductivity and resistivity logs from available well logging data in the study area. TDEM proved to be a successful tool for mapping saline zones and fresh water in arid environment with high depth of penetration and speed of field operation.

Magnetic Field Penetration Into a Metal Enclosure Using an ELF/VLF Loop Antenna

The ability of extremely and very low frequency (ELF/VLF, 0–30 kHz) radio waves to penetrate conductive media is well established. Magnetic field penetration into a thin but highly conductive box using an ELF/VLF loop antenna transmitter is investigated. The work is relevant for electromagnetic shielding of ELF/VLF sensors, defect detection, inductive power transfer, and through container imaging. Analytical solutions are reviewed for related shielding problems, however, determining the penetration through a realistic shield geometry and finite sized near-field source requires a numerical approach. Surface integral equation (SIE) methods are well suited for shield modeling due to the low surface area to volume ratio of the shield. Method of moment techniques have been successfully applied to solving SIEs in the past, however, enforcing algorithm stability at low frequencies is known to require considerable effort. To alleviate the low-frequency concerns, a high-order locally corrected Nystrom (LCN) scheme is utilized to solve an SIE based on an augmented Muller formulation of Maxwell's equations. To validate the LCN simulations, an experiment is conducted using a loop antenna inside a 1.2 m aluminum cube of 2.7 mm thickness with an external ELF/VLF loop transmitter. Experimental results are shown to match within 3 dB of the LCN code predictions.

Characterization of TDEM System With SQUID and Fluxgate Magnetometers for Geophysical Applications

This article describes the characterization of the SQUID-based time domain electromagnetic (TDEM) system for use in geophysical applications. This system has been characterized near the laboratory where the background noise, especially the cultural noise, is relatively low. A transmitter loop in the form of a square (2 × 2 m) with the excitation current of 0.212 A in the form of modified square pulses with a frequency of 2.5 Hz has been used to induce eddy currents in a nearby conducting target. A three-axes low Tc dc SQUID magnetometer and its associated fast readout electronics have been used to record the transient response of the target. Meanwhile, as part of this developmental work and to get the field experience, the TDEM measurements have been performed in the field with transmitter loop size of 100 × 100 m and fluxgate magnetometer as a receiver. Here, we observed that the decay of the secondary magnetic field has always unexpectedly reached a negative value even at the earlier time windows. Subsequently, the TDEM experiments with fluxgate as the receiver have been repeated with the same configuration as done in the past with SQUID, and the performance of the magnetometers, such as fluxgate and SQUID, have been compared. The experimental results were analyzed in detail and show that the fluxgate magnetometer behaves as the combination of magnetic field sensor and induction coil at earlier decay times, and magnetic field sensor only at later decay times.

Fast Resistivity Imaging of Transient Electromagnetic Using ANN

Transient electromagnetic (TEM) soundings are being increasingly used in engineering applications of environmental and regional surveys and shallow metal detection. Efficient and real time of the processing of the observed TEM data is the trend for the engineering geophysical prospecting and detection instrument in modern times. This letter presents a fast resistivity imaging method of TEM using artificial neural networks. The input–output mapping relations of neural networks are established based on the TEM response characteristics under different transmitter loop devices. The built network could map the recorded TEM data and quickly obtain the resistivity image. The proposed method offers accuracy and fast computation for resistivity imaging, and only 9.003 s costs for the calculation of 142 measured points’ data. Feasibility and technical attractiveness of the proposed method in fast resistivity imaging of TEM mean that it is well suited for instantaneous of survey results to a client. The proposed TEM imaging method can be used in real time so that the recorded TEM data can be calculated without retraining, which avoids time-consuming iteration and inversion computation.

TEM apparent resistivity imaging for grounding grid detection using artificial neural network

Transient electromagnetic (TEM) method is a reliable means of non-destructive testing for fault diagnosis of grounding grid in substation. In view of the small transmitter loop of the TEM system and many measuring points and survey lines of grounding grid detection in substation. This study presents a fast solution to TEM apparent resistivity imaging for grounding grid detection using artificial neural networks. The input -output mapping relation of neural network is established based on TEM response characteristics of the grounding grid. The built network could map the recorded TEM data of grounding grid detection and quickly obtain the resistivity image. The proposed method offers accuracy and fast computation for the resistivity imaging of grounding grid. Feasibility and technical attractiveness of the proposed method in fast imaging of apparent resistivity is investigated with the measurement of grounding grids in the actual substations. It can be used in real time so that the recorded TEM data in substation can be calculated without re-training, which avoids time-consuming inversion computation. The rapid processing of massive data and submitting the detection results of the grounding grid to customers rapidly and in real time, which is expectation for a modern power industry.

Delineating Lake Bottom Structure by TEM on Water Surface

Recently the development of TEM (Transient Electromagnetic) provides higher resolution and greater exploration depth than ever before and it is time to consider whether this advanced TEM technique can be applied to under-water mapping. About 250 TEM soundings have been measured within a lake of about 120m by 60m in a muddy deposits environments in southern Taiwan. For the TEM measurements the terrTEM unit (Monex GeoScope) was used with an inloop configuration, for which the receiver spacing is about 5 m and the transmitter loop is about the same size as the lake. For imaging the vertical and horizontal resistivity distribution within the deposit and the surrounding area, all sounding results were interpreted using a smooth inverse procedure. Some auger drilling and sounding were available for correlation. This led to a final model. Underneath the water bottom is mud/shale inter-bed with a depth greater than 50 m and resistivity ranging from 1 to 5 ohm-m. The depth of the clayey layer predicted by TEM data is comparable to that of drilled wells nearby, and the thick mud to the southeast suggests the lake dipping to the southeast. The success of the method depends upon the appropriate design of survey parameters; this new application is open to further refinement, both in instruments and in survey techniques.

The Impact of AEM Receiver Noise Levels on Detection, Discrimination and Resolvability of Conductive Targets

Lowering receiver noise levels of EM systems has the same benefits as increasing the transmitter signal, because detectability, discrimination and resolvability of target responses improves as the signal to noise ratio increases. Unfortunately the peak dipole moment (where peak dipole moment is considered to be the product of the peak current and the effective transmitter loop area) of TEM systems is often still perceived as being the most significant factor contributing to the signal to noise ratio. The importance of also taking into account the excitation waveform pulse width and shape when determining target response is well published. However, the quantitative effects of reducing receiver noise levels have not received much coverage in literature. Modeling experiments using real VTEM system noise samples from 2006 and 2009 indicates that a four times reduction in system noise amplitude can improve detectability of targets up to 100 m deeper and also enables target conductance and geometry to be modeled as accurately for targets up to 150 m deeper. These improvements are better than can be modeled with a simulated increase in peak dipole moment giving the same signal to noise ratio. This is most likely due to the fact that the real character of noise should be taken into account and not only the standard deviation.

A 21-dm-OP1 dB 20.3%-Efficiency -131.8-dBm/Hz-Noise X-Band Cartesian Error Feedback Transmitter With Fully Integrated Power Amplifier in 65-nm CMOS

This article presents an $X$ -band Cartesian error feedback loop transmitter (CEFLT) with a fully integrated power amplifier (PA) in a 65-nm CMOS. The extra reference path cancels the feedback signal to mitigate the inherent linearity–noise tradeoff in the conventional Cartesian feedback loop transmitter (CFLT). In this way, the nonlinearities from the feedback path are suppressed without using large attenuation, and thus the noise contribution from the feedback path is reduced as well. Compared with the conventional CFLT, the proposed CEFLT can improve the linearity without degrading the noise performance. The PA-included transmitter delivers a maximum power ( $P_{\mathrm {SAT}}$ ) of 21.4 dBm and output-referred 1-dB compression point ( OP 1 dB) of 21 dBm, with 33.3% and 30.3% PA output stage efficiency, respectively, and 22.3% and 20.3% system efficiency, respectively. Compared with the open-loop condition, the closed-loop transmitter demonstrates up to 13.6-dB suppression of adjacent channel leakage ratio (ACLR) error vector magnitude (EVM) using 4 Msps 64 quadratic-amplitude modulation (QAM) signals. The out-of-band (OOB) noise at 100 MHz is −133/−131.8 dBm/Hz for the lower and upper sidebands, respectively.

LOUPE - A Portable EM Profiling System

Loupe is a new, portable, time-domain electromagnetic system specifically designed for rapid reconnaissance and near-surface conductivity measurements. The receiver and transmitter are each carried by one person on a backpack. Loupe incorporates a 3-component coil sensor with 100 kHz bandwidth, a fast-switching transmitter loop, a simple user-interface and the ability to navigate and recover position using RTK GPS. By virtue of intelligent signal processing, carried out in real-time and in post-acquisition processing, Loupe will operate effectively in the presence of interference from power transmission lines and other sources of noise that traditionally degrade the performance of EM systems in urban areas.A completely portable time-domain EM system of this nature is unique. This paper will discuss the design and features of Loupe and likely applications for it.Here, we present an example of data from a geotechnical investigation. By the time of the conference, we expect to be able to present results from other work done with Loupe in exploration and mine projects. This system, and its results, will be compared against other techniques to illustrate the increase in near-surface resolution and speed of broadband data collection.

Capability of low-temperature SQUID for transient electromagnetics under anthropogenic noise conditions

Transient electromagnetics (TEM) is a well-established method for mineral, groundwater, and geothermal exploration. Superconducting quantum interference device (SQUID)-based magnetic-field receivers used for TEM have quantitative advantages and higher sensitivity compared with commonly used induction coils. Special applications are deep soundings with target depths [Formula: see text] and settings with conductive overburden. However, SQUIDs have rarely been applied for TEM measurements in environments with significant anthropogenic noise. We compared a low-temperature SQUID with a commercially available induction coil in an area affected by anthropogenic noise. We acquired four fixed-loop data sets with totally 61 receiver stations close to Bad Frankenhausen, Germany. The high sensitivity of the SQUID enables low noise levels, which lead to longer high-quality transient data compared with the induction coil. The effect of anthropogenic and natural noise sources is more critical for the coil than for the SQUID data. In the vicinity of the transmitter loop, systematic distortion of the coil signals occurs at early times, most probably caused by sferic interferences. We have developed 1D inversion results of both receivers that matched well in general. However, the SQUID-based models were more consistent and showed greater depths of investigation. This led to a superior resolution of deeper layers and even enabled a potential detection of thin conducting targets at up to a 500 m depth. Moreover, we find that the SQUID data inversion revealed multidimensional effects within the conductive overburden. In this regard, we applied forward modeling to analyze systematic differences between inversion results of SQUID and coil data. We determine that low-temperature SQUIDs have the potential to significantly improve the reliability of subsurface models in suburban environments. Nevertheless, we recommend combined application of both types of receivers.

A first application of a marine inductive source electromagnetic configuration with remote electric dipole receivers: Palinuro Seamount, Tyrrhenian Sea

ABSTRACTWe study a new marine electromagnetic configuration that consists of a ship‐towed inductive source transmitter and a series of remote electric dipole receivers placed on the seafloor. The approach was tested at the Palinuro Seamount in the southern Tyrrhenian Sea, at a site where massive sulphide mineralization has been previously identified by shallow drilling. A 3D model of the Palinuro study area was created using bathymetry data, and forward modelling of the electric field diffusion was carried out using a finite volume method. These numerical results suggest that the remote receivers can theoretically detect a block of shallowly buried conductive material at up to ∼100 m away when the transmitter is located directly above the target. We also compared the sensitivity of the method using either a horizontal loop transmitter or a vertical loop transmitter and found that when either transmitter is located directly above the mineralized zone, the vertical loop transmitter has sensitivity to the target at a farther distance than the horizontal loop transmitter in the broadside direction by a few tens of metres. Furthermore, the vertical loop transmitter is more effective at distinguishing the seafloor conductivity structure when the vertical separation between transmitter and receiver is large due to the bathymetry. As a horizontal transmitter is logistically easier to deploy, we conducted a first test of the method with a horizontal transmitter. Apparent conductivities are calculated from the electric field transients recorded at the remote receivers. The analysis indicates higher apparent seafloor conductivities when the transmitter is located near the mineralized zone. Forward modelling suggests that the best match to the apparent conductivity data is obtained when the mineralized zone is extended southward by 40 m beyond the zone of previous drilling. Our results demonstrate that the method adds value to the exploration and characterization of seafloor massive sulphide deposits.

Magnetic viscosity effect on TEM data of an array with a fixed transmitter loop

In this paper, we present and discuss the results of modeling of the transient induction processes observed at different distances from the center of a transmitter loop in studies of a two-layer earth in which the magnetic susceptibility of the top layer or the base depends on frequency. Profiling graphs (the offset is plotted on the abscissa, and the EMF induced in the receiver coil at a fixed time is plotted on the ordinate) show that the polarity of the EMF changes as the offset increases. For the model with a magnetic layer of any thickness, the polarity of the EMF reverses immediately after the receiver crosses the loop wire. For the model with a magnetic base, the offset at which the EMF polarity reversal occurs is the larger the greater the thickness of the layer. For both models, the EMF at a fixed time depends on the thickness of the layer and the offset. Particularly strong dependence of the EMF on layer thickness or offset is observed near the loop side. Therefore, measurements near the wire make it possible to determine the thickness of the layer in the case where it is much less than the length of the loop side. The overall effect of magnetic relaxation and transient eddy currents leads to the fact that small changes in the layer thickness or offset can lead to a dramatic change in the transient response.

Dynamic impedance compensation for wireless power transfer using conjugate power

Wireless power transfer (WPT) via coupled magnetic resonances has been in development for over a decade. However, the frequency splitting phenomenon occurs in the over-coupled region. Thus, the output power of the two-coil system achieves the maximum output power at the two splitting angular frequencies, and not at the natural resonant angular frequency. According to the maximum power transfer theorem, the impedance compensation method was adopted in many WPT projects. However, it remains a challenge to achieve the maximum output power and transmission efficiency in a fixed-frequency mode. In this study, dynamic impedance compensation for WPT was presented by utilizing the compensator within a virtual three-coil WPT system. First, the circuit model was established and transfer characteristics of a system were studied by utilizing circuit theories. Second, the power superposition of the WPT system was carefully researched. When a pair of compensating coils was inserted into the transmitter loop, the conjugate power of the compensator loop was created via magnetic coupling of the two compensating coils that insert into the transmitter loop. The mechanism for dynamic impedance compensation for wireless power transfer was then provided by investigating a virtual three-coil WPT system. Finally, the experimental circuit of a virtual three-coil WPT system was designed, and experimental results are consistent with the theoretical analysis, which achieves the maximum output power and transmission efficiency.

Electrical Resistivity Tomography and TDEM Applied to Hydrogeological Study in Taubaté Basin, Brazil

This research applies Electrical Resistivity Tomography (ERT) and Time Domain Electromagnetic Method (TDEM) to study the hydrogeology of the Taubaté basin, which is characterized by half-grabens with about 850 m of maximum sediments thickness. The study area is in Taubaté city, São Paulo State, Brazil, where the Taubaté aquifer is an important water source. The Taubaté Group is the main sedimentary package of the basin; it is formed mainly by shales that form aquicludes, and thin layers of sandstones that form the aquifer. There are 40 groundwater exploration wells in Taubaté city that provide important information. The study purpose is to characterize the geoelectrical stratigraphy of the subsurface to locate the contact between the Quaternary and Tertiary sediments and to identify the Taubaté aquifer. The ERT is used for shallow investigations (tens of meters) and the TDEM can reach a great investigation depth (hundreds of meters). Therefore, these geophysical methods are complementary. The ERT data were acquired with the pole-dipole array with 20 m of electrodes spacing and 400 m length, and the TDEM data with the central-loop array with a 200 × 200 m transmitter loop. The results permit to define the contact between the Quaternary and Tertiary sediments around 15 m depth, the Pindamonhangaba Formation between 15 m and 30 m depth and the Taubate Group between 30 m and 300 m depth. The TDEM method defined the Taubaté Group as a single geoelectric layer because the shale and the sandstone layers are all very conductive. The basement is formed by gneiss, which is a very resistive rock. The TDEM method is not able to identify a high conductor/resistor contrast. Overall, the results are consistent with the known geology and the wells information.

64-QAM 60-GHz CMOS Transceivers for IEEE 802.11ad/ay

This paper presents 64-quadrature amplitude modulation (QAM) 60-GHz CMOS transceivers with four-channel bonding capability, which can be categorized into a one-stream transceiver and a two-stream frequency-interleaved (FI) transceiver. The transceivers are both fabricated in a standard 65-nm CMOS technology. For the proposed one-stream transceiver, the TX-to-RX error vector magnitude (EVM) is less than −23.9 dB for 64-QAM wireless communication in all four channels defined in the IEEE 802.11ad/WiGig. The maximum communication distance with the full rate can reach 0.13 m for 64 QAM, 0.8 m for 16 QAM, and 2.6 m for QPSK using 14-dBi horn antennas. A data rate of 28.16 Gb/s is achieved in 16 QAM by four-channel bonding. The transmitter, receiver, and phase-locked loop consume 186, 155, and 64 mW, respectively. The core area of the transceiver is 3.9 mm2. For the proposed two-stream FI transceiver, four-channel bonding in 64 QAM is realized with a data rate of 42.24 Gb/s and an EVM of less than −23 dB. The front end consumes 544 mW in transmitting mode and 432 mW in receiving mode from a 1.2-V supply. The core area of the transceiver is 7.2 mm2.

A New Technique for Reducing Size of a WPT System Using Two-Loop Strongly-Resonant Inductors

Mid-range resonant coupling-based high efficient wireless power transfer (WPT) techniques have gained substantial research interest due to the number of potential applications in many industries. This paper presents a novel design of a resonant two-loop WPT technique including the design, fabrication and preliminary results of this proposal. This new design employs a compensation inductor which is combined with the transmitter and receiver loops in order to significantly scale down the size of the transmitter and receiver coils. This can improve the portability of the WPT transmitters in practical systems. Moreover, the benefits of the system enhancement are not only limited to the lessened magnitude of the T X & R X , simultaneously both the weight and the bill of materials are also minimised. The proposed system also demonstrates compatibility with the conventional electronic components such as capacitors hence the development of the T X & R X is simplified. The proposed system performance has been validated using the similarities between the experimental and simulation results. The power efficiency of the prototype circuit is found to be 93%, which is close to the efficiency reached by the conventional design. However, the weight of the transmitter and receiver inductors is now reduced by 78%, while the length of these inductors is reduced by 80%.

Superparamagnetism in ground and airborne electromagnetics: Geometrical and physical controls

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 amplitude 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.

On electric fields produced by inductive sources on the seafloor

The transient electromagnetic (TEM) method has recently been proposed as a tool for mineral exploration on the seafloor. Similar to airborne TEM surveys conducted on land, marine TEM systems can use a concentric or coincident wire-loop transmitter and receiver towed behind a ship. Such towed-loop TEM surveys can be further augmented by placing additional stationary receivers on the seafloor throughout the survey area. We examine the electric fields measured by remote receivers from an inductive source transmitter within a 1D layered earth model. At sea, it is conceivable to deploy either a horizontal transmitter (such as the analogous standard airborne configuration) or a more exotic vertical transmitter. Therefore, we study and compare the sensitivity of the vertical and horizontal towed-loop systems with a variety of seafloor conductivity structures. Our results indicate that the horizontal loop system is more sensitive to the thickness of a buried conductive layer and would be advantageous over the vertical loop system in characterizing the size of a shallowly buried mineralized zone. The vertical loop system is more sensitive to a resistive layer than the horizontal loop system. The vertical electric field produced by the vertical loop transmitter is sensitive to greater depths than the horizontal fields, and measuring the vertical field at the receivers would therefore be advantageous. We also conducted a novel test of a towed horizontal loop system with remote dipole receivers in a marine setting. The system was tested at the Palinuro volcanic complex in the Tyrrhenian Sea, a site of known massive sulfide mineralization. Preliminary results are consistent with shallowly buried material in the seafloor of conductivities [Formula: see text].

3D inversion of total magnetic intensity data for time-domain EM at the Lalor massive sulphide deposit

The Lalor deposit is a massive sulphide that is characterised as a stack of conductive ore lenses buried more than 600 m deep. We invert helicopter sub-audio magnetics (HeliSAM) data from Lalor collected using a ground large transmitter loop and an airborne total magnetic intensity (TMI) magnetometer measuring the time-domain electromagnetic (EM) responses. The TMI data are modelled as a projection of the anomalous field onto the earth’s magnetic field. Inversion of these data is considered a significant case study because of two challenges. First, the early-time data are contaminated by the infrastructure on the surface. Second, inverting the data with a uniform half-space as the initial model results in a mathematically acceptable, but non-geologic, model. We create workflows to overcome these difficulties. For the contaminated data, we use a locally refined mesh and a constrained inversion to recover highly conductive cells near the surface that effectively represent the infrastructure. This allows us to safely extract geologic information from the early time data. The non-uniqueness in the inversion is reduced by warm-starting the voxel 3D inversion with a more reasonable initial guess, for example, a block model from geometric inversions. Those procedures greatly improve the inversion image from the surface to the bottom of the target at Lalor, and they can easily be incorporated into the industrial production workflows.