Gianluca Fiandaca

• PhD
• Professor (Assistant) at Aarhus University

For accurate modelling of groundwater flow and transport processes within an aquifer, precise knowledge about hydraulic conductivity K and its small-scale heterogeneities is fundamental. Methods based on pumping tests, such as hydraulic tomography (HT), allow for retrieving reliable K-estimates, but are limited in their ability to image structural...

Recent instrument advancements in the transient electromagnetic (TEM) method enable waterborne applications as well as traditional ground-based surveys. We investigate a common framework to handle combined data sets from ground-based and waterborne TEM surveys under one model domain. The modeling complexity increases for two main reasons: (1) multi...

Precise information about the spatial distribution of hydraulic conductivity (K) in an aquifer is essential for the reliable modeling of groundwater flow and transport processes. In this study, we present results of a new inversion procedure for induced polarization (IP) data that incorporates petrophysical relations between electrical and hydrauli...

Transient electromagnetic (TEM) is an efficient non-invasive method to map electrical conductivity distribution in the subsurface. This paper presents an inversion scheme for three-dimensional (3D) TEM time-lapse data using a generalized minimum support norm and its application to monitoring conductivity changes over time. In particular, two challe...

Airborne systems collecting transient electromagnetic data are able to gather large amounts of data over large areas in a very short time. These data are most often interpreted through 1D inversions, due to the availability of robust, fast and efficient codes. However, in areas where the subsurface contains complex structures or large conductivity...

The interest for the Airborne Induced Polarization (AEMIP) effect has been increasing in the recent years, especially due to its advantage to investigate lithological polarization properties in large areas when compared to what can be covered in conventional ground-based galvanic time/frequency domain induced polarization surveys. Inversion of AEMI...

The Airborne Electromagnetic Induced Polarization (AEMIP) effect is being an important topic in exploration geophysics in the recent years, especially due its potentiality for mapping polarizable anomalies in large areas in comparison to the ground-based galvanic induced polarization surveys. In addition, the modeling of AEMIP has been demonstrated...

Hydrogen Sulphur (H2S) is an undesired by-product of geothermal energy exploitation. Previous studies show that H2S can be injected into the subsurface, where the interaction between injected H2S-enriched fluids and basaltic formations results in the precipitation of pyrite and other minerals such as smectite. Laboratory measurements and field inve...

Inversion of large-scale time-domain transient electromagnetic (TEM) surveys is computationally expensive and time-consuming. The calculation of partial derivatives for the Jacobian matrix is by far the most computationally intensive task, as this requires calculation of a significant number of forward responses. We propose to accelerate the invers...

Worldwide, soil contamination due to industrial activities is a major issue. One method for remediation of contaminated sites is in‐situ chemical oxidation, where an oxidizing agent is injected into the contaminated soil. Normally, monitoring wells are established in the remediation area for tracking the oxidizing agent. However, wells only provide...

S U M M A R Y We present a new algorithm for 3-D forward modelling and spectral inversion of resistivity and time-domain full-decay induced polarization (IP) data. To our knowledge, all algorithms available for handling 3-D spectral inversion of full-decay IP data use a time-domain approximation to Poisson's equation in the forward response. To avo...

The induced polarization (IP) response in airborne electromagnetic data has recently received attention due to its potential significance for mineral exploration and environmental applications, while also holding the prospect of improved geophysical models. A typical IP response produces negative transients in the late time gates. However, under ce...

With advances in data acquisition and processing methods, spectral inversion of time domain induced polarization (IP) data is becoming more common. Geological interpretation of inverted spectral parameters, for instance Cole-Cole parameters, often relies on results from systematic laboratory measurements. These are most often carried out with frequ...

With advances in data acquisition and processing methods, spectral inversion of time domain induced polarization (IP) data is becoming more common. Geological interpretation of inverted spectral parameters, for instance Cole-Cole parameters, often relies on results from systematic laboratory measurements. These are most often carried out with frequ...

Envelope detection is an integral step of the surface NMR data processing workflow. A promising approach to produce high signal-to-noise ratio envelopes involves a scheme referred to as spectral analysis (SA) envelope detection – a scheme based upon a series of discrete Fourier transforms for sliding windows of observed NMR data. This method has th...

This paper presents the results of airborne electromagnetic induced polarisation inversions using the Maximum Phase Angle (MPA) model for a helicopter time domain survey in the Quadrilátero Ferrífero area, Minas Gerais State (MG), Brazil. The inversions were conducted using a laterally constrained robust scheme, in order to decrease the difficultie...

The DC resistivity method is a common tool in periglacial research because it can delineate zones of large resistivities, which are often associated with frozen water. The interpretation can be ambiguous, however, because large resistivities may also have other causes, like solid dry rock. One possibility to reduce the ambiguity is to measure the f...

This paper presents the results of the Airborne Electromagnetic Induced Polarization (AEMIP) 1D Laterally Constrained Inversion (LCI) using the Maximum Phase Angle (MPA) re-parameterization of the Cole-Cole model for an AeroTEM HD survey in Quadrilátero Ferrífero area, MG, Brazil. The MPA LCI's were conducted using a robust inversion scheme and its...

An integral component of the surface nuclear magnetic resonance forward model involves predicting the magnitude of the transverse magnetization following excitation. To predict the transverse magnetization, the Bloch equation must be solved. Traditional surface NMR forward models solve a simplified version of the Bloch equation where the relaxation...

The signal level and shape of induced polarization responses are significantly affected by the current pulse duration and waveform. If not accounted for, this data dependency on the current will propagate trough the inversion to results rendering unquantifiable subsurface models. While this problem has been addressed in full-response induced polari...

Soil contamination from industrial activities is a large problem in urban areas worldwide. Understanding the spreading of contamination to underlying aquifers is crucial to make adequate risk assessments and for designing remediation actions. A large part of the northern hemisphere has quaternary deposits consisting of glacial clayey till. The till...

Induced Polarization (IP) has gained a lot of attention in connection to airborne Time Domain Electromagnetic (ATEM) data for mapping subsurface chargeability together with conductivity. Accounting for IP in AEM can have two purposes, the first one is recovering the true conductivity section without paying much attention to the magnitude of the IP...

Recently, the interest in the induced polarization (IP) phenomenon in airborne time-domain electromagnetic (ATEM) data has increased considerably. IP may affect the ATEM data significantly and mask underlying geologic structures. To simulate 2D airborne IP data, a 2D finite-element forward-modeling algorithm has been developed with the dispersive c...

The Capacitively Coupled Resistivity (CCR) method determines the electrical resistivity and permittivity by analysing the spectra of magnitude and phase shift of the electrical impedance. The CCR is well suited for the application in cryospheric and periglacial areas, because these areas provide the required physical conditions and logistical advan...

An integrated geophysical survey has been conducted at the Tarragona’s Cathedral (Catalonia, NE Spain) with the aim to confirm the potential occurrence of archaeological remains of the Roman Temple dedicated to the Emperor Augustus. Many hypotheses have been proposed about its possible location, the last ones regarding the inner part of the Cathedr...

Contaminant mass discharge is a commonly applied tool to evaluate the environmental impact of contaminated sites on water resources. At large contaminated sites with heterogeneous sources, such as landfills, the number of wells available is often not sufficient, leading to a high uncertainty of mass discharge estimates. In this study, we tackle the...

Accurate modelling of the conductivity structure of mineralizations can often be difficult. In order to remedy this, a parametric approach is often used. We have developed a parametric thin sheet code, with variable overburden. The code is capable of performing inversions of time‐domain airborne electromagnetic data, and it has been tested successf...

The application of airborne electromagnetic induced polarization (AEMIP) is increasing with the advances in airborne electromagnetic methods. In AEMIP, the Cole-Cole model is often applied for parameterization of the IP effect, however, the model parameters are known to be correlated in the inversion. We test the Maximum Phase Angle (MPA) Cole-Cole...

The application of time-domain induced polarization (TDIP) is increasing with advances in acquisition techniques, data processing and spectral inversion schemes. An inversion of TDIP data for the spectral Cole–Cole parameters is a non-linear problem, but by applying a 1-D Markov Chain Monte Carlo (MCMC) inversion algorithm, a full non-linear uncert...

An investigation of geological conditions is always a key point for planning infrastructure constructions. Bedrock surface and rock quality must be estimated carefully in the designing process of infrastructures. A large direct‐current resistivity and time‐domain induced‐polarization survey has been performed in Dalby, Lund Municipality, southern S...

The principle of equivalence is known to cause nonuniqueness in interpretations of direct current (DC) resistivity data. Low-or high-resistivity equivalences arise when a thin geologic layer with a low/high resistivity is embedded in a relative high-/low-resistivity background formation causing strong resistivity-thickness correlations. The equival...

Surface nuclear magnetic resonance is a geophysical technique providing non-invasive aquifer characterization. Two approaches are commonly used to invert surface nuclear magnetic resonance data: (1) inversions involving many depth layers of fixed thickness and (2) few-layer inversions without predetermined layer thicknesses. The advantage of the ma...

We have developed a synthetic multiparametric modeling and inversion exercise undertaken to study the robustness of inverting airborne time-domain electromagnetic (TDEM) data to extract Cole-Cole parameters. The following issues were addressed: nonuniqueness, ill posedness, dependency on manual processing and the effect of constraints, and a priori...

Time-domain induced polarisation and magnetic data were acquired to map and characterise the decommissioned and un-engineered municipal solid waste disposal site of the Kwame Nkrumah University of Science and Technology, located in the Kumasi Metropolis of Ghana. In this survey, 13 induced polarisation profiles 500-800 m long and 26 magnetic profil...

Leaching of organic and inorganic contamination from landfills is a serious environmental problem as surface water and aquifers are affected. In order to assess these risks and investigate the migration of leachate from the landfill, 2D and large scale 3D Electrical resistivity tomography were used at a heavily contaminated landfill in Grindsted, D...

Airborne electromagnetic (AEM) data is used throughout the world for mapping of mineral targets and groundwater resources. The development of technology and inversion algorithms has been tremendously over the last decade and results from these surveys are high-resolution images of the subsurface. In this keynote talk, we discuss an effective inver...

Characterization of varying bedrock properties is a common need in various contexts, ranging from large infrastructure pre-investigations to environmental protection. A direct current resistivity and time domain induced polarization (IP) survey aiming to characterize properties of a Cretaceous limestone was carried out in the Kristianstad basin, Sw...

The extraction of spectral information in the inversion process of time-domain (TD) induced polarization (IP) data is changing the use of the TDIP method. Data interpretation is evolving from a qualitative description of the subsurface, able only to discriminate the presence of contrasts in chargeability parameters, towards a quantitative analysis...

In the present study, we have used 3D ERT for detailed mapping of a polluted site at a challenging river site in the southern part of the Denmark. The survey layout involves several crossings of the meander of a river where a leachate plume from an old chemical factory site is expected to reach the river. Both resistivity and time domain induced po...

The extraction of spectral information in the inversion process of time-domain (TD) induced polarization (IP) data is changing the use of the TDIP method. Data interpretation is evolving from a qualitative description of the subsurface, able only to discriminate the presence of contrasts in chargeability parameters, towards a quantitative analysis...

Surface nuclear magnetic resonance technique, also called magnetic resonance sounding (MRS), is an emerging geophysical method that can detect the presence and spatial variations of the subsurface water content directly. In this paper, we introduce the MRS central loop geometry, in which the receiver loop is smaller than the transmitter loop and pl...

SUMMARY While the forefront of AEM research is focusing on the challenges of 3D modelling, the wide AEM community still rely on less sophisticated computational techniques for their calculations. Inversion of large time domain AEM surveys still prove a computational challenge within a 1D formulation, and require much more computational resources th...

SUMMARY We present a new algorithm for quasi-3D inversion of airborne transient electromagnetic data (AEM). The algorithm uses a 3D voxel grid for the model domain while the forward response and derivatives are calculated using interpolated "virtual" 1D models collocated at the AEM measurement points. The algorithm efficiently decouples the model d...

A recent airborne TEM survey in the Machile–Zambezi Basin of south western Zambia revealed high electrical resistivity anomalies (around 100 Ωm) in a low electrical resistivity (below 13 Ωm) background. The near surface (0–40 m depth range) electrical resistivity distribution of these anomalies appeared to be coincident with super- ficial features...

With permafrost thawing and changes in active layer dynamics induced by climate change, interactions between biogeochemical and thermal processes in the ground are of great importance. Here, active layer dynamics have been monitored using direct current (DC) resistivity and induced polarization (IP) measurements at high temporal resolution and at a...

A DCIP survey with different timing settings, electrode arrays, cable spreads and waveforms (50% and 100% duty cycle waveform) were carried out over the Liikavaara deposit in northern Sweden. All the measured data were inverted using AarhusInv. Measured data with 100% duty cycle waveform, which is much faster than the conventional 50% duty cycle wa...

3D surveying of resistivity and induced polarization has often utilized only a small number of electrodes determined by the number of addresses in the instrument. This is often in the range of 64-128 electrodes if mounted using a switching unit. Here we use a flexible and expandable 3D system that allows for arbitrary use of any set of parallel cab...

We have developed a new robust concept for the calculation of the depth of investigation (DOI) for inversion problems described by several intrinsic parameters, like the spectral inversion of time-domain induced polarization data or the inversion of full-decay Nuclear Magnetic Resonance soundings. A calculation of the DOI is crucial for interpretin...

electrical behaviour of DNAPLs during biodegradiation and weathering. We therefore used a TD SIP inversion to retrieve the Cole-Cole relaxation model for a detailed interpretation and a comparison to standard chargeability inversion results. While resistivity and chargeability results are good comparable the additional parameters τ and C seem promi...

The use of a specific inversion code, able to recover Cole Cole parameters, allowed us to extract chargeability info and improved resistivity estimation, from AEM dataset. Two case studies coming from Canada, for mining exploration, are presented: VTEM and HeliTEM data were re-processed, allowing the modeling of chargeability, confirmed by borehole...

One of the main limiting factors to the accuracy of large scale groundwater models is the scarcity of hydraulic data. High-resolution Airborne Electromagnetic Methods (AEM) are capable of mapping the electrical resistivity structure of the subsurface in great detail and covering large areas in short time and on a limited budget. As such, there is g...

Combined resistivity and time-domain direct current induced polarization (DCIP) measurements are traditionally carried out with a 50% duty cycle current waveform, taking the resistivity measurements during the on-time and the IP measurements during the off-time. One drawback with this method is that only half of the acquisition time is available fo...

The duration of time domain (TD) induced polarization (IP) current injections has significant impact on the acquired IP data as well as on the inversion models, if the standard evaluation procedure is followed. However, it is still possible to retrieve similar inversion models if the waveform of the injected current and the IP response waveform are...

Resistivity and induced polarization (IP) measurements on soil contaminated with non-aqueous phase liquids (NAPLs) show a great variety in results in previous research. Several laboratory studies have suggested that the presence of NAPLs in soil samples generally decrease the magnitude of the IP-effect, while others have indicated the opposite. A n...

Aarhus Geophysics (Дания), сов-местно с университетом Архуса и при поддержке научно-исследователь-ской лаборатории CSIRO (Австралия), позволили разработать эффективную методологию извлечения в ряде слу-чаев некоторых ВП параметров из аэро ЭМ данных, полученных методом ста-новления поля (TDEM). Ниже приведе-ны теоретические исследования этого явлени...

Surface NMR, also called magnetic resonance sounding (MRS) for 1D applications, has emerged as a promising geophysical method that is used to assess aquifer properties. A typical coincident-loop MRS measurement consists of a large wire loop deployed on the surface, acting as both a transmitter and a receiver. In this study, we present central-loop...

Contamination of potable groundwater by leaking CO2 is a potential risk of carbon sequestration. With the help of a field experiment, we investigated whether surface monitoring of direct current (DC) electric resistivity and induced polarization (IP) could detect geochemical changes induced by CO2 in a shallow aquifer. For this purpose, we injected...

Time‐domain electromagnetic data are conveniently inverted by using smoothly varying 1D models with fixed vertical discretization. The vertical smoothness of the obtained models stems from the application of Occam‐type regularization constraints, which are meant to address the ill‐posedness of the problem. An important side effect of such regulariz...

Environmental pollution from solid waste landfilling is a serious risk for groundwater and downstream surface water, especially when landfilling is carried out unengineered, with no protective layer underneath the waste deposits. Most research in Ghana and in other developing countries on unengineered landfills depend almost exclusively on hydroche...

Resistivity and time domain IP measurements using a 100% duty cycle square waveform current injection signal, and measuring the IP responses during current transmission, was modelled numerically and tested in the field against a traditional IP current injection with a 50% duty cycle waveform and measuring during the current off-time. The results sh...

Soils beneath former dry cleaning sites are often contaminated with the chlorinated hydrocarbons PCE and its degradation products, which are highly toxic and cancerogenic. In this study, resistivity and time domain induced polarization (DCIP) were measured at a former dry cleaning site in order to investigate if the source contamination of PCE coul...

We present an overview of a mature, robust and general algorithm providing a single framework for the inversion of most electromagnetic and electrical data types and instrument geometries. The implementation mainly uses a 1D earth formulation for electromagnetics and magnetic resonance sounding (MRS) responses, while the geoelectric responses are b...

Contamination of groundwater by leaking CO2 is a potential risk of carbon sequestration. With the help of a field experiment in western Denmark, we investigate to what extent surface electrical resistivity tomography (ERT) can detect and image dissolved CO2 in a shallow aquifer. For this purpose, we injected CO2 at a depth of 5 and 10 m and monitor...

The possibility of extracting IP information from AEM data never stopped being of interest to the scientific community and industry. Synthetic studies on AEM data (SkyTEM and VTEM) for simple Cole Cole models over layered earth confirm that some of the Cole cole parameters can, in favourable conditions, be recovered from AEM data. They also provide...

We present a focusing regularization technique utilizing a multi-layer model with fixed vertical discretization, while preserving the capability to reproduce sharp vertical transitions. The method relies on minimizing the number of layers of non-negligible resistivity gradient, instead of minimizing the norm of the model variation itself. AEM meth...

Increasingly, ground-based and airborne geophysical data sets are used to inform groundwater models. Recent research focuses on establishing coupling relationships between geophysical and groundwater parameters. To fully exploit such information, this paper presents and compares different hydrogeophysical inversion approaches to inform a field-scal...

This paper presents a new non-invasive methodology useful to univocally identify 3D rigid and elastic objects, particularly lapideous and ceramic artefacts and stones, by means of retrieving their capabilities to vibrate when stressed by artificial sources. A new instrument has been arranged to apply the methodology to large pieces in situ; it is p...

We present sharp reconstruction of multi-layer models using a spatially constrained inversion with minimum gradient support regularization. In particular, its application to airborne electromagnetic data is discussed. Airborne surveys produce extremely large datasets, traditionally inverted by using smoothly varying 1D models. Smoothness is a resul...

We present a comparison between two different regularisation schemes for multi-layer inversion of the MRS data. The two regularizations consist of the norm (Occam’s inversion) and the support (focused inversion) of the variation of the water content and relaxation time. The focused regularization provides a sharp inversion as it minimizes the area...

We present a geophysical inversion algorithm working directly in a voxel grid disconnected from the actual measuring points, which allows for straightforward integration of different data types in joint inversion, for informing geological/hydrogeological models directly and for easier incorporation of prior information. Inversion of geophysical dat...

Contamination of potable groundwater by leaking CO2 is a potential risk of carbon sequestration. With the help of a field experiment, we investigate if surface electrical resistivity tomography (ERT) can detect dissolved CO2 in a shallow aquifer. For this purpose, we injected CO2 at a depth of 5 and 10 m and monitored its migration using 320 surfac...

The Time Domain Induced Polarization (TDIP) technique is widely used in applied geophysics, particularly for environmental issues, for instance for delineating landfills or detecting leachate percolation. Because the reliability of IP data remains an issue at the field scale, this paper deals with the factors controlling data quality and compares d...

Increasingly, ground-based and airborne geophysical data sets are used to inform groundwater models. Recent research focuses on establishing coupling relationships between geophysical and groundwater parameters. To fully exploit such information, this paper presents and compares different hydrogeophysical inversion approaches to inform a field-scal...

We present an extension of the spatially constrained inversion (SCI) that facilitates sharp boundary inversions on multi-layer models by using a Minimum Gradient Support (MGS) stabilizer. Airborne surveys produce extremely large datasets that are traditionally inverted by using smoothly varying 1D multi-layer models. Smoothness is a result of the...

Field-based time domain (TD) induced polarization (IP) surveys are usually modelled by taking into account only the integral chargeability, thus disregarding spectral content. Furthermore, the effect of the transmitted waveform is commonly neglected, biasing inversion results. Given these limitations of conventional approaches, a new 2-D inversion...

This study uses time-domain induced polarization data for the delineation and characterization of the former landfill site at Eskelund, Denmark. With optimized acquisition parameters combined with a new inversion algorithm, we use the full content of the decay curve and retrieve spectral information from time-domain IP data. Thirteen IP/DC profiles...

In a sedimentary environment, quasi-layered models often represent the actual geology more accurately than smooth minimum-structure models. We have developed a new layered and laterally constrained inversion algorithm for time domain induced polarization data. The algorithm is based on the time transform of a complex resistivity forward response an...

We present a new scheme for joint and laterally constrained inversion (LCI) of magnetic resonance sounding (MRS) data and transient electromagnetic (TEM) data, which greatly improves the estimation of the MRS model parameters. MRS is a non-invasive geophysical technique which directly quantifies the water content distribution from surface measureme...

We present a new, efficient and accurate forward modelling and inversion scheme for magnetic resonance sounding (MRS) data. MRS, also called surface-nuclear magnetic resonance (surface-NMR), is the only non-invasive geophysical technique that directly detects free water in the subsurface. Based on the physical principle of NMR, protons of the water...

We developed a new scheme for joint and laterally constrained inversion (LCI) of magnetic resonance sounding (MRS) data and transient electromagnetic (TEM) data, which greatly improves the estimation of the MRS model parameters. During the last few decades, electrical and electromagnetic methods have been widely used for groundwater investigation,...

A direct current (DC) resistivity and time domain induced polarization (TDIP) survey was undertaken at a decommissioned landfill site situated in Hørløkke, Denmark, for the purpose of mapping the waste deposits and to discriminate important geological units that control the hydrology of the surrounding area. It is known that both waste deposits and...

Time-domain-induced polarization has significantly broadened its field of reference during the last decade, from mineral exploration to environmental geophysics, e.g., for clay and peat identification and landfill characterization. Though, insufficient modeling tools have hitherto limited the use of time-domain-induced polarization for wider purpos...

A DC resistivity (DC) and Time Domain Induced Polarization (TDIP) survey was undertaken at a decommissioned landfill site situated in Hørløkke, Denmark, for the purpose of mapping the waste deposits and to discriminate important geological units that control the hydrology of the surrounding area. It is known that both waste deposits and clay have c...

In this study we present a joint inversion of Magnetic resonance Sounding (MRS) and time domain electromagnetic (TEM) data. The joint scheme offers a better resolution of the model parameters than a traditional independent inversion of MRS and TEM. MRS is a non-invasive geophysical technique applied to groundwater investigations. The method offers...

In the computation of the forward response for Time Domain Induced Polarization the incomplete description of the transmitter waveform causes dramatic errors in the estimation of the magnitude and time characteristic of the IP phenomenon. In fact both the duration of the current pulse and the sequence of pulses used for the stacking procedure have...

We have developed a new, robust 2D inversion approach for modelling time domain induced potential data. Instead of considering the integral chargeability, the full IP waveform is modelled allowing inversion for spectral content in terms of the Cole-Cole parameters. The method is based on a finite element complex resistivity forward response, which...

The Magnetic Resonance Sounding (MRS) method, also known as surface NMR, is a non-invasive geophysical method which directly studies groundwater reservoirs from surface measurements. It is capable of direct estimating of water content distribution (from initial amplitudes) and indirect information on pore sizes (from relaxation time). The purpose o...