Electrical resistivity tomography (ERT) and induced polarization (IP) methods are now widely used in many interdisciplinary projects. Although field surveys using these methods are relatively ...straightforward, ERT and IP data require the application of inverse methods prior to any interpretation. Several established non-commercial inversion codes exist, but they typically require advanced knowledge to use effectively. ResIPy was developed to provide a more intuitive, user-friendly, approach to inversion of geoelectrical data, using an open source graphical user interface (GUI) and a Python application programming interface (API). ResIPy utilizes the mature R2/cR2 inversion codes for ERT and IP, respectively. The ResIPy GUI facilitates data importing, data filtering, error modeling, mesh generation, data inversion and plotting of inverse models. Furthermore, the easy to use design of ResIPy and the help provided inside makes it an effective educational tool. This paper highlights the rationale and structure behind the interface, before demonstrating its capabilities in a range of environmental problems. Specifically, we demonstrate the ease at which ResIPy deals with topography, advanced data processing, the ability to fix and constrain regions of known geoelectrical properties, time-lapse analysis and the capability for forward modeling and survey design.
•Geophysics is more frequently used in interdisciplinary projects by non-specialists.•ResIPy is a simple to use, intuitive, open source graphical user interface and API.•ResIPy is a good teaching tool to learn how to invert and model geoelectrical data.•Data filtering and error modeling of resistivity and IP data improve inversion.•Field applications and survey design with ResIPy is demonstrated.
Introduction Characterization of the shallow subsurface in mountain catchments is important for understanding hydrological processes and soil formation. The depth to the soil/bedrock interface (e.g., ...the upper ~5 m) is of particular interest. Frequency domain electromagnetic induction (FDEM) methods are well suited for high productivity characterization for this target as they have short acquisition times and do not require direct coupling with the ground. Although traditionally used for revealing lateral electrical conductivity (EC) patterns, e.g., to produce maps of salinity or water content, FDEM inversion is increasingly used to produce depth-specific models of EC. These quantitative models can be used to inform several depth-specific properties relevant to hydrological modeling (e.g. depths to interfaces and soil water content). Material and methods There are a number of commercial FDEM instruments available; this work compares a multi-coil device (i.e., a single-frequency device with multiple receiver coils) and a multi-frequency device (i.e., a single receiver device with multiple frequencies) using the open-source software EMagPy. Firstly, the performance of both devices is assessed using synthetic modeling. Secondly, the analysis is applied to field data from an alpine catchment. Results Both instruments retrieved a similar EC model in the synthetic and field cases. However, the multi-frequency instrument displayed shallower sensitivity patterns when operated above electrically conductive grounds (i.e., 150 mS/m) and therefore had a lower depth of investigation. From synthetic modeling, it also appears that the model convergence for the multi-frequency instrument is more sensitive to noise than the multi-coil instrument. Conclusion Despite these limitations, the multi-frequency instrument is smaller and more portable; consequently, it is easier to deploy in mountainous catchments.
Frequency domain electromagnetic induction (EMI) methods have had a long history of qualitative mapping for environmental applications. More recently, the development of multi-coil and ...multi-frequency instruments is such that the focus has shifted toward inverting data to obtain quantitative models of electrical conductivity. However, whilst the collection of EMI data is relatively straightforward, inverse modeling is more complicated. Furthermore, although several commercial and open-source inversion codes exist, there is still a need for user-friendly software that can bring EMI inversion to a non-specialist audience. Here the open-source EMagPy software is presented as an intuitive approach to modeling EMI data. It comprises a graphical user interface (GUI) and a Python application programming interface (API) that is more suitable for specialized tasks. EMagPy implements both cumulative sensitivity and Maxwell-based forward operators and can model data for 1D and quasi-2D/3D cases using either deterministic or probabilistic methods. The EMagPy GUI has a logical ‘tab-based’ layout to lead the user through data importing, data filtering, inversion, and plotting of raw and inverted data. Additionally, a dedicated forward modeling tab is presented that allows the generation of synthetic data. In this publication, necessary considerations, and background, of EMI theory are described before EMagPy's capabilities are presented through a series of synthetic and field-based case studies. Firstly, the performance of cumulative sensitivity and Maxwell-based forward models, and the influence of measurement noise are assessed for synthetic cases. Then the importance of data calibration for a riparian wetland dataset, the ability to include a priori information for a river-borne survey, and the potential for monitoring soil moisture in a time-lapse example are all investigated. It is anticipated that EMagPy offers a user-friendly tool suitable for novice and experienced practitioners alike, and its intuitive nature means it can provide a useful tool for teaching purposes.
•EMagPy is an open-source Python API and GUI for 1D EMI modeling/inversion.•Both Maxwell-based and cumulative sensitivity forward models are implemented.•Inversion algorithms include deterministic and probabilistic methods.•The cumulative sensitivity function of McNeill (1980) performs well in low EC environments.•Capabilities of EMagPy are shown through case studies with real and synthetic data.
Understanding ecologically sensitive wetlands often requires non‐invasive methods to characterize their complex structure (e.g., deposit heterogeneity) and hydrogeological parameters (e.g., porosity ...and hydraulic conductivity). Here, electrical conductivities of a riparian wetland were obtained using frequency domain electromagnetic induction (EMI) methods. The wetland was previously characterized by extensive intrusive measurements and 3D electrical resistivity tomography (ERT) surveys and hence offers an ideal opportunity to objectively assess EMI methods. Firstly, approaches to obtain structural information (e.g., elevation and thickness of alluvium) from EMI data and inverted models were assessed. Regularized and sharp inversion algorithms were investigated for ERT calibrated EMI data. Moreover, the importance of EMI errors in inversion was investigated. The hydrological information content was assessed using correlations with piezometric data and petrophysical models. It was found that EMI data were dominated by the thickness of peaty alluvial soils and relatively insensitive to topography and total alluvial thickness. Furthermore, although error weighting in the inversion improved the accuracy of alluvial soil thickness predictions, the multi‐linear regression method performed the best. For instance, an iso‐conductivity method to estimate the alluvial soil thickness in the regularized models had a normalized mean absolute difference (NMAD) of 21.4%, and although this performed better than the sharp inversion algorithm (NMAD = 65.3%), the multi‐linear regression approach (using 100 intrusive observations) achieved a NMAD = 18.0%. In terms of hydrological information content, correlations between EMI results and piezometric data were poor, however robust relationships between petrophysically derived porosity and hydraulic conductivity were observed for the alluvial soils and gravels.
Key Points
Raw ECa values are highly correlated with the thickness of alluvial soil in a riparian wetland
Alluvial soil thickness predictions from multi‐linear regressions were more accurate than from electromagnetic induction (EMI) inversion methods
Robust predictions of hydraulic conductivity across the field site require more extensive intrusive data
Permafrost is a widespread phenomenon in the cold regions of the globe and is under‐represented in global monitoring networks. This study presents a novel low‐cost, low‐power, and robust Autonomous ...Electrical Resistivity Tomography (A‐ERT) monitoring system and open‐source processing tools for permafrost monitoring. The processing workflow incorporates diagnostic and filtering tools and utilizes open‐source software, ResIPy, for data inversion. The workflow facilitates quick and efficient extraction of key information from large data sets. Field experiments conducted in Antarctica demonstrated the system's capability to operate in harsh and remote environments and provided high‐temporal‐resolution imaging of ground freezing and thawing dynamics. This data set and processing workflow allow for a detailed investigation of how meteorological conditions impact subsurface processes. The A‐ERT setup can complement existing monitoring networks on permafrost and is suitable for continuous monitoring in polar and mountainous regions, contributing to cryosphere research and gaining deeper insights into permafrost and active layer dynamics.
Plain Language Summary
Permafrost, frozen ground in cold regions, has significant impacts on the global environment. Monitoring of permafrost is crucial because it influences the global carbon cycle, hydrology, contaminant movement, and ecosystem stability. However, current monitoring systems have limitations, particularly in remote regions like Antarctica. To tackle this challenge, a new monitoring system, Autonomous Electrical Resistivity Tomography (A‐ERT), was introduced. A‐ERT is a geophysical technique that employs electrical signals to study ground freezes and thaws with high precision over time. Alongside this, open‐source processing tools were developed to process obtained A‐ERT data and efficiently extract essential information from large data sets. The developed A‐ERT system is robust, low‐cost, low‐power, and designed to operate in harsh conditions. Tested in Antarctica, our findings show that A‐ERT data combined with processing pipelines offers a valuable tool for examining freezing and thawing processes in extreme environments. The proposed setup can contribute to a network of autonomous permafrost monitoring systems, important for cryosphere research and advancing our understanding of climate change's impact on permafrost dynamics.
Key Points
We present a robust low‐cost Autonomous Electrical Resistivity Tomography system for permafrost monitoring in polar and mountainous regions
We introduce an open‐source tool for processing and inverting large data sets, enabling quick and efficient extraction of key information
Field experiments conducted in Antarctica show high‐temporal‐resolution imaging of ground freezing and thawing dynamics
Police use of force bears on central matters of political science, including equality of citizen treatment by government. In light of recent high-profile officer-involved shootings (OIS) that ...resulted in civilian deaths, we assess whether, conditional on a shooting, a civilian’s race predicts fatality during police-civilian interactions. We combine Los Angeles data on OIS with a novel research design to estimate the causal effects of fatal shootings on citizen-initiated contact with government. Specifically, we examine whether fatal OIS affect citizen contact with the municipal government via use of the emergency 911 and nonemergency 311 call systems in Los Angeles. We find no average effect of OIS on patterns of 911 and 311 call behavior across a wide range of empirical specifications. Our results suggest, contrary to existing evidence, that OIS, in and of themselves, do not substantively change civic behavior, at least not citizen-initiated contact with local government.
To constrain the closure time of the Paleo-Asian Ocean and better understand the movement processes of different terranes in the Northern Xinjiang region, we present a combined geochronologic and ...paleomagnetic study of Carboniferous andesite and limestones from the Yamansu and Dikaner Formations in the Aqishan–Yamansu Belt (AYB). Zircon UPb dating of the Dikaner Formation andesite yielded an age of 313.2 ± 2.0 Ma, and the zircon εHf(t) values ranged from −15.6 to 16.3. Stepwise thermal demagnetization successfully isolated a lower temperature component (LTC) and a stable higher temperature component (HTC) from 18 limestone beds. The LTC represents a viscous remanent magnetization of the present geomagnetic field. In comparison, the HTC is interpreted to represent Late Carboniferous magnetization, generating two paleopoles at 84.6°N, 38.3°E (A95 = 11.6°) for ~313 Ma and 77.2°N, 301.5°E (A95 = 5.5°) for 321–318 Ma. These results show that the AYB moved northward from 30.5 ± 6.5°N to 44.8 ± 8.3°N during the interval between 321–318 Ma and ~ 313 Ma. Compared to other published coeval paleomagnetic poles from surrounding blocks, it can be concluded that the western Paleo-Asian Ocean (between Tarim and Siberia) had been closed since the Late Carboniferous. In contrast, the eastern Paleo-Asian Ocean (between Siberia and Dunhuang-Alxa-NCB) was still open during this time. Besides, the counterclockwise rotations of AYB with respect to Siberia-Mongolia-Tuva and Tarim are estimated to be 88.5° ± 14.1° and 46.5° ± 13.4° since ~313 Ma respectively. Combined with other geological evidence, we propose that Yili-Junggar-Turpan-Hami-AYB had to move eastward to the still open eastern Paleo-Asian Ocean to accommodate the compressive tectonic stress field during the Late Carboniferous, and a Late Carboniferous tectono-paleogeography of the Paleo-Asian Ocean has been reconstructed.
•New reliable C2 paleomagnetic poles of the Aqishan–Yamansu belt (AYB) were obtained.•The AYB moved northward from 30.5 ± 6.5°N to 44.8 ± 8.3°N between 321–318 Ma to ~313 Ma.•The western Paleo-Asian ocean (between Tarim and Siberia) had been closed since C2.•The CCW rotations of AYB were identified with respect to Siberia and Tarim since C2.
The groundwater-surface water (GW-SW) interface has received interest due to its active role in governing GW-SW exchanges, and its implications for environmental health at reach to catchment scales. ...This thesis advances geophysical methods for characterising the GW-SW interface; in addition it has broader implications for general hydrogeophysics. Three key areas are explored: (1) electromagnetic induction (EMI) characterisation of a riparian wetland, (2) field and laboratory induced polarisation (IP) methods to assess biogeochemical properties of a riverbed, and (3) timelapse electrical resistivity imaging (ERI) monitoring of a river and neighbouring riparian zone. Advances in EMI instruments and inversion methods are such that there is interest in using EMI to obtain electrical conductivity models. The ability of EMI methods to resolve hydrogeological properties is assessed here. An inversion algorithm was developed to obtain models of sharply, and smoothly, varying conductivity. It was demonstrated that data collected at 1 m elevation ought to be inverted using a Maxwell based forward model, as opposed to a cumulative sensitivity forward model. Additionally, it was found that measurement noise has more influence on the convergence of inversions for data collected at greater elevations. In comparison, raw EMI data were used to resolve peat depth of the wetland (RMSE=18%) and correlated well with peat hydraulic conductivity (R2 =0.8). These findings demonstrate that in many cases use of inversion methods is unnecessary; this also simplifies data collection as calibration of EMI data is therefore unimportant. Links between induced polarisation (IP) and hydrologically/biogeochemically relevant properties have been shown in the laboratory. In this work, riverbed sediments are characterised using lab and field based IP methods, and measurements of grain size, cation exchange capacity and surface area. Contrasts of riverbed sediments could be resolved using lab IP; additionally, relationships to surface area matched published studies. Electrical contrasts were more significant at frequencies higher than those typically used in the field; this indicates the benefit of using multi-frequency field IP devices. It was not possible to resolve electrical contrasts with the field data because of complications, such as erroneous fixing of river resistivity and the influence of micro-topography. This work highlights the necessity of forward modelling to confirm results of aquatic ERI surveys. Time-lapse ERI was used to resolve GW-SW exchanges on a GW dependent Chalk river. Correlation analysis was used to identify areas of the subsurface that exhibited similar hydrological patterns. Despite development of an inversion workflow to account for a changing stage, resistivity patterns in the riverbed were too extreme to be attributed to dynamics in the riverbed and were attributed to inversion artefacts. It was, however, possible to reveal the complex interplay of changing GW levels, biological activity, precipitation and vegetation cutting, and its influence on the riparian zone. This study highlighted how correlation statistics could be used to summarise large ERI data sets and reveal complex patterns and improve conceptual understanding of site hydrology.
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