TY - JOUR A1 - Guillemoteau, Julien A1 - Simon, Francois-Xavier A1 - Hulin, Guillaume A1 - Dousteyssier, Bertrand A1 - Dacko, Marion A1 - Tronicke, Jens T1 - 3-D imaging of subsurface magnetic permeability/susceptibility with portable frequency domain electromagnetic sensors for near surface exploration JF - Geophysical journal international N2 - The in-phase response collected by portable loop-loop electromagnetic induction (EMI) sensors operating at low and moderate induction numbers (<= 1) is typically used for sensing the magnetic permeability (or susceptibility) of the subsurface. This is due to the fact that the in-phase response contains a small induction fraction and a preponderant induced magnetization fraction. The magnetization fraction follows the magneto-static equations similarly to the magnetic method but with an active magnetic source. The use of an active source offers the possibility to collect data with several loop-loop configurations, which illuminate the subsurface with different sensitivity patterns. Such multiconfiguration soundings thereby allows the imaging of subsurface magnetic permeability/susceptibility variations through an inversion procedure. This method is not affected by the remnant magnetization and theoretically overcomes the classical depth ambiguity generally encountered with passive geomagnetic data. To invert multiconfiguration in-phase data sets, we propose a novel methodology based on a full-grid 3-D multichannel deconvolution (MCD) procedure. This method allows us to invert large data sets (e.g. consisting of more than a hundred thousand of data points) for a dense voxel-based 3-D model of magnetic susceptibility subject to smoothness constraints. In this study, we first present and discuss synthetic examples of our imaging procedure, which aim at simulating realistic conditions. Finally, we demonstrate the applicability of our method to field data collected across an archaeological site in Auvergne (France) to image the foundations of a Gallo-Roman villa built with basalt rock material. Our synthetic and field data examples demonstrate the potential of the proposed inversion procedure offering new and complementary ways to interpret data sets collected with modern EMI instruments. KW - Magnetic properties KW - Controlled source electromagnetics (CSEM) KW - Electromagnetic theory KW - Environmental magnetism KW - Inverse theory Y1 - 2019 U6 - https://doi.org/10.1093/gji/ggz382 SN - 0956-540X SN - 1365-246X VL - 219 IS - 3 SP - 1773 EP - 1785 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Allroggen, Niklas Robin A1 - Booth, Adam D. A1 - Baker, Sandra E. A1 - Ellwood, Stephen A. A1 - Tronicke, Jens T1 - High-resolution imaging and monitoring of animal tunnels using 3D ground-penetrating radar JF - Near surface geophysics N2 - Ground-penetrating radar is widely used to provide highly resolved images of subsurface sedimentary structures, with implications for processes active in the vadose zone. Frequently overlooked among these structures are tunnels excavated by fossorial animals (e.g., moles). We present two repeated ground-penetrating radar surveys performed a year apart in 2016 and 2017. Careful three-dimensional data processing reveals, in each data set, a pattern of elongated structures that are interpreted as a subsurface mole tunnel network. Our data demonstrate the ability of three-dimensional ground-penetrating radar imaging to non-invasively delineate the small animal tunnels (similar to 5 cm diameter) at a higher spatial and geolocation resolution than has previously been achieved. In turn, this makes repeated surveys and, therefore, long-term monitoring possible. Our results offer valuable insight into the understanding of the near-surface and showcase a potential new application for a geophysical method as well as a non-invasive method of ecological surveying. KW - Ground-penetrating radar KW - Shallow subsurface KW - Environmental Y1 - 2019 U6 - https://doi.org/10.1002/nsg.12039 SN - 1569-4445 SN - 1873-0604 VL - 17 IS - 3 SP - 291 EP - 298 PB - Wiley CY - Hoboken ER - TY - GEN A1 - Hugenschmidt, Johannes A1 - Giannopoulos, Antonios A1 - Tronicke, Jens T1 - Foreword T2 - Near surface geophysics Y1 - 2019 U6 - https://doi.org/10.1002/nsg.12050 SN - 1569-4445 SN - 1873-0604 VL - 17 IS - 3 SP - 199 EP - 200 PB - Wiley CY - Oxford ER - TY - JOUR A1 - Klose, Tim A1 - Guillemoteau, Julien A1 - Simon, Francois-Xavier A1 - Tronicke, Jens T1 - Toward subsurface magnetic permeability imaging with electromagnetic induction sensors BT - Sensitivity computation and reconstruction of measured data JF - Geophysics N2 - In near-surface geophysics, small portable loop-loop electro-magnetic induction (EMI) sensors using harmonic sources with a constant and rather small frequency are increasingly used to investigate the electrical properties of the subsurface. For such sensors, the influence of electrical conductivity and magnetic permeability on the EMI response is well-understood. Typically, data analysis focuses on reconstructing an electrical conductivity model by inverting the out-of-phase response. However, in a variety of near-surface applications, magnetic permeability (or susceptibility) models derived from the in-phase (IP) response may provide important additional information. In view of developing a fast 3D inversion procedure of the IP response for a dense grid of measurement points, we first analyze the 3D sensitivity functions associated with a homogeneous permeable half-space. Then, we compare synthetic data computed using a linear forward-modeling method based on these sensitivity functions with synthetic data computed using full nonlinear forward-modeling methods. The results indicate the correctness and applicability of our linear forward-modeling approach. Furthermore, we determine the advantages of converting IP data into apparent permeability, which, for example, allows us to extend the applicability of the linear forward-modeling method to high-magnetic environments. Finally, we compute synthetic data with the linear theory for a model consisting of a controlled magnetic target and compare the results with field data collected with a four-configuration loop-loop EMI sensor. With this field-scale experiment, we determine that our linear forward-modeling approach can reproduce measured data with sufficiently small error, and, thus, it represents the basis for developing efficient inversion approaches. KW - Electromagnetics KW - Imaging KW - Magnetic+Susceptibility KW - Near+Surface KW - Modeling Y1 - 2018 U6 - https://doi.org/10.1190/GEO2017-0827.1 SN - 0016-8033 SN - 1942-2156 VL - 83 IS - 5 SP - E335 EP - E345 PB - Society of Exploration Geophysicists CY - Tulsa ER - TY - JOUR A1 - Tronicke, Jens A1 - Trauth, Martin H. T1 - Classroom-sized geophysical experiments BT - magnetic surveying using modern smartphone devices JF - European Journal of Physics N2 - Modern mobile devices (i.e. smartphones and tablet computers) are widespread, everyday tools, which are equipped with a variety of sensors including three-axis magnetometers. Here, we investigate the feasibility and the potential of using such mobile devices to mimic geophysical experiments in the classroom in a table-top setup. We focus on magnetic surveying and present a basic setup of a table-top experiment for collecting three-component magnetic data across well-defined source bodies and structures. Our results demonstrate that the quality of the recorded data is sufficient to address a number of important basic concepts in the magnetic method. The shown examples cover the analysis of magnetic data recorded across different kinds of dipole sources, thus illustrating the complexity of magnetic anomalies. In addition, we analyze the horizontal resolution capabilities using a pair of dipole sources placed at different horizontal distances to each other. Furthermore, we demonstrate that magnetic data recorded with a mobile device can even be used to introduce filtering, transformation, and inversion approaches as they are typically used when processing magnetic data sets recorded for real-world field applications. Thus, we conclude that such table-top experiments represent an easy-to-implement experimental procedure (as student exercise or classroom demonstration) and can provide first hands-on experience in the basic principles of magnetic surveying including the fundamentals of data acquisition, analysis and processing, as well as data evaluation and interpretation. KW - geophysics KW - magnetic surveying KW - table-top experiment Y1 - 2018 U6 - https://doi.org/10.1088/1361-6404/aaad5b SN - 0143-0807 SN - 1361-6404 VL - 39 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Jackisch, Conrad A1 - Angermann, Lisa A1 - Allroggen, Niklas A1 - Sprenger, Matthias A1 - Blume, Theresa A1 - Tronicke, Jens A1 - Zehe, Erwin T1 - Form and function in hillslope hydrology BT - in situ imaging and characterization of flow-relevant structures T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The study deals with the identification and characterization of rapid subsurface flow structures through pedo- and geo-physical measurements and irrigation experiments at the point, plot and hillslope scale. Our investigation of flow-relevant structures and hydrological responses refers to the general interplay of form and function, respectively. To obtain a holistic picture of the subsurface, a large set of different laboratory, exploratory and experimental methods was used at the different scales. For exploration these methods included drilled soil core profiles, in situ measurements of infiltration capacity and saturated hydraulic conductivity, and laboratory analyses of soil water retention and saturated hydraulic conductivity. The irrigation experiments at the plot scale were monitored through a combination of dye tracer, salt tracer, soil moisture dynamics, and 3-D time-lapse ground penetrating radar (GPR) methods. At the hillslope scale the subsurface was explored by a 3-D GPR survey. A natural storm event and an irrigation experiment were monitored by a dense network of soil moisture observations and a cascade of 2-D time-lapse GPR "trenches". We show that the shift between activated and non-activated state of the flow paths is needed to distinguish structures from overall heterogeneity. Pedo-physical analyses of point-scale samples are the basis for sub-scale structure inference. At the plot and hillslope scale 3-D and 2-D time-lapse GPR applications are successfully employed as non-invasive means to image subsurface response patterns and to identify flow-relevant paths. Tracer recovery and soil water responses from irrigation experiments deliver a consistent estimate of response velocities. The combined observation of form and function under active conditions provides the means to localize and characterize the structures (this study) and the hydrological processes (companion study Angermann et al., 2017, this issue). T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 665 KW - Ground Penetrating Radar KW - preferential flow KW - solute transport KW - Catchment Hydrology KW - multiple scales KW - soil moisture KW - water content KW - tracer KW - field KW - model Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-419188 SN - 1866-8372 IS - 665 ER - TY - GEN A1 - Angermann, Lisa A1 - Jackisch, Conrad A1 - Allroggen, Niklas A1 - Sprenger, Matthias A1 - Zehe, Erwin A1 - Tronicke, Jens A1 - Weiler, Markus A1 - Blume, Theresa T1 - Form and function in hillslope hydrology BT - characterization of subsurface flow based on response observations T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The phrase form and function was established in architecture and biology and refers to the idea that form and functionality are closely correlated, influence each other, and co-evolve. We suggest transferring this idea to hydrological systems to separate and analyze their two main characteristics: their form, which is equivalent to the spatial structure and static properties, and their function, equivalent to internal responses and hydrological behavior. While this approach is not particularly new to hydrological field research, we want to employ this concept to explicitly pursue the question of what information is most advantageous to understand a hydrological system. We applied this concept to subsurface flow within a hillslope, with a methodological focus on function: we conducted observations during a natural storm event and followed this with a hillslope-scale irrigation experiment. The results are used to infer hydrological processes of the monitored system. Based on these findings, the explanatory power and conclusiveness of the data are discussed. The measurements included basic hydrological monitoring methods, like piezometers, soil moisture, and discharge measurements. These were accompanied by isotope sampling and a novel application of 2-D time-lapse GPR (ground-penetrating radar). The main finding regarding the processes in the hillslope was that preferential flow paths were established quickly, despite unsaturated conditions. These flow paths also caused a detectable signal in the catchment response following a natural rainfall event, showing that these processes are relevant also at the catchment scale. Thus, we conclude that response observations (dynamics and patterns, i.e., indicators of function) were well suited to describing processes at the observational scale. Especially the use of 2-D time-lapse GPR measurements, providing detailed subsurface response patterns, as well as the combination of stream-centered and hillslope-centered approaches, allowed us to link processes and put them in a larger context. Transfer to other scales beyond observational scale and generalizations, however, rely on the knowledge of structures (form) and remain speculative. The complementary approach with a methodological focus on form (i.e., structure exploration) is presented and discussed in the companion paper by Jackisch et al. (2017). T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 658 KW - ground-penetrating radar KW - preferential flow KW - water-flow KW - runoff generation KW - vadose zone KW - catchment KW - scale KW - tracer KW - time KW - pore Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-419161 SN - 1866-8372 IS - 658 ER - TY - JOUR A1 - Guillemoteau, Julien A1 - Lück, Erika A1 - Tronicke, Jens T1 - 1D inversion of direct current data acquired with a rolling electrode system JF - Journal of applied geophysics N2 - Direct current systems employing a kinematic surveying strategy allow to analyze the electrical resistivity of the subsurface for large areas (i.e., several hectares). Typical applications are found in precision agriculture, archaeological prospecting and soil sciences. With the typical survey setting, the collected data sets are often characterized by a rather high level of noise and a rather coarse lateral sampling compared to data acquired with fixed electrodes. We therefore present an efficient one-dimensional inversion approach in which we put special attention on modeling the effects of noise. We apply this method to data recorded with a five-offset equatorial dipole-dipole system employing rolling electrodes. By performing several synthetic tests with realistic noise levels, we found that the considered five-configuration soundings allow for a reliable imaging of two-layer cases in the uppermost two meters of the subsurface, where the subsurface can be assumed to follow a horizontally layered geometry within 3 m around the system. By analyzing the corresponding sensitivity functions, we also show that the equatorial dipole-dipole array is relatively well suited for a 1D inversion approach compared to standard in-line electrode arrays. To illustrate this aspect, we show that our method can provide results similar to those obtained with a 2D Wenner imaging procedure for data recorded across a well-constrained 2D target. We finally apply our method to a large five-offset data set acquired in an agricultural study. The final pseudo-3D model of electrical resistivity is in accordance with borehole data available for the surveyed area. Our results demonstrate the applicability and the versatility of the presented inversion approach for large-scale data sets as they are typically collected with such rolling electrode systems. (C) 2017 Elsevier B.V. All rights reserved. Y1 - 2017 U6 - https://doi.org/10.1016/j.jappgeo.2017.09.010 SN - 0926-9851 SN - 1879-1859 VL - 146 SP - 167 EP - 177 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Guillemoteau, Julien A1 - Christensen, Niels Boie A1 - Jacobsen, Bo Holm A1 - Tronicke, Jens T1 - Fast 3D multichannel deconvolution of electromagnetic induction loop-loop apparent conductivity data sets acquired at low induction numbers JF - Geophysics N2 - Electromagnetic induction (EMI) sensors using sufficiently low-frequency harmonic sources and sufficiently small loop separations operate in the low-induction-number (LIN) domain for a relatively wide range of background conductivity. These systems are used in diverse near-surface investigations including applications from soil sciences, hydrology, and archaeology. The special case of portable multiconfiguration EMI sensors operating at frequencies <= 20 kHz offers the possibility of using a fast linear deconvolution method to interpret multichannel data sets in three dimensions. Here, we have developed a fast 3D inversion/deconvolution method regularized with 3D smoothness constraints and formulated in the hybrid spectral-spatial domain. Compared with other linear approaches, the spectral-spatial domain formulation significantly reduces the computational cost of the processing and opens the door for real-time 3D interpretation of large data sets consisting of more than 100,000 data points. First, we test our proposed algorithm on synthetic data sets computed with the full Maxwell theory. Then, we apply our method to a real four-configuration EMI data set acquired to map the thickness of peat layers embedded in a sandy environment. For the synthetic and the field example, we compared our result with the result obtained using a standard point-by-point 1D nonlinear inversion approach. This comparison demonstrates that the proposed methodology provides superior lateral resolution compared with the 1D nonlinear inversion, at the same time significantly reducing the computational cost of the processing. Y1 - 2017 U6 - https://doi.org/10.1190/GEO2016-0518.1 SN - 0016-8033 SN - 1942-2156 VL - 82 SP - E357 EP - E369 PB - Society of Exploration Geophysicists CY - Tulsa ER - TY - JOUR A1 - Angermann, Lisa A1 - Jackisch, Conrad A1 - Allroggen, Niklas A1 - Sprenger, Matthias A1 - Zehe, Erwin A1 - Tronicke, Jens A1 - Weiler, Markus A1 - Blume, Theresa T1 - Form and function in hillslope hydrology: characterization of subsurface flow based on response observations JF - Hydrology and earth system sciences : HESS N2 - The phrase form and function was established in architecture and biology and refers to the idea that form and functionality are closely correlated, influence each other, and co-evolve. We suggest transferring this idea to hydrological systems to separate and analyze their two main characteristics: their form, which is equivalent to the spatial structure and static properties, and their function, equivalent to internal responses and hydrological behavior. While this approach is not particularly new to hydrological field research, we want to employ this concept to explicitly pursue the question of what information is most advantageous to understand a hydrological system. We applied this concept to subsurface flow within a hillslope, with a methodological focus on function: we conducted observations during a natural storm event and followed this with a hillslope-scale irrigation experiment. The results are used to infer hydrological processes of the monitored system. Based on these findings, the explanatory power and conclusiveness of the data are discussed. The measurements included basic hydrological monitoring methods, like piezometers, soil moisture, and discharge measurements. These were accompanied by isotope sampling and a novel application of 2-D time-lapse GPR (ground-penetrating radar). The main finding regarding the processes in the hillslope was that preferential flow paths were established quickly, despite unsaturated conditions. These flow paths also caused a detectable signal in the catchment response following a natural rainfall event, showing that these processes are relevant also at the catchment scale. Thus, we conclude that response observations (dynamics and patterns, i.e., indicators of function) were well suited to describing processes at the observational scale. Especially the use of 2-D time-lapse GPR measurements, providing detailed subsurface response patterns, as well as the combination of stream-centered and hillslope-centered approaches, allowed us to link processes and put them in a larger context. Transfer to other scales beyond observational scale and generalizations, however, rely on the knowledge of structures (form) and remain speculative. The complementary approach with a methodological focus on form (i.e., structure exploration) is presented and discussed in the companion paper by Jackisch et al. (2017). Y1 - 2017 U6 - https://doi.org/10.5194/hess-21-3727-2017 SN - 1027-5606 SN - 1607-7938 VL - 21 SP - 3727 EP - 3748 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Jackisch, Conrad A1 - Angermann, Lisa A1 - Allroggen, Niklas A1 - Sprenger, Matthias A1 - Blume, Theresa A1 - Tronicke, Jens A1 - Zehe, Erwin T1 - Form and function in hillslope hydrology: in situ imaging and characterization of flow-relevant structures JF - Hydrology and earth system sciences : HESS N2 - The study deals with the identification and characterization of rapid subsurface flow structures through pedo- and geo-physical measurements and irrigation experiments at the point, plot and hillslope scale. Our investigation of flow-relevant structures and hydrological responses refers to the general interplay of form and function, respectively. To obtain a holistic picture of the subsurface, a large set of different laboratory, exploratory and experimental methods was used at the different scales. For exploration these methods included drilled soil core profiles, in situ measurements of infiltration capacity and saturated hydraulic conductivity, and laboratory analyses of soil water retention and saturated hydraulic conductivity. The irrigation experiments at the plot scale were monitored through a combination of dye tracer, salt tracer, soil moisture dynamics, and 3-D time-lapse ground penetrating radar (GPR) methods. At the hillslope scale the subsurface was explored by a 3-D GPR survey. A natural storm event and an irrigation experiment were monitored by a dense network of soil moisture observations and a cascade of 2-D time-lapse GPR "trenches". We show that the shift between activated and non-activated state of the flow paths is needed to distinguish structures from overall heterogeneity. Pedo-physical analyses of point-scale samples are the basis for sub-scale structure inference. At the plot and hillslope scale 3-D and 2-D time-lapse GPR applications are successfully employed as non-invasive means to image subsurface response patterns and to identify flow-relevant paths. Tracer recovery and soil water responses from irrigation experiments deliver a consistent estimate of response velocities. The combined observation of form and function under active conditions provides the means to localize and characterize the structures (this study) and the hydrological processes (companion study Angermann et al., 2017, this issue). Y1 - 2017 U6 - https://doi.org/10.5194/hess-21-3749-2017 SN - 1027-5606 SN - 1607-7938 VL - 21 SP - 3749 EP - 3775 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Tronicke, Jens A1 - Paasche, Hendrik T1 - Integrated interpretation of 2D ground-penetrating radar, P-, and S-wave velocity models in terms of petrophysical properties BT - assessing uncertainties related to data inversion and petrophysical relations JF - Interpretation : a journal of subsurface characterization N2 - Near-surface geophysical techniques are extensively used in a variety of engineering, environmental, geologic, and hydrologic applications. While many of these applications ask for detailed, quantitative models of selected material properties, geophysical data are increasingly used to estimate such target properties. Typically, this estimation procedure relies on a two-step workflow including (1) the inversion of geophysical data and (2) the petrophysical translation of the inverted parameter models into the target properties. Standard deterministic implementations of such a quantitative interpretation result in a single best-estimate model, often without considering and propagating the uncertainties related to the two steps. We address this problem by using a rather novel, particle-swarm-based global joint strategy for data inversion and by implementing Monte Carlo procedures for petrophysical property estimation. We apply our proposed workflow to crosshole ground-penetrating radar, P-, and S-wave data sets collected at a well-constrained test site for a detailed geotechnical characterization of unconsolidated sands. For joint traveltime inversion, the chosen global approach results in ensembles of acceptable velocity models, which are analyzed to appraise inversion-related uncertainties. Subsequently, the entire ensembles of inverted velocity models are considered to estimate selected petrophysical properties including porosity, bulk density, and elastic moduli via well-established petrophysical relations implemented in a Monte Carlo framework. Our results illustrate the potential benefit of such an advanced interpretation strategy; i.e., the proposed workflow allows to study how uncertainties propagate into the finally estimated property models, while concurrently we are able to study the impact of uncertainties in the used petrophysical relations (e.g., the influence of uncertain, user-specified parameters). We conclude that such statistical approaches for the quantitative interpretation of geophysical data can be easily extended and adapted to other applications and geophysical methods and might be an important step toward increasing the popularity and acceptance of geophysical tools in engineering practice. Y1 - 2017 U6 - https://doi.org/10.1190/INT-2016-0081.1 SN - 2324-8858 SN - 2324-8866 VL - 5 IS - 1 SP - T121 EP - T130 PB - Society of Exploration Geophysicists CY - Tulsa ER - TY - JOUR A1 - Schennen, Stephan A1 - Tronicke, Jens A1 - Wetterich, Sebastian A1 - Allroggen, Niklas A1 - Schwamborn, Georg A1 - Schirrmeister, Lutz T1 - 3D ground-penetrating radar imaging of ice complex deposits in northern East Siberia JF - Geophysics N2 - Ice complex deposits are characteristic, ice-rich formations in northern East Siberia and represent an important part in the arctic carbon pool. Recently, these late Quaternary deposits are the objective of numerous investigations typically relying on outcrop and borehole data. Many of these studies can benefit from a 3D structural model of the subsurface for upscaling their observations or for constraining estimations of inventories, such as the local carbon stock. We have addressed this problem of structural imaging by 3D ground-penetrating radar (GPR), which, in permafrost studies, has been primarily used for 2D profiling. We have used a 3D kinematic GPR surveying strategy at a field site located in the New Siberian Archipelago on top of an ice complex. After applying a 3D GPR processing sequence, we were able to trace two horizons at depths below 20 m. Taking available borehole and outcrop data into account, we have interpreted these two features as interfaces of major lithologic units and derived a 3D cryostratigraphic model of the subsurface. Our data example demonstrated that a 3D surveying and processing strategy was crucial at our field site and showed the potential of 3D GPR to image geologic structures in complex ice-rich permafrost landscapes. Y1 - 2016 U6 - https://doi.org/10.1190/GEO2015-0129.1 SN - 0016-8033 SN - 1942-2156 VL - 81 SP - WA195 EP - WA202 PB - Society of Exploration Geophysicists CY - Tulsa ER - TY - JOUR A1 - Allroggen, Niklas A1 - Tronicke, Jens T1 - Attribute-based analysis of time-lapse ground-penetrating radar data JF - Geophysics N2 - Analysis of time-lapse ground-penetrating radar (GPR) data can provide information regarding subsurface hydrological processes, such as preferential flow. However, the analysis of time-lapse data is often limited by data quality; for example, for noisy input data, the interpretation of difference images is often difficult. Motivated by modern image-processing tools, we have developed two robust GPR attributes, which allow us to distinguish amplitude (contrast similarity) and time-shift (structural similarity) variations related to differences between individual time-lapse GPR data sets. We tested and evaluated our attributes using synthetic data of different complexity. Afterward, we applied them to a field data example, in which subsurface flow was induced by an artificial rainfall event. For all examples, we identified our structural similarity attribute to be a robust measure for highlighting time-lapse changes also in data with low signal-to-noise ratios. We determined that our new attribute-based workflow is a promising tool to analyze time-lapse GPR data, especially for imaging subsurface hydrological processes. Y1 - 2016 U6 - https://doi.org/10.1190/GEO2015-0171.1 SN - 0016-8033 SN - 1942-2156 VL - 81 SP - H1 EP - H8 PB - Society of Exploration Geophysicists CY - Tulsa ER - TY - JOUR A1 - Guillemoteau, Julien A1 - Simon, Francois-Xavier A1 - Lück, Erika A1 - Tronicke, Jens T1 - 1D sequential inversion of portable multi-configuration electromagnetic induction data JF - Near surface geophysics N2 - We present an algorithm that performs sequentially one-dimensional inversion of subsurface magnetic permeability and electrical conductivity by using multi-configuration electromagnetic induction sensor data. The presented method is based on the conversion of the in-phase and out-of-phase data into effective magnetic permeability and electrical conductivity of the equivalent homogeneous half-space. In the case of small-offset systems, such as portable electromagnetic induction sensors, for which in-phase and out-of-phase data are moderately coupled, the effective half-space magnetic permeability and electrical conductivity can be inverted sequentially within an iterative scheme. We test and evaluate the proposed inversion strategy using synthetic and field examples. First, we apply it to synthetic data for some highly magnetic environments. Then, the method is tested on real field data acquired in a basaltic environment to image a formation of archaeological interest. These examples demonstrate that a joint interpretation of in-phase and out-of-phase data leads to a better characterisation of the subsurface in magnetic environments such as volcanic areas. Y1 - 2016 U6 - https://doi.org/10.3997/1873-0604.2016029 SN - 1569-4445 SN - 1873-0604 VL - 14 SP - 423 EP - 432 PB - Wiley-VCH CY - Houten ER - TY - JOUR A1 - Rumpf, Michael A1 - Tronicke, Jens T1 - Assessing uncertainty in refraction seismic traveltime inversion using a global inversion strategy JF - Geophysical prospecting N2 - To analyse and invert refraction seismic travel time data, different approaches and techniques have been proposed. One common approach is to invert first-break travel times employing local optimization approaches. However, these approaches result in a single velocity model, and it is difficult to assess the quality and to quantify uncertainties and non-uniqueness of the found solution. To address these problems, we propose an inversion strategy relying on a global optimization approach known as particle swarm optimization. With this approach we generate an ensemble of acceptable velocity models, i.e., models explaining our data equally well. We test and evaluate our approach using synthetic seismic travel times and field data collected across a creeping hillslope in the Austrian Alps. Our synthetic study mimics a layered near-surface environment, including a sharp velocity increase with depth and complex refractor topography. Analysing the generated ensemble of acceptable solutions using different statistical measures demonstrates that our inversion strategy is able to reconstruct the input velocity model, including reasonable, quantitative estimates of uncertainty. Our field data set is inverted, employing the same strategy, and we further compare our results with the velocity model obtained by a standard local optimization approach and the information from a nearby borehole. This comparison shows that both inversion strategies result in geologically reasonable models (in agreement with the borehole information). However, analysing the model variability of the ensemble generated using our global approach indicates that the result of the local optimization approach is part of this model ensemble. Our results show the benefit of employing a global inversion strategy to generate near-surface velocity models from refraction seismic data sets, especially in cases where no detailed a priori information regarding subsurface structures and velocity variations is available. KW - Inversion KW - Seismic refraction KW - Uncertainty Y1 - 2015 U6 - https://doi.org/10.1111/1365-2478.12240 SN - 0016-8025 SN - 1365-2478 VL - 63 IS - 5 SP - 1188 EP - 1197 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Guillemoteau, Julien A1 - Tronicke, Jens T1 - Non-standard electromagnetic induction sensor configurations: Evaluating sensitivities and applicability JF - Journal of applied geophysics N2 - For near surface geophysical surveys, small-fixed offset loop-loop electromagnetic induction (EMI) sensors are usually placed parallel to the ground surface (i.e., both loops are at the same height above ground). In this study, we evaluate the potential of making measurements with a system that is not parallel to the ground; i.e., by positioning the system at different inclinations with respect to ground surface. First, we present the Maxwell theory for inclined magnetic dipoles over a homogeneous half space. By analyzing the sensitivities of such configurations, we,show that varying the angle of the system would result in improved imaging capabilities. For example, we show that acquiring data with a vertical system allows detection of a conductive body with a better lateral resolution compared to data acquired using standard horizontal configurations. The synthetic responses are presented for a heterogeneous medium and compared to field data acquired in the historical Park Sanssouci in Potsdam, Germany. After presenting a detailed sensitivity analysis and synthetic examples of such ground conductivity measurements, we suggest a new strategy of acquisition that allows to better estimate the true distribution of electrical conductivity using instruments with a fixed, small offset between the loops. This strategy is evaluated using field data collected at a well-constrained test-site in Horstwalde (Germany). Here, the target buried utility pipes are best imaged using vertical system configurations demonstrating the potential of our approach for typical applications. (C) 2015 Elsevier B.V. Pill rights reserved. KW - Electromagnetics KW - EMI sensors KW - Loop-loop systems KW - Near surface geophysics KW - Civil engineering KW - Sensitivity analysis Y1 - 2015 U6 - https://doi.org/10.1016/j.jappgeo.2015.04.008 SN - 0926-9851 SN - 1879-1859 VL - 118 SP - 15 EP - 23 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Allroggen, Niklas A1 - van Schaik, N. Loes M. B. A1 - Tronicke, Jens T1 - 4D ground-penetrating radar during a plot scale dye tracer experiment JF - Journal of applied geophysics N2 - Flow phenomena in the unsaturated zone are highly variable in time and space. Thus, it is challenging to measure and monitor such processes under field conditions. Here, we present a new setup and interpretation approach for combining a dye tracer experiment with a 4D ground-penetrating radar (GPR) survey. Therefore, we designed a rainfall experiment during which we measured three surface-based 3D GPR surveys using a pair of 500 MHz antennas. Such a survey setup requires accurate acquisition and processing techniquesto extract time-lapse information supporting the interpretation of selected cross-sections photographed after excavating the site. Our results reveal patterns of traveltime changes in the measured GPR data, which are associated with soil moisture changes. As distinct horizons are present at our site, such changes can be quantified and transferred into changes in total soil moisture content. Our soil moisture estimates are similar to the amount of infiltrated water, which confirms our experimental approach and makes us confident for further developing this strategy, especially, with respect to improving the temporal and spatial resolution. (C) 2015 Elsevier B.V. All rights reserved. KW - Ground penetrating radar KW - Time-lapse imaging KW - Brilliant blue Y1 - 2015 U6 - https://doi.org/10.1016/j.jappgeo.2015.04.016 SN - 0926-9851 SN - 1879-1859 VL - 118 SP - 139 EP - 144 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Tronicke, Jens A1 - Allroggen, Niklas T1 - Toward automated delineation of ground-penetrating radar facies in clastic sediments: An example from stratified glaciofluvial deposits JF - Geophysics N2 - Ground-penetrating radar (GPR) is an established geophysical method to explore near-surface sedimentary environments. Interpreting GPR images is largely based on manual procedures following concepts known as GPR facies analysis. We have developed a novel strategy to distinguish GPR facies in a largely automated and more objective manner. First, we calculate 13 textural attributes to quantify GPR reflection characteristics. Then, this database is reduced using principal component analysis. Finally, we image the dominating principal components using composite imaging and classify them using standard clustering methods. The potential of this work-flow is evaluated using a 2D GPR field example collected across stratified glaciofluvial deposits. Our results demonstrate that the derived facies images are well correlated with the composition and the porosity of the sediments as known from independent borehole logs. Our analysis strategy eases and improves the interpretability of GPR data and will help in a variety of geologic and hydrological problems. Y1 - 2015 U6 - https://doi.org/10.1190/GEO2015-0188.1 SN - 0016-8033 SN - 1942-2156 VL - 80 IS - 4 SP - A89 EP - A94 PB - Society of Exploration Geophysicists CY - Tulsa ER - TY - JOUR A1 - Allroggen, Niklas A1 - Tronicke, Jens A1 - Delock, Marcel A1 - Böniger, Urs T1 - Topographic migration of 2D and 3D ground-penetrating radar data considering variable velocities JF - Near surface geophysics N2 - We present a 2D/3D topographic migration scheme for ground-penetrating radar (GPR) data which is able to account for variable velocities by using the root mean square (rms) velocity approximation. We test our migration scheme using a synthetic 2D example and compare our migrated image to the results obtained using common GPR migration approaches. Furthermore, we apply it to 2D and 3D field data. These examples are recorded across common subsurface settings including surface topography and variations in the GPR subsurface velocity field caused by a shallow ground water table. In such field settings, our migration strategy provides well focused images of commonoffset GPR data without the need for a detailed interval velocity model. The synthetic and field examples demonstrate that our topographic migration scheme allows for accurate GPR imaging in the presence of variations in surface topography and subsurface velocity. Y1 - 2015 U6 - https://doi.org/10.3997/1873-0604.2014037 SN - 1569-4445 SN - 1873-0604 VL - 13 IS - 3 PB - European Association of Geoscientists & Engineers CY - Houten ER -