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End date: 2024 × Start date: 2020 × DDC: 550 × DDC: 620 × WGL Institute: LIAG ×

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Now showing 1 - 6 of 6
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    Evaluation of spectral induced polarization field measurements in time and frequency domain
    (Amsterdam [u.a.] : Elsevier Science, 2020) Martin, Tina; Günther, Thomas; Orozco, Adrian Flores; Dahlin, Torleif
    Spectral induced polarization (SIP) measurements have been demonstrated to correlate with important parameters in hydrogeological and environmental investigations. Although SIP measurements were often collected in the frequency domain (FDIP), recent developments have demonstrated the capabilities to solve for the frequency-dependence of the complex conductivity through measurements collected in the time domain (TDIP). Therefore, the aim of our field investigations is a comparison of the measured frequency-dependence at a broad frequency range resolved through FDIP and TDIP. In contrast to previous studies, we conducted measurements with different instruments and measuring technologies for both FDIP and TDIP. This allows for investigating the robustness of different measurements and assessing various sources of errors, for the assessment of the advantages and drawbacks from different measuring techniques. Our results demonstrate that data collected through different instruments are consistent. Apparent resistivity measurements as well as the inversion results revealed quantitatively the same values for all instruments. The measurements of the IP effect are also comparable, particularly FDIP readings in the low frequencies (< 10 Hz) revealed to be quantitatively the same for different instruments. TDIP measurements are consistent for data collected with both devices. As expected, the spatial distribution of the values is also consistent for low frequency data (in FDIP) and late times measurements in TDIP (> 0.1 s). However, data quality for higher frequencies in FDIP (i.e., early times in TDIP) show larger variations, which reflects the differences between the instruments to deal with the electromagnetic contamination of the IP data. Concluded in general, the different instruments and measuring techniques can provide consistent responses for varying signal-to-noise ratio and measuring configurations. © 2020 The Authors
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    Comparison of novel semi-airborne electromagnetic data with multi-scale geophysical, petrophysical and geological data from Schleiz, Germany
    (Amsterdam [u.a.] : Elsevier Science, 2020) Steuer, Annika; Smirnova, Maria; Becken, Michael; Schiffler, Markus; Günther, Thomas; Rochlitz, Raphael; Yogeshwar, Pritam; Mörbe, Wiebke; Siemon, Bernhard; Costabel, Stephan; Preugschat, Benedikt; Ibs-von Seht, Malte; Zampa, Luigi Sante; Müller, Franz
    In the framework of the Deep Electromagnetic Sounding for Mineral EXploration (DESMEX) project, we carried out multiple geophysical surveys from regional to local scales in a former mining area in the state of Thuringia, Germany. We prove the applicability of newly developed semi-airborne electromagnetic (EM) systems for mineral exploration by cross-validating inversion results with those of established airborne and ground-based investigation techniques. In addition, supporting petrophysical and geological information to our geophysical measurements allowed the synthesis of all datasets over multiple scales. An initial regional-scale reconnaissance survey was performed with BGR's standard helicopter-borne geophysical system deployed with frequency-domain electromagnetic (HEM), magnetic and radiometric sensors. In addition to geological considerations, the HEM results served as base-line information for the selection of an optimal location for the intermediate-scale semi-airborne EM experiments. The semi-airborne surveys utilized long grounded transmitters and two independent airborne receiver instruments: induction coil magnetometers and SQUID sensors. Due to the limited investigation depth of the HEM method, local-scale electrical resistivity tomography (ERT) and long-offset transient electromagnetic (LOTEM) measurements were carried out on a reference profile, enabling the validation of inversion results at greater depths. The comparison of all inversion results provided a consistent overall resistivity distribution. It further confirmed that both semi-airborne receiver instruments achieve the bandwidth and sensitivity required for the investigation of the resistivity structure down to 1 km depth and therewith the detection of deeply seated earth resources. A 3D geological model, lithological and geophysical borehole logs as well as petrophysical investigations were integrated to interpret of the geophysical results. Distinct highly-conductive anomalies with resistivities of less than 10 Om were identified as alum shales over all scales. Apart from that, the petrophysical investigations exhibited that correlating geophysical and geological information using only one single parameter, such as the electrical resistivity, is hardly possible. Therefore, we developed a first approach based on clustering methods and self-organizing maps (SOMs) that allowed us to assign geological units at the surface to a given combination of geophysical and petrophysical parameters, obtained on different scales. © 2020 The Authors
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    Application of adiabatic pulses for magnetic Resonance Sounding – Pulse shapes and resolution
    (Amsterdam [u.a.] : Elsevier Science, 2020) Dlugosch, Raphael; Müller-Petke, Mike
    Magnetic Resonance Sounding (MRS) can image the spatial distribution of hydrologically relevant parameters in in the subsurface. However, the application of MRS is often limited by its low signal-to-noise ratio. The use of adiabatic excitation pulses show promising features to overcome this limitation. In this work, we study practical considerations when applying adiabatic pulses for MRS, i.e. calculation of the sensitivity kernel for varying pulse shapes and vertical resolution. The pulse shape is crucial for the performance of adiabatic pulses. We investigate the shapes of adiabatic pulses recorded during a MRS and observe small systematic deviations from the theoretical predicted pulse shape and variations between different pulse strengths. We show that the overall impact on the obtained sounding curve and inversion result was small. This enables to limit the time consuming modelling of the spin dynamic to one representative pulse shape, which significantly speeds up the calculation of the sensitivity kernel, necessary for the interpretation of MRS. Additionally, we show that on-resonance excitation generally outperforms adiabatic excitation concerning vertical resolution and depth of investigation (both up to a factor of two). This is true for a wide range of noise conditions. For a very shallow depth interval compared to the loop size, however, adiabatic excitation features improved imaging capabilities. © 2020 The Authors
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    Classification of slag material by spectral induced polarization laboratory and field measurements
    (Amsterdam [u.a.] : Elsevier Science, 2021) Martin, Tina; Günther, Thomas; Weller, Andreas; Kuhn, Kerstin
    Historical slag dumps are of increasing interest due to economic, environmental or archaeological reasons. Geophysical investigations can help accessing the potential reuse of slag material to recover metallic raw material or for the estimation of the hazard potential of the buried slag material due to dissolution occurrence. In our study, we have investigated various slag material in the laboratory with the spectral induced polarization (SIP) method, obtained from different historical slag dumps, located in the Harz Mountains, Germany. We also present SIP results from field measurements at a historical slag dump where most of the slag samples reveal high amounts of iron, zinc, silica, and barium. Our results reveal a discrimination between three different slag grades (low, medium, high) by using the imaginary conductivity σ″ at a medium frequency (1–10 Hz) in both laboratory and field. Furthermore, additional information is obtained by a classification based on the spectral polarization behaviour and considering the field frequency range (0.1 Hz – 100 Hz). Five different types of spectra (ascending, descending, constant, maximum and minimum type) can be discriminated and recognized in the laboratory and in distinct areas of the slag dump. Even though a direct comparison between the laboratory and field results still needs to be proven, the buried slag material can be differentiated from the surrounding material by the polarization magnitude.
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    Non-remote reference noise cancellation - using reference data in the presence of surface-NMR signals
    (Amsterdam [u.a.] : Elsevier Science, 2020) Müller-Petke, Mike
    Surface-NMR measurements commonly suffer from low signal-to-noise ratios. In recent years, with the introduction of multi-channel surface-NMR instruments, the technique of remote-reference noise cancellation (RNC) was developed and significantly improved the applicability of surface-NMR. The current formulation of RNC requires a reference loop to be placed a remote distance from the transmitter loop such that no NMR signal is recorded. Reference loops placed at non-remote distances have been envisaged to provide both improved noise cancellation performance and field efficiency; however, the concept has not been previously applied because the theoretical framework was missing. In this paper, the theoretical framework is presented. It is demonstrated that reference loops placed at non-remote distances provide superior noise cancellation performance. Considerations for placing the reference loop relative to the transmitter loop are provided, and the theoretical framework is evaluated based on a semi-synthetic example using real field noise and synthetic surface-NMR data. © 2020
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    S-wave seismic imaging of near-surface sediments using tailored processing strategies
    (Amsterdam [u.a.] : Elsevier Science, 2020) Burschil, Thomas; Buness, Hermann
    Reflection seismic imaging using horizontally-polarized S-waves (SH) can increase resolution and it could be cost-efficient compared to the common use of P-waves. However, since S-wave application often delivers varying data quality, appropriate processing schemes are required for particular imaging and interpretation purposes. In this paper, we present four tailored processing strategies that are applied to SH-wave data acquired in an overdeepened Quaternary basin in the Alpine foreland, the Tannwald Basin. The applied processing schemes consist of (1) processing using a short automatic gain control window that enhances structural details and highlights small-scale structures, (2) offset restriction indicating that relative small offsets are sufficient for adequate imaging, which offers reduced field operation costs, (3) coherency-enhancement that reveals large-scale structures for interpretation, and (4) adapted amplitude scaling that enables structural comparison of P-wave and S-wave seismic sections. With respect to P-wave data measured on the same profile, we demonstrate the benefits of the S-wave seismic reflection method. P-waves offer robust imaging results, but S-waves double the resolution, better depict shallow reflections, and may image reflectors in areas where the P-wave struggles. At least for the Tannwald Basin, S-wave imaging is also more cost-efficient than P-wave imaging. © 2020 The Authors