Quantitative exploration of aquifer systems – Improvements of the surface nuclear magnetic resonance application
Begin of project: January 1, 2009
End of project: December 31, 2013
Status of project: December 31, 2013
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The geophysical application of surface nuclear magnetic resonance (surface NMR) measures the distribution of volumetric water content in the subsurface non-invasively. Moreover, using the NMR relaxation times a proxy for the mean pore size is provided that allows the lithological characterization of the subsurface and, if sufficient calibration data is available, the estimation of hydraulic conductivity. However, the application of the surface NMR method suffers in practice from very low signal voltages (10 to 1000 nV) and thus from high sensitivity to the surrounding electromagnetic (EM) noise conditions. The development of multi-channel measurement equipment (Walsh, 2008; Dlugosch et al., 2011) was a breakthrough in the research field of surface NMR, because this technology allows remote references for online detection of surrounding noise. This additional data can be used for predicting the noise signal in the NMR channel and thus for cancelling noise much more effectively than common bandpass or notch filters. The objective of this research project was to test and assess the new technical improvements and to generate further development for optimized usage of the multi-channel technology.
Abb.1: Processing-Schritte vom gemessenen Signal bis hin zum exponentiell gefitteten Ergebnis im Zeitbereich (linke Spalte) und Frequenzbereich (rechte Spalte): (a) Rohdaten mit harmonischen Störanteilen und Spikes, (b) Eliminierung der Spikes mittels Wavelet-Filterung, (c) Unterdrückung der harmonischen Störanteile und (d) Stapelung und exponentielle Anpassung des resultierenden Signals. Amplitude und Abklingzeit stehen nun zur weiteren Verarbeitung/Inversion zur Verfügung
Source: BGR
Within the scope of this project different EM noise features were investigated and strategies to remove them from surface NMR signals were developed and tested. Harmonic disturbances from power lines or railways could be cancelled out very successively. Depending on the specific measurement location, a decrease of noise level by a factor of up to 20 could be observed. However, our findings also showed that the individual noise characteristics at the site of investigation require an individual post-processing strategy for realizing the most effective noise minimization. At many places we observed strong variations in frequency or amplitude of the harmonic noise within short periods of time (less than 100 ms) or very short noise signals with enormous amplitudes (spikes). Both features can limit the application of the remote reference technique and must be considered if present. In cooperation with our colleagues at the Leibniz-Institute for Applied Geophysics, we developed optimized noise cancellation strategies for both spiky noise and harmonics with strong temporal variations (Fig. 1, Costabel and Müller-Petke, 2014; Müller-Petke and Costabel, 2014). The developed processing software has been made available to the scientific community by including it into the software package MRSmatlab (Müller-Petke et al., 2012, 2016).
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In addition to the common application of surface NMR for aquifer characterization, we tested the method and the novel data processing strategies for moisture investigations in the vadose zone. Surface NMR signals from unsaturated materials are even weaker than usual with less than 10 ms and thus, the use of surface NMR measurement for characterizing the vadose zone was limited so far. Within this project, we successfully measured partially saturated regions in the vadose zone (Fig. 2, Costabel and Günther, 2014). Future research is planned to establish the surface NMR method for characterizing the vadose zone and to develop the corresponding interpretation of surface NMR data.
References:
- Costabel S. und Müller-Petke M. (2014). Despiking of magnetic resonance signals in time and wavelet domain. Near Surface Geophysics 12(2), 185 – 197.
- Costabel, S., und Günther, T. (2014). Noninvasive Estimation of Water Retention Parameters by Observing the Capillary Fringe with Magnetic Resonance Sounding. Vadose Zone Journal 13 (6).
- Dlugosch, R., M. Müller-Petke, T. Günther, S. Costabel, and U. Yaramanci (2011). Assessment of the potential of a new generation of surface nuclear magnetic resonance instruments. Near Surf. Geophys. 9, 89 – 102.
- Müller-Petke M. and Costabel S. (2014). Comparison and optimal parameter setting of reference-based harmonic noise cancellation in time and frequency domain for surface-NMR. Near Surface Geophysics 12(2), 199 – 210.
- Müller-Petke, M., Walbrecker, J., Hertrich, M. (2012). MRSMATLAB2.0 – Modules for MRS modeling inversion and data processing. MRSMATLAB2.0 – Modules for MRS modeling inversion and data processing. 25th Symposium on the Application of Geophpysics to Engineering & Environmental Problems, Tucson, Arizona.
- Müller-Petke, M., Braun, M., Hertrich, M., Costabel, S., and Walbrecker, J. (2016). MRSmatlab – A software tool for processing, modeling, and inversion of magnetic resonance sounding data. Geophysics 81 (4), WB9 – WB21. Doi: 10.1190/GEO2015-0461.1.
- Walsh, D. (2008). Multi-channel surface NMR instrumentation and software for 1D/2D groundwater investigations. Journal of Applied Geophysics, 66(3-4), 140–150.
Posters and Presentations:
Costabel, S. and Müller-Petke, M. (2011). Remote-Reference-Strategien zur Rauschunterdrückung bei Messungen de Oberflächen-Nuklearmagnetischen Resonanz (SNMR). Tagungsband der 71. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, 21. – 24. Februar, Köln, Deutschland.
- Müller-Petke, M., Costabel, S., and Yaramanci, U. (2011). Abstrakt, Tagungsband DGG 2011 Tagungsband der 71. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, 21. – 24. Februar, Köln, Deutschland.
Costabel, S. and Günther, T. (2012). Magnetische Resonanz Sondierung zur Parametrisierung der kapillaren Aufstiegszone. 72. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, 5. – 8. März, Hamburg, Deutschland.
Seibertz, K., Günther, T., and Costabel, S. (2012). Magnet-Resonanz-Sondierungen (MRS) für die Erstellung von hydrogeologischen Schnitten am Beispiel Brandenburgisches Havelland. 72. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, 5. – 8. März, Hamburg, Deutschland.
Costabel, S., Noell, U. and Ganz, C. (2012). Non-invasive investigation of the saturated/unsaturated zone with magnetic resonance sounding – a field example at the testsite Fuhrberger Feld near Hannover, Germany. Geophysical Research Abstracts (14), Proceedings of EGU General Assembly 2012, Vienna, Austria.
Costabel, S. and Günther, T. (2012). Direct inversion for water retention parameters from MRS measurements in the saturated/unsaturated zone – a sensitivity study. Presentation at 5th International Meeting on Magnetic Resonance, 25. – 27. September, Hannover, Germany.
Müller-Petke, M. and Costabel, S. (2012). A comparison of harmonic noise cancellation concepts. Poster at 5th International Meeting on Magnetic Resonance - Abstract, 25. – 27. September, Hannover, Germany.
Costabel, S. and Müller-Petke, M. (2012). MRS noise investigations with focus on optimizing the measurement setup in the field. Poster at 5th International Meeting on Magnetic Resonance, 25. – 27. September, Hannover, Germany.
Costabel, S. and Müller-Petke, M. (2012). Identification and elimination of spiky noise features in MRS data. Poster at 5th International Meeting on Magnetic Resonance, 25. – 27. September, Hannover, Germany.
Costabel, S. and Noell, U. (2012). Surface Nuclear Magnetic Resonance for non-invasive observation of the vadose zone. Presentation at 2nd International Conference on Hydropedology (PDF, 1 MB) Presentation at 2nd International Conference on Hydropedology, 22 – 27 July, Leibzig, Germany.
Costabel, S., Günther, T., and Meyer, U. (2012). A feasibility study on the estimation of water retention parameters from surface nuclear magnetic resonance measurements in the vadose zone.
Müller-Petke, M. and Costabel, S. (2013) Müller-Petke, M. and Costabel, S. (2013) Surface-NMR in Urban Area . A No Go? Proceedings of Near Surface Geoscience, 19th European Meeting of Environmental and Engineering Geophysics, 9 – 11 September, Bochum, Germany, 9 – 11 September, Bochum, Germany.