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| Titel |
Low Field NMR of Water in Soils. A Case of Study. |
| VerfasserIn |
O. Sucre, A. Pohlmeier, F. Casanova, B. Blümich |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030273
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| Zusammenfassung |
| The evolution of water in soils is a physical phenomenon of importance in soil
science and climatology. While most investigations of soil moisture are performed
inside large superconducting magnets in the laboratory, it is advantageous to do such
investigations with mobile NMR equipment in the field. As a part of a DFG-funded
interdisciplinary project (TR32), this work establishes preliminary results from
the use of mobile NMR to measure moisture in soil columns. To demonstrate the
ability of the NMR technique to follow the drying process of water in soils, daily
moisture measurements were performed with a mobile NMR endoscope on three
different types of soil (silt, sand, and a natural soil) during an one-step outflow
experiment. The soils were packed in columns approximately one meter high. The NMR
measurements were cross-validated by repetitive measurements of the mass drift
due to the drying process. The NMR-endoscope exhibits a cylindrical geometry
incorporating the principle of the u-shaped NMR-MOUSE. It could be raised and lowered
inside a plastic tube (1 mm thick) in the soil column similar to a wire-line logging
tool. Working with a frequency of 8.73 MHz, the sensitive volume has a depth of 2
mm, avoiding any boundary effects that might arise due to the tube wall. For the
purpose of quantitative analysis, the water evolution (described by the Richards
Equation) was modelled with the Hydrus1D Program, taking into account the boundary
conditions under which the experiments were carried out. Out of these simulations,
an assessment of the hydraulic parameters (Ks, α, n and l of the Van Genuchten
model) of the soil is achieved. Experimental aspects such as the optimization of the
endoscope, the statistical uncertainty, and the noise shielding are discussed as well. |
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