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TU Berlin

Inhalt des Dokuments

Monitoring of Water Content Distributions inside a Lysimeter with GPR-Tomography

Principal investigator: Prof. Dr. U. Yaramanci
Investigators: Dr. H. Stoffregen, J. Schmalholz, S. Strehl
Funding: Forschungszentrum Jülich GmbH
Duration: 1.1.2002 bis 31.12.2005
Cooperation: Forschungszentrum Jülich GmbH

Description of the Project:
A lysimeter is a vessel containing soil placed with its top edge to the ground surface. Lysimeter are used to study phases of the hydrological cycle in terms of water content and dynamics, e.g. infiltration, evapotranspiration or runoff. Lysimeter provide a good alternative to carry out and test various methods or theoretical theories under relative undisturbed circumstances. In cooperation with the Institute of Chemistry and Dynamics of the Geosphere, IV Agrosphere (ICG-IV) of the Forschungszentrum Jülich GmbH, the solute transport inside a lysimeter ought to be investigated.
To avoid the inevitable problem of the boundary conditions for electromagnetic geophysical methods of a normal lysimeter with its metal wall, an alternative had to be found. Therefore PVC-cylinders were chosen with 1.5 m height and 1.2 m diameter. The dielectric permittivity of soils depends strongly on the water content. Therefore, GPR was used as it can provide non-invasive high-resolution information regarding the distribution of the dielectric permittivity of a heterogeneous medium. Because the used lysimeter has PVC walls tomographic measurements can be performed.
Considering the relatively small dimensions of the lysimeter (1.2m diameter, 1.5m height) and the armament with sensors for other methods, a pair of shielded antennas was chosen with centre frequencies of approx. 750 MHz. In April and September 2002 first measurements were carried out on a filled but unequipped lysimeter to check signal quality, feasibility as well as the needed time to gather a dataset under ideal conditions. Furthermore pot irrigation tests were made in 2002 and 2004 to estimate the actual resolution with the available equipment.
To derive the volumetric water content, the calculated dielectric permittivity values have to be transformed. Based on the soil inside the lysimeter (approx. 80% sand, 15% silt and 5% clay with approx. 40% porosity) appropriate mixing formulas for bulk dielectric permittivity have to be chosen and compared to the results gathered from alternative methods.

Partially flodded lysimeter with receiver antenna (GPR-System RAMAC, Mala GeoScience) held to the lysimeter wall.
View of the equipped lysimeter from inside the lysimeter hall.
Results of the irrigation experiment. Here the change of the volumetric water content (VWC) at a lysimeter height of 80 cm (approx. 40 cm below ground level) is shown over a time of almost 600 min after the initial irrigation

Click file to see an animated version.

Recent Publications:
Schmalholz, J., Stoffregen, H., Kemna, A., and Yaramanci, U., 2004. Imaging of water content distributions inside a lysimeter using GPR tomography: Vadose Zone Journal, 3:1106-1115 (2004).
Schmalholz, J., Müller, M., Yaramanci, U., Kemna, A., and Stoffregen, H., 2004. Small scale determination of volumetric water content distribution in the uppermost soil: Proc. 10th Int. Conf. Ground Penetrating Radar, Delft, June 21-24, HYD.1, 4 p.
Schmalholz, J., Kemna, A., Müller, M., Stoffregen, H., and Yaramanci, U., 2004. Soil moisture dynamics with time lapse GPR: Extended Abstract Book "Near Surface 2004" ° 10th European Mtg. of Environmental and Engineering Geophysics, Eur. Assn. Geosci. Eng., A026, 4 p.

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