Andreas Kemna | Bonn Universität (original) (raw)

Papers by Andreas Kemna

Eos, Transactions American Geophysical Union, 2009

Hydrology and Earth System Sciences, 2011

Journal of Hydrology, 2012

AGU Fall Meeting Abstracts, Dec 1, 2010

Developing predictive models of reservoirs is often complicated by the spatial heterogeneities an... more Developing predictive models of reservoirs is often complicated by the spatial heterogeneities and the different scales which control flow and transport processes. In numerous studies over the past two decades, geophysical imaging techniques have proved very useful for reservoir characterization. However, the loss of resolution and the non-uniqueness of standard solutions to inverse problems strongly limit the use of such deterministic imaging approaches. On the other hand, the use of common geostatistical ...

Environmental Science & Technology, 2009

Journal of Colloid and Interface Science, 2008

The low-frequency conductivity response of water-saturated packs of glass beads reflects a combin... more The low-frequency conductivity response of water-saturated packs of glass beads reflects a combination of two processes. One process corresponds to the polarization of the mineral/water interface coating the surface of the grains. The other process corresponds to the Maxwell-Wagner polarization associated with accumulation of the electrical charges in the pore space of the composite medium. A model of low-frequency conductivity dispersion is proposed. This model is connected to a triple-layer model of electrochemical processes occurring at the surface of silica. This model accounts for the partition of the counterions between the Stern and the diffuse layers. The polarization of the mineral/water interface is modeled by the electrochemical polarization model of Schurr for a spherical grain. We take into account also the DC surface conductivity contribution of protons of the sorbed water and the contribution of the diffuse layer. At the scale of a macroscopic representative elementary volume of the porous material, the electrochemical polarization of a single grain is convoluted with the grain size distribution of the porous material. Finally, the Maxwell-Wagner polarization is modeled using the complex conductivity of a granular porous medium obtained from the differential effective medium theory. The predictions of this model agree well with experimental data of spectral induced polarization. Two peaks are observed at low frequencies in the spectrum of the phase. The first peak corresponds to the distribution of the size of the beads and the second peak is due to the roughness of the grains.

Vadose Zone Journal, 2009

ABSTRACT Temporal mapping of the three-dimensional spatial distribution of solute transport in so... more ABSTRACT Temporal mapping of the three-dimensional spatial distribution of solute transport in soils is needed for an improved understanding of the underlying processes. Numerous studies have confirmed that Brilliant Blue imaging provides spatially highly resolved information on solute transport In soils. A drawback of the method, however, is its destructive character, which prevents three-dimensional mapping of the temporal evolution of Brilliant Blue plumes or fronts. In this study, we determined that the negative ionic charge of the Brilliant Blue molecule for moderately acid and basic environments provides an electrical conductivity contrast that can be detected by means of time domain reflectometry (TDR) and electrical resistivity tomography (ERT). Time-lapse ERT supplies three-dimensional spatiotemporally resolved image data through minimally invasive measurements but with limited spatial resolution. A joint application of Brilliant Blue imaging and (time-lapse) ERT offers pote

Given the importance of soil and aquifer structures on flow and transport processes, tomographic ... more Given the importance of soil and aquifer structures on flow and transport processes, tomographic methods enabling a non-invasive monitoring of these processes are of special interest. In this contribution, we demonstrate some applications of electrical resistivity tomography (ERT) for monitoring flow and transport processes. A first application deals with monitoring of salt tracer transport in the soil or groundwater. During groundwater tracer studies the tracer breakthrough was monitored using local groundwater samplers and ERT in two reference planes perpendicular to the mean flow direction. A numerical study illustrated that conditioning the ERT inversion on local salinity measurements may improve the quality of the ERT images considerably. Because of the small spatio-temporal consistency of groundwater sampler measurements, i.e. groundwater concentration measurements varied over small distances and were not consistent in two consecutive tracer experiments, the use of these measu...

Funders: Fonds pour la formation à la Recherche dans l'Industrie et dans l'Agriculture ... more Funders: Fonds pour la formation à la Recherche dans l'Industrie et dans l'Agriculture (Communauté française de Belgique)-FRIA; Fonds de la Recherche Scientifique (Communauté française de Belgique)-FRS-FNRS

Proceedings SWIM21, 21st Salt …, 2010

[en] The integrated water resource management problems require studying efficiently seawater intr... more [en] The integrated water resource management problems require studying efficiently seawater intrusion at local and regional scale and identifying in real time the seawater/freshwater interface dynamic. Hydrogeological modeling is widely used to predict seawater intrusion if ...

Near Surface Geophysics, 2009

IEEE Sensors Journal, 2005

A magnetoelectrical resistivity measurement system is proposed, which combines measurement of the... more A magnetoelectrical resistivity measurement system is proposed, which combines measurement of the electric potential and the magnetic field due to a current injection into a sample. Measurement of the electric potential, as well as the injected current, is similar to traditional electrical resistivity tomography (ERT) data acquisition. For the magnetic field measurements, 24 sensor modules have been developed using three

Measurement Science and Technology, 2008

Spectral impedance measurements are receiving increased attention with regard to the characteriza... more Spectral impedance measurements are receiving increased attention with regard to the characterization of soils, sediments and rocks, particularly in terms of the internal rock structure, the mineralogical composition and the chemistry of fluids contained in porous rocks. In fluid-saturated, porous sedimentary rocks, which are of particular relevance for many hydrological and environmental problems, the polarization processes that give rise to