Near Surface Geophysics

Geoelectrical and electromagnetic measurements are well suited to investigate the first centimeters to 100 m of the subsurface. Therefore they are used for various applications in hydrogeology, engineering and environmental geopyhsics, archaeology, agriculture and soil sciences.

Continuous DC resistivity measurements

Capacitively coupled geoelectrics using the Ohmmapper

Unlike usual geoelectrical instruments, the OhmMapper device allows for a continuous resistivity measurements by using capacitive coupling. The preliminary results show that it is well suited for investigation of the first 15-20 m depth. It is thus a good complement, particularly to Georadar/GPR measurements.

Underwater measurements using a geoelectrical streamer

The investigation of the subbottom sediments if of utmost importance for the coastal research, but also for industrial processes such as calble laying and expansion of waterways. The electric resistivity is a key parameter for addressing sediment types. We developed a measuring technology based on a geoelectrical streamer for near-coast application (see technical development). Through cooperation with the University of Greifswald several profiles could be already measured and interpreted using modern algorithms.

Soil probing in precision farming using rolling electrodes

The identification of soil types and their layering is important for modern precision agriculture. The electric conductivity plays again a key role. In order to investigate large areas in adequate times, the Leibniz-Institute for Agricultural Engineering in Potsdam-Bornim developed a mobile carrier using rolling electrodes. The measurements can be used to compute a three-dimensional model using fast and robust algorithms.

Transient Electromagnetics (TEM)

Transient electromagnetic (TEM) measurements provide information on the distribution of the electrical conductivity, or its reciprocal electrical resistivity, of the subsurface. The measurements yield the apparent resistivity and after a 1-dimensional data inversion one obtains the true resistivity distribution for a layered earth model. 
The TEM method uses transmitter and receiver coils with different sizes and configurations. A primary signal is produced by a current shut-off in the transmitter coil. A decaying voltage curve in the receiver coil, generated by the diffusing eddy current system in the ground, is recorded over a certain time window. The resulting exploration depth depends only on the local noise level. By varying coil size and time window the TEM system is able to provide information on the resistivities of layers at greater depths below surface. TEM measurements can be performed along several profile lines across the areas of interest and at single sites. Detailed information can be retrieved from the BGR website on TEM.

Ground penetrating radar (GPR)

GPR is a fast technique for investigating the near surface with a high spatial resolution. It is commonly used for a structural determination, e.g. of costal sediments, peat layers or salt deposits or to detect buried archaeological objects and landmines. Further on, physical properties can be deduced as e.g. moisture or clay content of soils which are important factors for solving hydrological or agricultural problems. Details

Investigations in Salt Deposits
The aim of the joint research project which is funded by the BMBF is to methodically enhance geophysical techniques for reconnaissance studies in salt deposits. A further objective is to develop a tool for a combined interpretation of the measured data. The subject of study is the geological barrier of subsurface waste disposals and to detect possible critical zones as e.g. brine occurrences. The responsibility of the LIAG Institute are the sub-projects ground-penetrating radar, electromagnetic induction and qualitative characterisation.

Humanitarian Demining
Metal detectors are commonly used for landmine detection. Recently, ground-penetrating radar has also been introduced for this purpose. Both techniques are often negatively influenced by the soil. The aim of the project which is funded by the BMVg is to quantitatively describe the relevant physical soil properties and to analyse their influence on landmine detection.

Investigations in the Cuxhaven area

Multielectrode resistivity measurements are a modern and powerful instrument for mapping near surface structures. Within the scope of the PhD thesis Mohammed Attwa investigates whether it can be applied for detection of local structures in the marsh land near Cuxhaven, e.g. clay distribution or small-scaled buried valleys. Systematic model studies and electromagnetic measurements have been recently done. Furthermore, two Diploma students carry out additional resistivity profiles. Details