Student projects

The mineral-magnetic compositions of sand samples collected along the Pacific coast of Namibia and Angola will be investigated by hysteresis and susceptibility measurements between room temperature and 700°C. The thermal variation of the magnetic pattern of the samples provides information about the magnetic carriers and their source areas. Knowing the source areas is a key to deduce eolian transport mechanism during desertification. In combination with published climate information these data will be used to reconstruct the development of the Namibian Sand Sea since early Miocene. This project addresses students with interests in geophysical experiments in the context of the broad field of landscape development.

Contact: Dr. Andreas Gehring

The evolution of the geomagnetic field, both in direction and intensity, is important when studying geodynamics. Whereas directional information can be obtained easily from a stably magnetized rock, retrieving paleointensity is more complicated. Remanent magnetization is carried by ferromagnetic minerals as for example magnetite. If magnetite undergoes chemical alteration, its magnetization changes and it can no longer be used for paleointensity studies. Therefore, it is preferred to investigate ferromagnetic inclusions in single crystals that are protected against environmental influences by the surrounding silicate lattice. However, these inclusions normally have preferential orientation within the single crystal, which might cause anisotropy in the remanent magnetization. This study will investigate the orientation of ferromagnetic inclusions in single crystals and how this affects the remanent magnetization.

Contact: Prof. Ann Hirt

Agriculture is the main national cause of ammonia emission. The largest part of emission arises during the broad-spreading of slurry. With band-spreading methods the emission can be reduced by half in comparison to broad-spreading. The Swiss government supports farmers to use band-spreading application techniques. This technique concentrates the solid parts of slurry on small lines on the farmland. Farmers, however, fear that this concentration can lead to a contamination of growing grass, which will be harvested, such that solid parts of the applied slurry will still be found in harvested food.
Argroscope Reckenholz-Tänikon (ART) runs a project in which three different application techniques are compared. Differences in N efficiency, and changes in botanical and food quality are the focus of this study.
The project investigates the use of magnetic parameters to detect any slurry remaining in harvested grass.

Contact: Prof. Ann Hirt, Joachim Sauter (Argroscope Reckenholz-Tänikon)

A number of new algorithms have presented themselves that are able to solve inverse problems by variations on random walk or Monte Carlo approaches. Two such algorithms are in everyday use in electromagnetic induction and in seismology. We plan to study their applicability to inverse problems in general, but will begin on an inverse problem with only three dimensions, in order to compare performance.

This parameter estimation problem is concerned with retrieval of principle absorbances of a crystal species using infra-red spectroscopy, and is one of the few inverse problems that is truly finite-dimensional. Algorithms that present themselves as general parameter-space sampling methods include the Neighbourhood Algorithm of Sambridge, the Covariance Matrix Adaption Evolution Strategy (CMAES) and various flavours of MCMC including Hamiltonian Monte-Carlo.

The ``no free lunch theorem’’ suggests that there is no general algorithm that is able to solve a variety of problems. Despite that, it may be
possible to draw some conclusions regarding the applicability of various algorithms to typical geophysical inverse problems arising in seismology,  electromagnetic induction and geomagnetism.

The topic will be of interest to students with a good background and interest in mathematics and probability, together with good computing skills.

Contact: Prof. Andrew Jackson, Prof. Alexander Grayver, Prof. Andreas Fichtner