Characterisation of high-frequency electromagnetic properties of soils and sediments in the lab. These investigations serve as basis for the simulation of EM wave propagation and for a fundamental understanding of polarisation mechanisms in the subsurface
The propagation of electromagnetic waves in the radar frequency range is influenced by the dielectric soil properties. Due to the superposition of several relaxation processes in the soil, these properties exhibit a frequency-dependence. The knowledge on the relaxation behaviour of soils is important for the interpretation of radar signatures and ,e.g., to deduce water contents from GPR data. In addition, frequency-dependent dielectric properties are an important imput parameter for realistics simulation of wave propagation.
Using a high-frequency measuring device, soil samples are inserted into a measuring cell as part of a coaxial transmission line and can be analysed under controlled conditions (e.g., water content and temperature). A network analyser is used to measure the coefficient of reflection and transmission of the cell over a broad frequency range. From this data the spectrum of the complex dielectric permittivity is deduced.
Until now, more than 100 different soils and sediments have been analysed at various water contents and the results are stored in a data base. To some extent, the HF data have been complemented by LF SIP (spectral induced polarisation) measurements and petrophysical models were fitted, which describe the whole frequency range of electromagnetic methods (mHz – GHz range). The data base is a helpful input for the simulation of frequency dependent electromagnetic wave propagation.