Radio Echo-Sounding (RES) is an active remote sensing technique. The physical basis is the transmission of an electromagnetic pulse (EMP) via an antenna, located above the medium of interest, in our case the glacier ice. The pulse penetrates the ice and is partly reflected at inhomogenities. The reflections are received at the surface via a second antenna. The analysis of the recorded signals provides information on the physical and chemcal properties of the ice.

Three processes are known to cause internal reflections: changes in density (e.g. ice or hoar layers in the firn), changes in chemical properties (e.g. volcanic acids) and changes in the crystal orientation fabrics.

To get quantitative insights into the physical processes leading to radar reflections, we use high resolution records of the dielectrical properties of ice cores to perform numerical modeling experiments. With the use of a finite-difference (FD) time domain (TD) model, it is possible to simulate the propagation of an EMP in ice and to investigate the influence of certain structures on the propagation. With this technique we were able to identify a number of internal layers that originate from horizons made up of volcanic acid and separate them from those caused by changes in crystal orientation fabrics.