DIELECTRIC PROFILING OF ALPINE ICE CORES AS ASSISTANCE FOR GROUND PENETRATING RADAR

• Main Author: Hackel, Martin
• Format: Thesis
• Language: unknown
• Published: 2013
• Subjects: Mont Blanc; Monte Rosa; ice core
• Online Access: https://epic.awi.de/id/eprint/43439/; https://epic.awi.de/id/eprint/43439/1/Hackel_Diplomarbeit_2013-DEP-GPR-Colle.pdf; https://hdl.handle.net/10013/epic.49849; https://hdl.handle.net/10013/epic.49849.d001

The present thesis aimed to, for the first, deploy dielectric profiling (DEP) to an entire Alpine ice core drilled to bedrock. DEP allows for a non-destructive measurement of an ice core’s complex relative dielectric permittivity at kHz frequencies. Based on the thus obtained dielectric profile of the core, it was the task to derive a synthetic radargramm by forward modelling and to compare the later with radar traces from ground penetrating radar (GPR). Forward modelling by convolution of the reflectance profile, derived from DEP data, with a synthetic radar wavelet in the time domain yields a synthetic radargramm, which in principle should reproduce the coherent features of a GPR trace recorded adjacent to the borehole. Thereby a physical connection between ice core properties and radar reflectors is established. The method was applied in full extent to the CDM core from Col du Dôme (CDD), Mont Blanc, and partially to the KCC core from Colle Gnifetti (CG), Monte Rosa, which supplemented the thesis in it’s final stage. The DEP data of the CDM core was afflicted with a comparatively large amount of defects and with artefacts due to a dysfunction of the DEP setup. An adequate approach of data treatment was rigorously developed and applied. The corrections could be assessed with the complementary data of the KCC core. Analysis of the DEP profiles e.g probably allowed the identification of a known regime change in Alpine snow chemistry in the 1950s. Forward modelling reproduced in the firn part several reflectors from GPR traces adjacent to the borehole predominately caused by permittivity changes. As by product the analysis of radargramms from CDD revealed below the firn-ice transition a reflector-free zone (RFZ), as it is known from CG, and offered some indications regarding its origin.