GEODYNAMICS

Abstract

The purpose of the research was to verify the extraordinary big theoretical penetration depth of new developed georadar in the real conditions of karsts areas. The new kind of the Ground Penetrating Radar (GPR) – Roteg – was developed in 2013 (RTG-Tengler 2013). Its technical parameters (pulse peak on the transmitting antenna 20 kV or more, and the sensitivity of the receiving antenna at least 2 uV, i.e. the real signal detection level around 20 uV) express that the real signal detection sensitivity is 9 orders, i.e. 180 dB. Such sensitivity means that the real penetration depth should be two orders bigger than in the case of common GPR´s. We tested the real penetration depths in the suitable environmental conditions over the caves in the Moravian Karst and in Slovenia near Postojna cave. The measurements results showed that reflections from known caves are reliably detectable at depths of 40-210 m below the surface. Reflections from the geological structures up to a depth of 480 m, in which the bottom of Lift II is probably located, were observable on the profile above the Hranická abyss. The new kind of Roteg georadar with 20 kV pulses on the transmitting antennas was able to detect reflections from the Devon – Brno Granite contact at a depth of up to 850 m in the case of optimal conditions in the karst without soil cover (in the Malá Dohoda quarry in the Moravian Karst). The radarogram showed a change in the lithology between the Vilémovice – Lažánky limestone and layers of clasts in the bottom of limestone strata. Both of the tests mentioned above confirmed the extraordinary big penetration depth of the GPR signal which exceeded 500 m in karst conditions when using the maximum power on transmitting antennas. The quite new kind of GPR called Roteg with the extraordinary high voltage on transmitting antenna and pulse instead of harmonic signal generation of transmitted signal allows reach two orders bigger penetration depths than the common GPRs.. The new kind of Roteg GPR makes it possible to obtain data (especially from karst areas) from depths that were previously only accessible by seismic methods or boreholes. GPR measurements are orders of magnitude cheaper and much faster in the field.