Geophysical cave detection with a portable Very Low Frequency (VLF) radio transmitter

(1) RWTH Aachen University, Applied Geophysics and Geothermal Energy, Aachen, Germany (fbosch@eonerc.rwth-aachen.de), (2) University of Cologne, Institute of Geophysics and Meteorology, Cologne, Germany (geogurk@geo.uni-koeln.de), (3) Swiss Institute of Speleology and Karst-Research (SISKA), La Chaux-de-Fonds, Switzerland (info@isska.ch), (4) University of Neuchâtel, Institute of Geology and Hydrogeology, Centre of Hydrogeology and Geothermics (CHYN), Neuchâtel, Switzerland (imre.muller@unine.ch)