Integration of georradar methods and electromagnetic induction for caves mapping: application to sono cave - Arrábida

Abstract

This paper presents the results of the geophysical survey to mapping a section of the “Lapa do sono” cave, situated in Serra da Arrábida (Sesimbra), which is known to have had funerary occupation in the old Neolithic Age. Nowadays this cave finds itself widely obstructed by sediments, whose extension we intent know. Two technics frequently used in the subsurface prospection in an archaeologic environment were chosen, the Ground Penetrating Radar (GPR) and the low-frequency electromagnetic induction (EM). Due to the difficult terrain circulation state, which cannot be improved due the restrictions imposed by the nature protection defence, the data acquisition was made according an unusual paradigm. The methodology followed had based on an exhaustive analysis about a limited number of modelling profiles, using a distinct 2D processing methods. The results allow to outline the sector A of the cave inserted in a karst environment, widely fragmented, mainly on the cavity coverage areas. Evidences of other minor cavities adjacent to the main cave have also been collected; these cavities may be connected to the grotto through minor galleries filled with sediments. The interpretation of the results allowed the evaluation of the sediments thickness accumulated on the grotto surrounding’s, under the sampled profiles.