Application of 2D (visco)-elastic Rayleigh Waveform Inversion to Ultrasonic Data from the Porta Nigra in Trier (Germany)

Beside geophysical applications from the near-surface to global scale, seismic full waveform inversion (FWI) can be applied to ultrasonic data on the centimeter and decimeter scale for non-destructive testing (NDT) of pavements, facades, plaster, sculptures and load-bearing structures like pillars. Classical NDT approaches are based on the inversion of body-wave travel-times to deduce P-wave velocity models. In contrast, surface waves (Rayleigh or Love waves) are well suited to quantify superficial alterations of material properties, e.g. due to weathering. In this paper we demonstrate the potential of 2D Rayleigh waveform inversion on the ultrasonic scale using a very low coverage acquisition geometry consisting of 1 shot and a few dozen receiver positions. For a 2D elastic FWI with a passive visco-elastic modelling approach the resolution is illustrated using a ultrasonic field data example from the weathered facade of the Porta Nigra, a large Roman city gate from the 2nd century AD, in Trier (Germany).