Retrieving the propagation velocity of electromagnetic waves in a two-layered medium through diffraction curves

This paper addresses the problem of retrieving the propagation velocities of electromagnetic waves in a non-homogeneous soil made up of two layers sep- arated by a not-flat interface. The propagation velocities are estimated from GPR data gathered at the air–soil interface in common offset configuration. The well- known diffraction hyperbola method is exploited for retrieving the propagation velocity in the shallower layer. Conversely, an extension of the diffraction hyper- bola method is proposed to estimate the propagation velocity in the second layer (meant as the deeper one). The proposed approach accounts numeri- cally for the refraction of the waves at the buried interface, which deforms the diffraction curve. The shape of the buried interface is accounted for by using abscissa-time samples picked up from the data. The approach exploits theoreti- cal aspects derived for a flat buried interface and empirically extends them to the case of a curved (smooth) buried interface. Experimental results in a controlled scenario are presented.