An extension of the diffraction hyperbola method to layered media

The stratigraphy of urban sub-soils is commonly quite complex and the effective use of GPR technology requires a modelling of the signal propagation as occurring into a layered structure, often made up by not flat interfaces, rather than into a homogeneous medium. Accordingly, the estimate of the signal velocity into different materials needs to be accurate, because it affects both the focusing and the positioning of the buried targets [1-2]. In this framework, we propose an extension of the diffraction hyperbola method as effective tool for retrieving the propagation velocity of the electromagnetic waves in layered media [3]. In particular, we will consider a stratified soil with two layers whose separating interface is not flat. In this case, the diffraction curves are deformed by the refraction of the waves at the buried interface and no analytic formula for the scattering is available. We demonstrate that a suitable numerical forward modelling performed with the help of the gprMax software [4] can help retrieving the value of the propagation velocity in the second layer. At the conference we will show that, if properly dealt with, the diffraction curves generated by electrically small targets can still provide information about the properties of the soil, even if the reflection at the interface makes more difficult and trickier to look into the second layer. The method can be theoretically extended to a generic number of layers, but the possibility to effectively investigate targets in the third layer (or in layers following the third one) becomes practically feasible only if the reflection at the interfaces is weak, i.e. only if the electromagnetic characteristics of the subsequent adjacent layers are quite similar to each other. Key words: Layered media, propagation velocityReferences[1] R. Pierri, G. Leone, F. Soldovieri, R. Persico, "Electromagnetic inversion for subsurface applications under the distorted Born approximation" Nuovo Cimento, vol. 24C, N. 2, pp 245-261, March-April 2001.[2] I. Catapano, L. Crocco, R. Persico, M. Pieraccini, F. Soldovieri, “Linear and Nonlinear Microwave Tomography Approaches for Subsurface Prospecting: Validation on Real Data”, IEEE Trans. on Antennas and Wireless Propagation Letters, vol. 5, pp. 49-53, 2006.[3] R. Persico G. Leucci, L. Matera, L. De Giorgi, F. Soldovieri, A. Cataldo, G. Cannazza, E. De Benedetto, Effect of the height of the observation line on the diffraction curve in GPR prospecting, Near Surface Geophysics, Vol. 13, n. 3, pp. 243-252, 2014.[4] C. Warren, A. Giannopoulos, I Giannakis, gprMax: Open source software to simulate electromagnetic wave propagation for Ground Penetrating Radar, Computer Physics Communications, 209, 163-170, 2016 10.1016/j.cpc.2016.08.020.

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