“…In literature, two approaches can be basically found: inversion techniques mostly based on approximated solutions of the scattering integral equation (Joachimovicz et al, 1991;Caorsi et al, 1993;Pierri et al, 2002;Lambot et al, 2004; Correspondence to: S. Caorsi (salvatore.caorsi@unipv.it) Kao et al, 2007) or "learning by examples" procedures employing artificial neural networks (Hoole, 1993;Caorsi and Gamba, 1999;Youn and Chen, 2003;Caorsi and Cevini, 2005a). The former approach, generally more precise and widely applicable, suffers high computational costs, and machine learning algorithms are now becoming powerful alternatives.…”