“…From a mathematical viewpoint, subsurface imaging is a special case of inverse scattering problem where, at microwave and radio-frequencies, targets are reconstructed in terms of a spatial map of their electromagnetic features, usually given in terms of dielectric permittivity [10,11], electrical conductivity and, recently, magnetic permeability [12]. Inverse scattering problems are non-linear and illposed [8,9] and their solution under an exact formulation generally requires to set up some optimisation procedure (either deterministic or stochastic) [10, 13 -15].…”