On attenuation-matched inversion methods of diffusive wavefields

The non-destructive evaluation of a defect affecting a metal half-space fro m the observation of electromagnetic diffusive wavefields observed from abo ve in air is considered within a linearizing assumption of the wave phenome non. Emphasis is on appropriately solving a coupled Fourier-Laplace transfo rm in order to map the conductivity contrast of the damaged block. To do so , two related 'optimal' solution methods are developed. The first one makes use of an exponential sampling both of the observation frequency bandwidth and of the depth extent of the search domain, and the second is based on a n appropriate calculation of a weighted generalized solution. Synthetic res ults illustrate the features of these two solution methods for a variety of defect configurations, in particular they show that support information ac quired in an iterative fashion allows zooming onto the defect. Comparisons with known diffraction tomographic schemes are also carried out. Extensions of the solution methods are proposed and the fact that nonlinearized inver sion schemes may benefit from a sampling matched to the attenuation is unde rlined.