Linear and nonlinear inversion algorithms applied in nondestructive evaluation

Abstract

Convenient tools for nondestructive evaluation of solids can be electromagnetic and/or elastodynamic waves; since their governing equations, including acoustics, exhibit strong structural similarities, the same inversion concepts apply. In particular, the heuristic SAFT algorithm (synthetic aperture focusing technique) can be-and has been-utilized for all kinds of waves, once a scalar approximation can be justified. Relating SAFT to inverse scattering in terms of diffraction tomography, it turns out that linearization is the most stringent inherent approximation. Hence, the results of nonlinear inversion schemes such as contrast source inversion are compared to the output of SAFT for a carefully designed ultrasonic experiment. In addition, it will be shown via synthetic as well as experimental data that SAFT can be extended to electromagnetic vector fields and to an inhomogeneous and/or anisotropic background material.

Interferometric array imaging in clutter

“…The result is 38) where the extra factors of z in the amplitude are due to the integration. We can write (5.38) in a simpler form that makes the resolution of the coherent interferometric point spread function I CINT ( y s ) more transparent.…”

Structural Assessment via Ground Penetrating Radar at the Consoli Palace of Gubbio (Italy)

“…Indeed, a radargram provides a distorted image of the scenario under test, which can lead to incorrect readings of the information gathered. As a consequence, there is a continuing interest in the development and use of application-oriented data-processing approaches capable of providing easily interpretable images [2][3][4]6,[13][14][15][16][17][18][19].…”

Ground Penetrating Radar Subsurface Imaging of Buried Objects

“…Eq. (5) allows us to point out the equivalence between the Diffraction Summation and the Range Migration Technique presented in (Lopez-Sanchez & FortunyGuasch, 2000) and also to the Synthetic Aperture Focusing Technique (SAFT) (Markelein et al, 2002). As can be seen, these methods are essentially based on a convolution in O x and an integration in k .…”