TIME- VERSUS FREQUENCY-DOMAIN INVERSE ELASTIC SCATTERING: THEORY AND EXPERIMENT

This study formally adapts the time-domain linear sampling method (TLSM) for ultrasonic imaging of stationary and evolving fractures in safety-critical components. The TLSM indicator is then applied to the laboratory test data of [F. Pourahmadian and H. Yue, Inverse Problems, 37 (2021), 055012; F. Pourahmadian, Mech. Syst. Signal Process., 161 (2021), 108029] and the obtained reconstructions are compared to their frequency-domain counterparts. The results highlight the unique capability of the time-domain imaging functional for high-fidelity tracking of evolving damage, and its relative robustness to sparse and reduced-aperture data at moderate noise levels. A comparative analysis of the TLSM images against the multifrequency LSM maps of [F. Pourahmadian and H. Yue, Inverse Problems, 37 (2021), 055012] further reveals that thanks to the full-waveform inversion in time and space, the TLSM generates images of remarkably higher quality with the same dataset.