scholarly journals Quantitative mapping of thickness variations along a ray path using geometrical full waveform inversion and guided wave mode conversion

2022 ◽  
Vol 478 (2257) ◽  
Author(s):  
Peng Zuo ◽  
Peter Huthwaite
Keyword(s):  
Guided Waves ◽  
Mode Conversion ◽  
Waveform Inversion ◽  
Guided Wave ◽  
Direct Access ◽  
Thickness Variation ◽  
Full Waveform Inversion ◽  
Large Area ◽  
Wave Inversion ◽  
Full Waveform

Quantitative guided wave thickness mapping in plate-like structures and pipelines is of significant importance for the petrochemical industry to accurately estimate the minimum remaining wall thickness in the presence of corrosion, as guided waves can inspect a large area without needing direct access. Although a number of inverse algorithms have been studied and implemented in guided wave reconstruction, a primary assumption is widely used: the three-dimensional guided wave inversion of thickness is simplified as a two-dimensional acoustic wave inversion of velocity, with the dispersive nature of the waves linking thickness to velocity. This assumption considerably simplifies the inversion procedure; however, it makes it impossible to account for mode conversion. In reality, mode conversion is quite common in guided wave scattering with asymmetric wall loss, and compared with non-converted guided wave modes, converted modes may provide greater access to valuable information about the thickness variation, which, if exploited, could lead to improved performance. Geometrical full waveform inversion (GFWI) is an ideal tool for this, since it can account for mode conversion. In this paper, quantitative thickness reconstruction based on GFWI is developed in a plate cross-section and applied to study the performance of thickness reconstruction using mode conversion.

scholarly journals On cycle-skipping and misfit functions modification for full-wave inversion: comparison of five recent approaches

Geophysics ◽  
2021 ◽  
pp. 1-85
Author(s):  
Arnaud Pladys ◽  
Romain Brossier ◽  
Yubing Li ◽  
Ludovic Métivier
Keyword(s):  
Least Squares ◽  
Field Data ◽  
Optimal Transport ◽  
Waveform Inversion ◽  
Imaging Method ◽  
Full Waveform Inversion ◽  
Wave Inversion ◽  
Full Waveform ◽  
Full Wave ◽  
Definition Of

Full waveform inversion, a high-resolution seismic imaging method, is known to require sufficiently accurate initial models to converge toward meaningful estimations of the subsurface mechanical properties. This limitation is due to the non-convexity of the least-squares distance with respect to kinematic mismatch. We propose a comparison of five misfit functions promoted recently to mitigate this issue: adaptive waveform inversion, instantaneous envelope, normalized integration, and two methods based on optimal transport. We explain which principles these methods are based on and illustrate how they are designed to better handle kinematic mismatch than a least-squares misfit function. By doing so, we can exhibit specific limitations of these methods in canonical cases. We further assess the interest of these five approaches for application to field data based on a synthetic Marmousi case study. We illustrate how adaptive waveform inversion and the two methods based on optimal transport possess interesting properties, making them appealing strategies applicable to field data. Another outcome is the definition of generic tools to compare misfit functions for full-waveform inversion.

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