Wavefield tomography and waveform inversion are related techniques that share the need to simulate accurate wavefields in the subsurface. In both cases, models are updated iteratively using gradients computed by, for example, the adjoint state method. The major difference between these techniques is the domain in which one formulates the objective function that compares the observed and simulated wavefields. For image-domain wavefield tomography, the objective function is defined based on a residual evaluated using migrated images. The role of the penalty function is to highlight image defocusing caused by imperfect velocity. This is accomplished by defining an operator which annihilates an image corresponding to the correct velocity. Conventional techniques, like differential semblance optimization, assume that correctly migrated images are completely focused, which is not the case when illumination is poor. In this paper, we address this problem by defining an alternative penalty operator which takes illumination into consideration and leads to more robust and accurate inversion results. This technique is particularly relevant for imaging in complex areas, e.g. sub-salt.


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