Inversion gradients for acoustic VTI wavefield tomography

Inversion gradients for acoustic VTI wavefield tomography

Vladimir Li, Hui Wang, Ilya Tsvankin, Esteban Díaz and Tariq Alkhalifah, ”Inversion gradients for acoustic VTI wavefield tomography” Geophysics 82 (2017): WA55-WA65. doi: 10.1190/geo2016-0624.1
BibTeX​ 
Vladimir Li, Hui Wang, Ilya Tsvankin, Esteban Díaz, Tariq Alkhalifah
wavefield tomography, imaging, transverse isotropy, acoustic, inversion
2017
​Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a generalized pseudospectral operator based on a separable approximation for the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified image-power objective functions. We also obtain the gradient expressions for a data-domain objective function that can more easily incorporate borehole information necessary for stable VTI velocity analysis. These gradients are similar to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations but the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show the potential advantages of the modified image-power objective function in estimating the anellipticity parameter ηη.
(print): 0016-8033 (online): 1942-2156