In recent years, wave-equation imaged data are often presented in common-image angle-domain gathers as a decomposition in scattering
angle at the reflector, which provide a natural access to analyzing
migration velocities and amplitudes. In the case of anisotropic
media, the importance of angle gathers is enhanced by the need to
properly estimate multiple anisotropic parameters for a proper
representation of the medium. We extract angle gathers for each
downward-continuation step from converting offset-frequency
planes into angle-frequency planes simultaneously with applying the
imaging condition in a transversely isotropic 2with a vertical symmetry axis (VTI) medium. The
analytic equations, though cumbersome, are exact within the
framework of the acoustic approximation. They are also easily
programmable and show that angle gather mapping in the case of
anisotropic media differs from its isotropic counterpart, with the difference
depending mainly on the strength of anisotropy. Synthetic examples demonstrate
the importance of including anisotropy in the angle gather generation as mapping of
the energy is negatively altered otherwise. In the case of a titled axis of symmetry (TTI),
the same VTI formulation is applicable but requires a rotation
of the wavenumbers.
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