Vector wavefields are commonly reduced to their scalar eigenfields. This procedure reduces the data volume of multicomponent source and multicomponent receiver data into a more manageable size. After conversion to scalar fields, conventional processing techniques can be applied (Nichols, 1990). Most conventional techniques assume isotropic wave propagation. It is generally observed that NMO and vertical propagation velocities in conventional seismics do not coincide. This presents a problem when an attempt is made to properly image the subsurface: which migration velocity should be used? If the NMO velocity is used, diffractions will be focused quite well but that focus will be misplaced. If the vertical propagation velocity is used, diffractions will not collapse properly. This situation calls for the application of anisotropic imaging techniques, as shown in this paper.
Whether it is easy to include anisotropy, in the form of the exact dispersion relation, in existing conventional algorithms, depends largely upon whether the methods are implemented in the phase or group domain. In the anisotropic world, there is no easy way to go from the phase to the group domain and vice versa. However, if the double elliptic approximation is used, the two domains can be described by the same set of parameters and conversion between them is easy.