There are many migration algorithms that can be used for velocity estimation. Fowler 1988 used time migration, Al-Yahya 1987 used shot-profile migration, and Etgen 1990 used common-offset migration. The plane-wave synthesis imaging can be considered as a migration algorithm that takes advantages of both shot-profile and common-offset migration algorithm. In terms of accuracy, it is comparable to shot-profile migration that is known as the most accurate algorithm because it utilizes wave equation for wavefield extrapolation. In terms of efficiency, it is comparable to the common-offset imaging that produces a global subsurface image for each common-offset image section, unlike the shot-profile imaging, which produces a local image for each shot-profile image.

In addition to the favorable aspects as given above, the PWS imaging has an advantage in that it contains information about local ray trajectories on the datum where the wavefront was synthesized. This information about the ray path is not available in the algorithm that is based on the wavefield extrapolation, unless a ray tracing is additionally applied. This property motivates the development of a tomographic velocity estimation using the PWS imaging presented in this thesis.

Another advantage of the PWS imaging is the imaging condition. There are several imaging algorithms that can be used for angle-dependent reflectivity recovery. De Bruin et al. 1990 used shot-profile migration with imaging in the Fourier domain and Cunha Filho 1992 uses the reverse-time migration with a local plane-wave-response imaging condition. Even though those methods apply the theoretically correct imaging condition, those are not practical to implement because the method of imaging in the Fourier domain requires spatial invariance of the reflectivity and the method using reverse-time migration requires to save wavefields for all the extrapolation time steps before imaging. However, the PWS imaging condition implicitly uses the same imaging condition as those and is easily applicable to a general case such as a non-flat reflector in a laterally-varying velocity medium.

2/5/2001