Plane-wave Prestack LSRTM

When all 31 plane-wave gathers are migrated by conventional RTM and the migration images are stacked together, the final image is of higher quality than Figure (a) due to the stacking process. Figure (a) shows the stacked plane-wave RTM image after high-pass filtering. Compared to shot-domain RTM image in Figure , there are fewer artifacts in the shallow part and the reflector amplitudes are more balanced in the deep part. There are also some migration artifacts that are related to the strong diffractors.

Figure 3.6: (a) The plane-wave RTM image of the Marmousi2 model and (b) plane-wave LSRTM image of the Marmousi2 model after 30 iterations. All the 31 plane-wave gathers are used.

In the next step, the 31 plane-wave gathers are migrated with the numerical scheme in equation and Figure (b) shows the plane-wave LSRTM image after 30 iterations, which is of much higher quality when compared to Figures  and (a) in terms of resolution. Also, the migration artifacts are less noticeable in the LSRTM image, and the reflector amplitudes are nearly the same from shallow to deep depths. With the prestack images, the common image gathers (CIGs) can be extracted from the plane-wave RTM and LSRTM images.

Figure  shows the common image gathers from the RTM image, where it is obvious that the migration velocity is accurate since all the image gathers are flat. Strong low-wavenumber artifacts can be seen, which are expected to be the RTM artifacts (Liu et al., 2011). There is some coherent noise present in the gathers, which can be related to internal multiples. With an increasing number of iterations, the quality of CIGs is improved, as shown in Figure . The low-wavenumber artifacts are mostly removed in the CIGs from the LSRTM image. However, in the complex region of the model (faults), some steeply-dipping coherent noise is preserved during the iterations of LSM.

Figure 3.7: The common image gathers extracted from the plane-wave RTM image.

Figure 3.8: The common image gathers extracted from the plane-wave LSRTM image after 30 iterations.