Simple L Model

The L model in Figure (a) is sampled with a grid size of $301 \times 601$ points, and a grid interval of 10 m. There are 31 shots evenly distributed along the $x$ -axis at a 10 m depth with a 200 m shot interval. Every shot is recorded with the same 601 receivers at a 10 m depth with a 10 m receiver interval for a fixed spread acquisition geometry. Figure  plots a shot gather with the source at $x=4.6~km$ , which clearly shows the direct waves, the diffractions from the top of the vertical reflector, the reflections off the horizontal reflector, and the prism waves are marked by a yellow arrow.

The 31 shot gathers are first migrated with a homogeneous velocity model ($2~km/s$ ) by a conventional RTM method, and the image is shown in Figure (a), where only the horizontal reflector is visible. Then the proposed prism wave RTM algorithm is applied to the same 31 shot gathers with the same homogeneous velocity and the RTM image (Figure (a)) to give the image in Figure (b), which clearly depicts the vertical reflector. The horizontal reflector acts as the location of secondary sources during the migration process, which appears in the Figure (b) image.

Figure: A shot gather with the source at $x=4.6~km$ . The shot gather contains the direct wave, the reflection off the horizontal reflector, and the diffraction from the top of the vertical reflector. The yellow arrow points out the prism wave.

Figure 4.8: (a) The RTM image obtained with a homogeneous velocity model. The vertical reflector is not illuminated. (b) The RTM image of the prism waves with homogeneous velocity and the reflectivity image in panel (a). The vertical reflector is well imaged.