Simulated reflection versus migration

In this section, we present some numerical results showing the behavior of the simulated reflection shot gathers and the migrated image when changing some source and receiver parameters. The migrations were performed with the exact velocity model. No multiple elimination schemes were applied.

The quality of the end result depends strongly on the number of the present subsurface sources. The left panels from Figures 3 through 6 show simulated reflection shot gathers for a decreasing number of subsurface noise sources with a simulated surface shot position at x₁=4000 m. The right panels from Figures 3 through 6 show the results from direct migration of the same noise recordings. The noise recordings were 6 minutes long. We see that the simulated reflection responses very quickly decrease in quality (compared with the directly modelled reflection response in Figure 11), while the migration process delivers much better results. Fewer source locations cause illumination problems in the migration result.

 

dx_50m
Figure 2 Left: Simulated reflection shot panel from 6 minutes long noise recordings with 113 regularly distributed subsurface sources with a simulated shot position at x₁=4000 m. Right: Result from direct migration of 6 minutes long noise recordings with 113 regularly distributed subsurface sources.

The left panels of Figures 7 through 10 show the change in quality of the simulated reflection shot gather (with simulated surface shot position at x₁=4000 m) when decreasing the recording time length of the receivers. The right panels of Figures 7 through 10 show the migrated image for the same noise recordings. We can see that while for short recording times the quality of the simulated reflection is strongly degraded, the result from migration is still good, only the signal-to-noise ratio has decreased. Note that multiple events that are hardly visible in the simulated reflection shot gathers at short recording times are still clearly present in the migrated image.