Least-squares reverse time migration for the Cascadia ocean-bottom dataset

Higher order mirror imaging

To image with higher-order multiples, we need to construct a migration operator that can account for the kinematics of the appropriate wave paths. To simulate the final down-going leg of the wave path, an areal shot is pre-calculated by first injecting the source wavelet at the receiver location, letting the wavefield propagate, and then capturing the signal at the sea surface (Figure 3). To generate the incident wavefield, the saved areal shot is re-injected at the sea-surface with a -1 factor. The re-injected signal is then allowed to travel back and forth in the water column using a reflecting top boundary and a well-defined velocity contrast at the sea-bottom. This algorithm can correctly simulate the wave paths traversed by the mirror signal, the double-mirror signal and even higher-order multiples.

Figure3
Figure 3. Illustration for the migration of the double-mirror signal. For the incident wavefield, an areal shot is pre-calculated to simulate the final down-going leg of the wave path. To generate the incident wavefield, the saved areal shot is re-injected at the sea-surface with a -1 factor. The re-injected signal is then allowed to travel back and forth in the water column using a reflecting top boundary and a well-defined velocity contrast at the sea-bottom.

Note that this technique does not migrate all orders of multiples. It only migrates surface-related multiples with a single reflection in the reflectivity model or with reflections in the acoustic modeling based on a sharp boundary in the velocity model.

Least-squares reverse time migration for the Cascadia ocean-bottom dataset