DMO and coherent linear noise
The constant-velocity assumption underlying the most commonly used DMO algorithms can sometimes attenuate dipping events. This is the case with a shallow dipping event and a deep flat event . If velocity increases with depth (the usual case), then these two events can arrive about the same time and have similar moveouts (Figure 5.2-27). In terms of velocities, this implies that the moveout (or stacking) velocity v1/cos θ for the shallow, dipping reflector is approximately equal to the moveout velocity v2 associated with the deep, flat reflector. Following the DMO correction, nothing happens to the flat event, while the dipping event shifts to a lower velocity value v1. The dipping event, that may be associated with coherent linear noise, drifts away from the velocity function for flat events and thus is attenuated during stacking.
This characteristic response of DMO can be used to our advantage in attenuating coherent linear noise associated with shallow point scatterers in the water bottom. A field data example is shown in Figure 5.2-28. While the diffractions associated with the steep flanks of the salt diapir are better preserved by DMO correction, the steep coherent linear noise is attenuated by this process.
Figure 5.2-28 A portion of a CMP stack, (a) without, and (b) with DMO correction. Note the attenuation of coherent linear noise by DMO correction.
- Black et al., 1985, Black, J.L., McMahon, I.T., Meinardus, H., and Henderson, I., 1985, Applications of prestack migration and dip moveout: Presented at the 55th Ann. Internat. Mtg., Soc. Expl. Geophys.
- Salt flanks
- Fault planes
- DMO and multiples
- Other considerations
- Aspects of DMO correction — a summary