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Reverse-time migration

Reverse-time migration reconstructs the source wavefield forward in time and the receiver wavefield backward in time. It then applies an imaging condition to extract reflectivity information out of the reconstructed wavefields. The advantages of reverse-time migration over other depth migration techniques are that the extrapolation in time does not involve evanescent energy, and no dip limitations exist for the imaged structures  (Whitmore, 1983; Baysal et al., 1983; McMechan, 1983,1982). Although conceptually simple, reverse-time migration has not been used extensively in practice due to its high computational cost. However, the algorithm is becoming more and more attractive to the industry because of its robustness in imaging complex geology, e.g. sub-salt (Boechat et al., 2007; Jones et al., 2007).

McMechan (1983,1982), Whitmore (1983) and Baysal et al. (1983) first used reverse-time migration for poststack or zero-offset data. The procedure underlying poststack reverse-time migration is the following: first, reverse the recorded data in time; second, use these reversed data as sources along the recording surface to propagate the wavefields in the subsurface; third, extract the image at zero time, e.g. apply an imaging condition. The principle of poststack reverse-time migration is that the subsurface reflectors work as exploding reflectors and that the wave equation used to propagate data can be applied either forward or backward in time by simply reversing the time axis (Levin, 1984).

Chang and McMechan (1986) apply reverse-time migration to prestack data. Prestack reverse-time migration reconstructs source and receiver wavefields. The source wavefield is reconstructed forward in time, and the receiver wavefield is reconstructed backward in time. Chang and McMechan (1994,1986) use a so called excitation-time imaging condition, where images are formed by extracting the receiver wavefield at the time taken by a wave to travel from the source to the image point. This imaging condition is a special case of the cross-correlation imaging condition of Claerbout (1971).


next up previous [pdf]

Next: Elastic imaging vs. acoustic Up: Wavefield imaging Previous: Wavefield imaging

2013-08-29