Figure 2 Input source wave field at time equals zero and velocity function used for the model.
The result of the forward time-extrapolation is shown in Figure , on the top of the snap shots. It contains the direct arrival, primary reflection, ghost and multiple reflection events. In order to avoid the inclusion of the boundary reflections, time extrapolation was performed before the arrival time of the boundary reflections (see the snap shots in Figure ). Figure shows the result of the reverse-time migration using the algorithm presented in this paper. It can be seen that the conjugate operator does a good job. The backprojected source wave field recovered closely matching the original source function except for some artifacts. These artifacts are mainly caused by the wave fields propagated downward, and can be suppressed using a least-squares optimization technique (Ji, 1992) by solving an objective function as follows:
Figure 5 Comparison of wave fields: Top is the original wave field. Middle is the result of conjugate operator. Bottom is the result of the least-squares inversion (after 10 iteration).