Now we can easily find the datuming operator by transposing and taking the complex conjugate of each matrix in the forward-modeling operator shown in equation (). The datuming operator for a poststack data set gathered on an irregular surface is thus
In equation (), we can see that the downward extrapolation ET is preceded by the filter GT at every depth level. We then apply the downward extrapolation operator WiT to the wavefield that was introduced by the operator Fi up to a given depth level. The portion of the wavefield that is not introduced until a given depth level is removed by the operator Ki. Figure shows this datuming operator, while the topography is given by Figure .
Coincidentally, this datuming scheme is the same as Reshef's Reshef (1991). He used the algorithm for depth migration from irregular surfaces with depth extrapolation. We can deduce that Reshef's algorithm assumes the same forward modeling algorithm as this one. By having both the forward operator and its adjoint we are prepared for inversion and velocity estimation.
Figure 4 Synthetic model with a syncline reflector image (lower) under an undulating surface (upper).