Translations:Migration - book/11/en

Let us now outline how 3D imaging is done. The 3D volume (x,y,z) represents the earth, where (x,y) represents the surface coordinates and z represents the depth coordinate. On the surface plane (x,y), the sources and receivers are arranged in a 2D grid. The (two-way) traveltime t is the duration of the passage of a primary reflection down from the source $\left(x_{s},y_{s}\right)$ to a depth point (x,y,z) and then up to the receiver $\left(x_{r},y_{r}\right)$. A digital trace is a discrete sequence of amplitudes as a function of discrete traveltime. Thus, the amplitude $f\left(x_{s},y_{s},x_{r},y_{r},t\right)$ represents the sum of all primary reflections with traveltime t originating from source $x_{s},y_{s}$ and recorded at receiver $x_{r},y_{r}$.