Imaging principle

One of the advantages of the choice of the midpoint-offset coordinate to migrate the data is that the imaging step is both straightforward and inexpensive. There is no need to crosscorrelate and shift wavefields, as for shot-profile reverse-time migration Biondi (2002).

The equivalent of the ``stacked'' image is obtained by selecting the propagated wavefield at zero time and zero offset; that is  

$$I\left(z, x_m\right) = P\left(t=0,z,x_m,x_h=0 \right)$$ (12)

The offset-domain Common Image Gathers (CIG) are obtained by simply selecting the propagated wavefield at zero time; that is  

$$I\left(z, x_m, x_h\right) = P\left(t=0,z,x_m,x_h\right).$$ (13)