In this section we briefly discuss several areas that have seen significant development since the book was originally written.

Seismic acquisition: multi-azimuth and wide azimuth

There has been a growing realisation that the reason for poor imaging with standard seismic surveys over regions of rapid velocity change is not just the fact that the image is often highly distorted and needs special migration schemes to image it correctly. In many instances, it is caused by the fact that energy from the target horizons has never made it from the source down to the target and back to the receivers. Often no data have been collected that can be used as the basis for imaging. In such circumstances, no matter how hard we try in the processing, we can never deliver an image of the target reflectors. In addition, strong multiples can interfere with the signal, degrading what illumination we do have.

A good analogy to this situation is an obstacle in the way of your line of sight. If we are trying to look at something and there is an object in the way, the obvious solution is to move to a different position where the view is unimpeded. If the obstacle is small then we might not have to move very far to get a good view, but if the obstacle is large we may need to move some distance before we can see past it. If the obstacle is both large and irregular (say with a few holes or windows through it) then we may not know exactly where we need to stand to get a good view.