This chapter attends to those details that enable us to do a
high-quality job of downward continuing wavefields.
There will be few new seismic imaging concepts here.
There will, however, be interesting examples of pitfalls.
And in order to improve the quality of seismic images of the earth,
several new and interesting mathematical concepts will be introduced.
Toward the end of the chapter
a program is prepared
to simulate and compare various migration methods.