Finite-differencing in the time domain

IEI develops time-domain finite differencing methods. Since the earth velocity is unvarying in time, a ``basics only'' book such as this omits this topic since you can, in principle, accomplish the same goals in the $\omega$-domain. There are some applications, however, that give rise to time-variable coefficients in their partial differential equations. Recursive dip filtering is one application. Residual migration is another. Some formulations of DMO are another.