ELIMINATION OF EVANESCENT ENERGY

In the ideal solution, evanescent components corresponding to the real eigenvalues would be eliminated, whereas components corresponding to the imaginary eigenvalues would be unaltered. Unfortunately, in the general case this requires the separation of evanescent components through a costly matrix diagonalization. A method for eliminating the evanescent components without the matrix diagonalization and without severely affecting the nonevanescent components is therefore required. A scheme proposed in Kosloff and Kessler (1987) included use of a spatially variant, high-cut filter to P and $\partial P / \partial z$after each step of the propagation of the solution. The high-cut wavenumber k_cut at each point of application was based on the criterion $k_{cut}={\omega /c_{max}}$, where c_max denotes the highest velocity in a taper region surrounding the point of application.