Explicit 15 degree migration equation

We saw that the retarded 15$^\circ$ wave-extrapolation equation is like the heat-flow equation with the exception that the heat conductivity $\sigma$ must be replaced by the purely imaginary number i. The amplification factor (the magnitude of the factor in parentheses in equation (71)) is now the square root of the sum squared of real and imaginary parts. Since the real part is already one, the amplification factor exceeds unity for all nonzero values of k². The resulting instability is manifested by the growth of dipping plane waves. The more dip, the faster the growth. Furthermore, discretizing the x-axis does not solve the problem.