We know that the Intrinsic Mode concept, recently introduced for the study of acoustic wave propagation in a penetrable wedge (Arnold and Felsen, J. Soc. Am., 76, 850-860,1984) can be efficiently computed using the FFT algorithm. In many circumstances, such as the prediction of field values along a single row of points parallel to the ocean surface, this method is much more efficient than conventional parabolic-equation and coupled-mode-theory methods, which generate mostly redundant data over entire transverse cross-sections. We present comparisions of acoustic field data generated both by Intrinsic Mode theory, and by the marching algorithms PEM and BPM, which indicate comparable accuracy, though the former method is much more efficient.