Computing ideal starting fields for parabolic equations: Approach and examples

Abstract

A parabolic equation model requires a starting field, that is, the values of the field must be given as a function of depth at a fixed range. The ideal starting field is a weighted combination of propagating normal modes. Since it is time consuming to compute normal modes, the usual practice is to use a more easily computed result such as a Gaussian, filtered Gaussian, sinc, or uniform ocean starting field. However, in our approach, less effort is required because the individual normal modes are not computed but only the desired combination of normal modes that gives the ideal starting field. Two example normal mode starting fields are computed and are compared to other starting fields. The effects of the various starting fields on the propagation loss predicted by a parabolic equation model are shown.