Adaptation of a three‐dimensional ray tracing code for use with gridded input oceanographic models

Abstract

In order to be able to adapt the Hamiltonian ray tracing program (HARPO) developed by NOAA's Wave Propagation Laboratory for use with gridded numerical oceanographic models, three different approaches have been employed. The first method employs using a 3‐D Fourier decomposition of the sound‐speed field, giving one the ability to use fast Fourier techniques and spatially filter input data but being limited to a constant grid with mesh determined by the highest spatial frequency along a given coordinate. The second technique employs an empirical orthogonal function analysis of the sound‐speed field, the coefficients of which are splined to ensure the continuity requirements of the ray trace. This method allows one to: (1) simply filter the field by mode energy: (2) project easily on oceanographic modes; and (3) vary the sampling to meet the local ocean conditions, thus saving on computer memory requirements. The final technique employed is “feature hanging,” which combines using analytic forms for ocean features and gridded input for their positions. This is an extension of the existing HARPO feature to be consistent with current oceanographic models. Example calculations using each technique will be presented.