Fourier and direct time‐marching methods for transient signals

Abstract

The ocean normally vibrates in harmony with the hum of a narrow‐band sound source. Thus, for modeling such signals, time can be removed from the wave equation reducing it to the simpler Helmholtz equation which in essence governs only the intensity of the hum. Computational ocean acoustics has most often focused on this latter case. Broadband signals such as pings, clicks, chirps, and gurgles require far more work. For researchers accustomed to narrow‐band models the fastest approach is usually to simply add a frequency loop to their narrow‐band codes. (Of course, the run time goes up in accordance with the number of frequencies required.) Others have advocated the development of new models that solve the wave equation directly in the time domain. These options are surveyed and illustrative examples are provided using both idealized test cases and measured data from a recent experiment in the Gulf of Mexico.