The time‐marched FFP for modeling ocean acoustic pulse propagation

Abstract

Traditional ocean acoustic models for cw (time‐harmonic) signals may be extended in an obvious fashion for broadband problems using Fourier synthesis. Alternatively, many of these models may also be solved directly in the time domain that raises the questions of what is the optimal solution and under what conditions. A time‐marched fast‐field program has been developed in which the solution is represented as a sum of Fourier components in range with time and depth‐dependent amplitudes, ɑ(z,t;k). These amplitudes each satisfy a simple hyperbolic equation that is discretized in depth using finite elements and in time by a simple explicit integrator. Snapshots of the ocean acoustic field are then obtained in the usual fashion using an FFT to assemble the various spatial Fourier components. Examples of the method applied to pulse propagation in certain ocean acoustic scenarios will be presented with particular regard to the question of the strengths and weaknesses of the time‐marched FFP versus synthesis from time‐harmonic FFP solutions.