Pulse propagation in the ocean. II: The parabolic equation method

Abstract

The Fast Field Program (FFP) is a convenient method to compute the exact integral solution of the wave equation derived from harmonic sources in multilayered media. Solid layers as well as liquid layers may be included in the model. Thus, elastic subbottom layers are included in the model and, for Arctic propagation, an elastic ice sheet is also included. The sound field is computed as a function of range for each detector depth employing the fast Fourier transform (FFT) algorithm. The FFP has been extended to compute waveforms from broadband sources as a function of range and depth by Fourier synthesis employing the FFT algorithm. The input for this synthesis as a function of frequency is computed by the FFP. The computer program has been used to model SOFAR propagation in the central Arctic Ocean. Computed waveforms for the Arctic channel are in excellent agreement with field data. The computations clearly show the evolution in range of the dispersive signals observed in the Arctic channel. At any selected point in range and depth the waveform may be reversed in time and propagated back through the channel, showing the evolution of pulse compression to the range at which the ocean filter is matched and pulse spreading beyond this range.