VLF pulse propagation in range‐dependent geoacoustic waveguides

Abstract

The finite difference method is used to study VLF pulse propagation (peak frequency of 10 Hz) in shallow water waveguides (100‐m water depth) with range‐dependent depth and geoacoustic parameters out to ranges of 5 km. The method solves the full two‐way elastic wave equation in space and time using an explicit scheme based on centred finite differences. Compressional and shear velocity and density can be varied arbitrarily in a two‐dimensional grid. The models represent continental margin environments with both upslope and downslope propagation. Propagation can be studied in range‐time space, in snapshots of the wave field at given instants in time and in frequency wavenumber space. In soft bottom environments where the shear wave velocity of the bottom is less than the compressional wave velocity in the water, energy is continually leaking into converted shear waves in the bottom and there are no “perfectly trapped modes.” However, for sources and receivers near the seafloor, Stonely waves are observed w...