A Normal Mode Solution for Low-Frequency Bottom-Refracted Wave Propagation

A normal mode solution for low-frequency bottom-sediment-refracted wave propagation is formulated for use with a normal mode method of solving the Helmholtz wave equation to describe the underwater sound field for a fixed point source in a plane multilayered medium. The approach utilizes a factorization of the Wronskian of Green´s function which enables sediment reflecting and refracting modes to be summed independently. The sensitivity of propagation loss to the nature of mode interaction with the bottom is investigated for multiple frequencies in a sample environment, and results are compared to measurements of 100-Hz bottom returns in the Caribbean Basin.