Normal-mode solution in the ocean with absorbing bottom sediments which have a sound-speed gradient.

The sound field in a horizontally stratified ocean with absorbing bottom sediments is written as a normal-mode sum. The branch-line integrals are not necessary to take into account when the squared index of refraction is approximated with a linear gradient form in both water and sediment layers. It is assumed that the boundaries are parallel and that the sound-speed varies only with depth. Under the circumstances, we may find single-valued and analytic complex functional properties of the determinant in the characteristic equation. Noticing the points, this paper presents a normal-mode theory and numerical techniques in determining eigenvalues. As an illustrative example, calculations are made for a medium depth ocean and compared to field data.