Deduction of bottom reflection phase change using normal modes

Abstract

For discrete normal modes in shallow water, the mode characteristic equation is known to depend on the phase change of bottom reflection. Precise measurement of mode time‐frequency dispersion has enabled us to deduce the phase change using just the shot data. We discuss the method and present the phase‐change data for grazing angles between 9° to 10.4°. This proves to be a useful technique since direct experimental measurement of phase change is extremely difficult. Past work which investigated the bottom properties have concentrated on the reflectivity coefficients. We find that the phase‐change information can also shed light on the acoustic properties of the bottom. It is hoped that this technique for measuring the phase change will be utilized to gain further understanding of the ocean bottoms.