A range-frequency interference structure is observed in the course of the propagation of ship noise in shallow water of Korea. In shallow water waveguide, modes are formed, each one traveling with its own phase and group velocity. The interference structures are the result of coherently adding the modes. Since different propagation mode groups have characteristic groupphase speed relations, it turns out that this interference structure is also useful for identifying the ocean seabed properties. In this article, a procedure is described for determining the basic geoacoustic parameters of seabed from the measured field of waveguide-trapped acoustic waves. The geoacoustic parameters of the seabed are estimated for the region in which the measurements are performed. Inverse estimation is calculated using full search algorithms based upon genetic algorithm.