Measurements of the frequency dependence of normal modes

Abstract

An experiment using a vertical array to detect acoustic normal modes in shallow water is described. A high signal-to-noise ratio was achieved by the use of pseudorandom pulse sequences to modulate the projector. Wide bandwidth signals and a tunable acoustic source enabled the frequency dependence of normal modes to be measured and results are in good agreement with the theory. An improved method of extracting the signal present in a single mode is described and used to examine pulse shapes and frequency spectra of individual modes.