Abstract:

An experimental method is described for mapping the wave-number spectrum of the normal-mode field as a function of position in a complex, shallow-water waveguide environment whose acoustic properties vary in three spatial dimensions. The experimental configuration consists of a fixed source radiating one or more pure tones to a field of freely drifting buoys, each containing a hydrophone, GPS and acoustic navigation, and radio telemetry. The precisely navigated, drifting hydrophones form a two-dimensional, synthetic aperture planar array that can be used to determine the evolution of the normal modes in range and azimuth. By describing the spatially varying spectral content of the modal field, the method provides a direct measure of the propagation characteristics of the waveguide. The resulting modal maps can also be used as input data to inversion techniques for obtaining the acoustic properties of the waveguide. [Work supported by ONR and ARL Penn State Univ.]