Abstract:

Theory shows that the wave-number spectrum of a propagating normal-mode field is a function of position for a complex, shallow-water waveguide whose acoustic properties vary in three spatial dimensions. To demonstrate these effects, a modal mapping experiment (MOMAX) was conducted in the vicinity of the East Coast STRATAFORM site. Using both fixed and drifting source configurations, several pure tones in the range 50--300 Hz were transmitted to a field of freely drifting buoys, each containing a hydrophone, GPS and acoustic navigation, and radio telemetry. The resulting two-dimensional, synthetic aperture planar array can then be used to determine the evolution of the normal modes with position. By measuring the spatially varying spectral content of the modal field, propagation characteristics of the waveguide may then be inferred. Preliminary results will be presented for different source and buoy configurations demonstrating modal evolution as a function of position. Supporting environmental and model data will also be presented and correlated with the experimental results. [Work supported by ONR.]