George V. Frisk, Laurence N. Connor, and Kyle M. Becker
Dept. of Applied Ocean Physics and Engineering, Woods Hole
Oceanographic Institution, Woods Hole, MA 02543
Barry J. Doust
Applied Research Laboratory and the Graduate Program in Acoustics,
Pennsylvania State University, P.O. Box 30, State College, PA
16804
An experimental method is described for mapping the wavenumber
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.]
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