Abstract
The ability to selectively excite single acoustic modes in a shallow-water environment is demonstrated and analyzed. Using vertical source and receiving arrays and the feedback control techniques based on those in Buck et al. [IEEE J. Oceanic Eng. 22, 281–291 (1997)], acoustic modes 1–3 were excited sequentially for periods up to 20 min with a fidelity of approximately 60 dB for mode 1 to 25 dB for mode 3. The filtering of the received signal used in the feedback loop by projection into the subspace spanned by the dominant system modes was found to significantly improve the system’s performance. This result will be explained and analyzed. The requirement for phase stabilization of the sampled received signal is also presented. The ability demonstrated here for high fidelity selectively controlled modal content of a transmitted acoustic signal offers potential for new methods for acoustic tomography and for studying underwater acoustic propagation. [Work supported by ONR Ocean Acoustics.]