Experimental investigation of acoustic channel reciprocity in shallow water

Abstract

Channel reciprocity is recognized as one of the most fundamental properties of underwater acoustic propagation. The theoretical proof of channel reciprocity assumes that the ocean environment is static during the course of acoustic propagation. Since this assumption might not be valid for the case of shallow-water acoustic propagation, a question to be raised is: does channel reciprocity remain true in shallow water? A sea-going experiment was recently conducted to study the shallow-water channel reciprocity. In the experiment, two custom-built software-defined acoustic modems were used to probe their shared channel from two opposite directions. The channel reciprocity was examined by comparing the two probed channels directly. The probing signals and handshaking protocols were judiciously designed to minimize the effects of channel dynamics under the constraint of half-duplex acoustic modems. This paper will provide the details of this sea experiment (including its design, setups and execution) and report interesting findings. [Work supported by US Office of Naval Research.]