Experimental Investigation of Acousto-Optic Communications

Covert communications between underwater and aerial platforms would increase the flexibility of surface and air vehicles engaged in undersea warfare by providing a new netcentric warfare communication capability and could have a variety of commercial and oceanographic applications. Research into an acousto-optic sensor shows promise as a means for detecting acoustic data projected towards the water surface from a submerged platform. The laser-based sensor probes the water surface to detect interface vibrations caused by an impinging acoustic pressure field. A number of experimental and simulation studies were conducted to demonstrate acousto-optic sensor feasibility for obtaining robust recordings of acoustic communication signals across the air-water interface. The recorded surface velocity signals were transferred to an acoustic communication receiver that employs conventional acoustic telemetry algorithms such as adaptive equalization and Viterbi convolutional decoding to decode the signal. The detected, equalized, and decoded bit error rate performance is presented for hydrostatic, more realistic hydrodynamic water surface conditions, and hydrodynamic surface conditions while employing a surface normal tracking unit that is designed to mitigate degradation in communication performance as a result of optical signal dropout.