Information Embedding in Sonar for Authentication and Identification

In complex undersea environments, where a multitude of simultaneous sonar transmissions may exist, it is desirable to identify a received sonar echo based on its point of origin, platform, and mission etc. This capability can help distinguish friendly sonar sources from counter fraudulent transmissions intended to confuse or mislead. The solution proposed for this problem is to secure embedding of a robust digital watermark in sonar transmissions. The complex short time Fourier transform (STFT) is selected as the domain for embedding the watermark. We show that the watermark can be recovered from a single ping. Moreover, the watermark survives various channel impairments including noise, seabed clutter and multipath. The same concept can be used for covert undersea communications using biologically occurring signals as cover.