LPI Techniques in the Underwater Acoustic Channel

The characteristics of the underwater acoustic channel present special problems in the design of covert communication systems. In this paper we consider communications at relatively short distances, less than 20,000 yds., and well below the water surface. Covertness is measured in terms of the parameter d associated with the interceptor receiver operating characteristic and curves are given that relate d to the distance ratio between intercepter and receiver. The results clearly show the dominance of the channel characteristic over spreading techniques. Systems can be easily made very covert if the interceptor is further from the source than the receiver but are almost impossible if the interceptor is inside the receiver.