UUV COVERT ACOUSTIC COMMUNICATIONS

The research project UUV Covert Acoustic Communications aims at furtive communication between unmanned underwater vehicles and a distant mother platform. Suitable modems were developed, which were tested in Norwegian coastal waters during a demonstration trial in September 2008. One modem was lowered into the water column from a mother ship, whereas the other modem was integrated in an autonomous underwater vehicle. In order to address the aspect of covertness, intercept sonobuoys were dropped in the area and their data processed by an automated energy detector and a sonar operator. The results show that it is difficult to communicate covertly under all circumstances, especially if the interceptor is close to the transmitter or experiences more favourable propagation conditions than the communicator. Conversely, covert operation is possible when the communicator experiences better conditions than the interceptor. In case of equal conditions, the communication can also be covert with the interceptor requiring some 6 dB higher SNR for detection than the communicator for decoding. Moreover, the communication link proves very robust with respect to interference whereas the energy detector suffers from multiple false alarms in the presence of transients unrelated to the communication system.