The NATO Undersea Research Centre (NURC), from its earliest history, has studied a very broad range of underwater acoustic phenomena and their application to surveillance, detection, oceanography and, more recently, port protection. The principal measurement device used to probe acoustic signatures in the ocean is the hydrophone: a transducer that converts pressure fluctuations in the water, caused by the propagation of an acoustic wave, into an electrical signal. In its simplest and most common form, the hydrophone is designed to respond directly to the pressure in the incident sound wave, which, as a scalar quantity, tends to give the hydrophone a receiving directivity characteristic that is omnidirectional (see Box 1). Single hydrophones have been used at NURC since the early 1960s for measurements aimed at investigating acoustic propagation and ocean ambient noise characterization.

Barbagelata, A., P. Guerrini, and L. Troiano. 2008. Thirty years of towed arrays at NURC. Oceanography 21(2):24–33, https://doi.org/10.5670/oceanog.2008.49.

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