Source localization in underwater sound fields

We investigated the acoustical information present in the field of arbitrary sound sources which may provide direction and distance to the source from a local reading of the sound field parameters. If the effects of reflections are negligible, the particle acceleration is directed radially at the instant of sound pressure nulls. The spectral relation between the radial component of the particle aceleration and the sound pressure is characterized by a critical frequency where a sharp transition occurs in the amplitude ratio and the phase relation of these variables. The critical frequency depends on the distance to the source and depends little on the source type (mono-, di- or quadrupole). Thus, a local reading of the particle acceleration and the sound pressure is in principle sufficient to localize the sound source in three dimensions. Fish might use this kind of information for acoustic orientation.