Acoustical localization of dolphins in shallow water

Abstract

Previous attempts at localization of cetaceans have generally used multiple hydrophone arrays and multichannel recording systems. In this paper a low-budget localization technique using only one hydrophone will be described. The time delays of the signals traveling on the surface and bottom reflection paths to the hydrophone, relative to the direct signal, are used to calculate the distance and the depth of a phonating animal. Only two additional measures, the depth of the bottom and hydrophone, have to be taken. The method requires relatively shallow waters and a flat ground surface. The received signals are digitized directly into a laptop computer via a PCMCIA A/D converter card with a sampling rate of 260 ksamples/s. Hawaiian spinner dolphins (Stenella langirostris) were localized by echolocation and burst pulse click trains over different bottom substrates. The method is most valuable for examining source levels of dolphin clicks in the wild and could lead to a better understanding of the nature and use of click trains by dolphins. [Work supported by Deutsche Forschungsgemeinschaft and Office of Naval Research.]