Orae-hydrophone method of estimating distance and depth of phonating dolphins in shallow water

Previous attempts at localizing cetaceans have generally used multiple hydr ophone arrays and multichannel recording systems. In this paper, a low-budg et localization technique using only one hydrophone is described. The time delays of the signals traveling via the surface and bottom reflection paths to the hydrophone, relative to the direct signal, are used to calculate th e distance and the depth of a phonating animal. Only two additional measure s, the depth of the bottom and hydrophone, have to be taken. The method req uires relatively shallow waters and a flat bottom surface. Echolocating and burst pulsing Hawaiian spinner dolphins (Stenella longirostris) st the Wai anae coast of Oahu, Hawaii, were localized over different bottom substrates . A tracking range of up to 100 m was achieved. The accuracy of the method is estimated by the total error differential technique. The relative distan ce estimation error is below 35% and the absolute depth error below 0.7 m, so that the location method is sufficiently precise for examining source le vels in our study area. Because of its simplicity, the method ideally compl ements sound recordings and visual sightings of marine mammals and could le ad to a better understanding of the nature and use of click trains by dolph ins. (C) 2000 Acoustical Society of America. [S0001-4966(00)00605-6].