Signal processing for biological transients emitted by dolphins and snapping shrimp

Abstract

In temperate and tropical waters, the dominant source of biological noise in shallow bays, harbors and inlets is snapping shrimp, which can adversely affect the performance of high-frequency sonar systems. The modified method for passive ranging by wavefront curvature enables the source position and source level of individual snaps to be measured in situ. The results are presented for a sequence of 1000 snaps. The principal habitat of the local snapping shrimp population coincides with a narrow wharf, which is 120 m in length. Next, this passive ranging method is used to localize free-ranging dolphins in their natural habitat. The peak-to-peak sound pressure levels of the biosonar pulses (clicks) emitted by Indo-Pacific dolphins (Tursiops aduncus) are measured for source ranges from 30 m to 300 m, even when the dolphins are echolocating at the same time. The waveforms and signal properties of the click signals are presented, along with their effectiveness for probing the shallow-water environment. The bistatic scattering impulse responses of the sea floor, sea surface and scatterers in the water volume are shown. Finally, consideration is given to the contexts in which snaps and clicks are made.