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Dolphin Sonar Signals: analysis of bottlenose dolphin clicks

If you hook up your hydrophone to an oscilloscope, the dolphin clicks would appear something like fig.1, the oscillogram, which shows how the signal of a bottlenosed dolphin (Tursiops truncatus) varies over time. It arrives suddenly, and fades away just as quickly, lasting only a few cycles. The timescale is in microseconds (millionths of a second), so the dolphin click lasts less than 50 millionths of a second.

When you analyse such a signal with Fourier analysis, you get the power spectrum (fig. 2), which shows which frequencies present in the signal. The oscillogram and the power spectrum are different ways of showing the characteristics of the signal. The oscilloscope displays the signal's time features and the power spectrum shows its frequency features. Fourier analysis is usually an important first step when invesitgating echolocating animals. The signals are so short in duration though, that modern, specialised methods are inceasingly being used instead.

Fig.1	Fig.2