As we mentioned yesterday, whales and dolphins make a wide variety of sounds which span a range of frequencies from very low (<50hz)>100kHz). Because humans can only hear in a narrow frequency band (20hz – 20Khz), it is often necessary to see the sounds that we can’t hear (and even those that we can). Using special software, the sounds that are received on equipment behind the ship are visualized on the computer in a spectrogram – a colorful display with time on the x axis and frequency on the y axis.
In the picture, the lines represent the clicks of the Cuvier’s beaked whale, Ziphius cavirostris. The features of their clicks include a center frequency around 40 kHz and spacing about 0.4 s apart. The distinguishing trait is that the pair of lines always appears close together, one represents the directly emitted click from the animal and a second one that is simply the reflection of the click from the surface of the sea. Thus, it is possible for the scientist to look at this picture and identify it as a signature of the Ziphius.