Fig. 2. Example of an ensonification event, during which an echolocating Grampus scans each of the three receivers (A,B,C). Note how the ensonification moves from hydrophone C to B to A. Full amplitude of the y-axes corresponds to an apparent source level (ASL) of 222 dB re. 1 µPa (pp). Local maxima on each of the three channels are likely to represent signals on or close to the acoustic axis of the sound beam. X marks a single click displayed in detail in Fig. 3.