A remotely-piloted acoustic array for studying sperm whale vocal behaviour

The vocal behavior of sperm whales was investigated using a remotely-piloted acoustic array. Acoustic array consisting of remotely-piloted vessels (RPVs) and hydrophones was deployed from a stationary 12-m sailboat and positioned as to form a favorable array geometry around a group of sperm whales. Two metal pipes were suspended from a wood plank with a distance of 1.5 m between them and hung over the sides of dinghy. The dinghy was rowed through the array and a hammer was used to strike the pipes to generate impulsive sound sources of different frequencies. Using time-of-arrival-differences (TOADs) between hydrophones, the position of GPS receivers, and the speed of sound in water, the location of a detected sound was calculated. It was observed that the hydrophone of RPV offered accurate estimate of the sound source's location. Result shows that the acoustic array offer an accuracy of 0.5 m within the array for differentiating the coda vocalizations exchanged between sperm whales.