A phase based detector of whale clicks

In this paper we present an alternative way to usual energy based approaches for detecting whale clicks. We suggest the use of the phase spectrum since the information about the location of clicks is very well represented in phase spectra. The method is referred to as the phase slope function. It is shown that the phase slope function is robust to additive noise while it offers simplicity in click detection since it is independent of the click source level. We further discuss its properties regarding the mono-pulse and multi-pulse character of clicks by introducing the notion of center of gravity for clicks. To evaluate the suggested phase based whale click detector we labeled clicks by hand in recordings of sperm and beaked whales provided by the Atlantic Undersea Test and Evaluation Center (AUTEC). Conducting detection tests demonstrate that 88% (on average) of the hand labeled mono-pulsed clicks were detected within an accuracy of less than 1 ms. Regarding the detection of multi-pulsed clicks we were able to detect over 95% of them by considering a multi-pulsed click as one acoustic event and not as a series of pulses.