David K. Mellinger
Bioacoust. Res. Prog., Cornell Univ., 159 Sapsucker Woods Rd., Ithaca, NY 14850-1999
Beth A. Weisburn
Stephen G. Mitchell
Christopher W. Clark
Cornell University, Ithaca, NY 14850-1999
Finback whales (Balaenoptera physalus) emit pulses of approximately 20 Hz at 10 to 20-s intervals. A method is presented here for measuring the pulse rate of whales; the method may potentially be useful for tracking individual whales over time, for characterizing sounds of finback herds, or for behavioral study. The method uses the finite-time-support summed autocorrelation, which is computed by taking a finite time window of a signal, autocorrelating and squaring, and then summing the autocorrelation over multiples of possible finback pulse periods. Repeating this operation over time gives a map of extant pulse periods over time, in which peaks are then tracked. The method is tested on several hour-long and longer recordings of finback calls obtained from U.S. Navy SOSUS arrays. Call SNR's vary from 30 dB to below 0 dB. The method is found to be effective even at very low SNR. In addition, it is capable of measuring and distinguishing pulse periods of several simultaneously calling finbacks, a critical property for studying this type of whale. The method also is compared to other techniques for measuring periodicity, including Fourier analysis and autocorrelation, and found to work better on the test signals studied. [Work supported by ONR.]