David K. Mellinger
Christopher W. Clark
Bioacoust. Res. Prog., Cornell Univ., 159 Sapsucker Woods Rd., Ithaca, NY 14850
The automatic detection of animal cells has several potential applications: for range, distribution, and, census efforts; for acoustic behavior studies, both local and wide area; for screening of large volumes of data for sounds of interest. Methods were developed for detecting the vocalizations of three species of mysticete: blue, finback, and minke whales. Each call is modeled as a sequence of either bandlimited pulses or frequency sweeps. Sweeps and pulses are detected by cross-correlating a specially designed kernel with a spectrogram of the target sound signal; the kernel is built from the call model, and includes excitatory regions corresponding to the sweeps or pulses in the call, and flanking inhibitory regions to inhibit response to noise and interfering sounds. This method produces as output a time series with values corresponding to the likelihood that the modeled call is present. A time-windowed autocorrelation is then performed on this output, and the result of that is percentile-normalized and thresholded. The final output is a yes/no decision about the presence or absence of a periodic sequence of the desired calls. This process is currently being used for scanning large amounts of sound data from Navy SOSUS arrays; results of this scanning are presented.