Using broadband humpback whale vocalizations to locate nonvocal whales in shallow water

Abstract

In a previous paper [Makris and Cato, J. Acoust. Soc. Am. 96, 3270 (1994)], it was shown that a vocal member of a humpback whale herd can be used as a source of opportunity to locate nonvocal members with a passive towed array. That analysis employed full-field but narrow-band propagation and scattering models to emphasize the high spatial array gains available. In the present paper, full-field simulations are performed to determine the structure of actual broadband humpback whale vocalizations after scattering from whales in a shallow-water waveguide. The simulations show that the time signature of a whale vocalization is significantly altered during each of the three stages of (1) propagating from vocal to nonvocal whale, (2) scattering from the nonvocal whale, and (3) propagating from the nonvocal whale to a receiver. The large time-bandwidth gains available in humpback vocalizations then cannot be optimally exploited without first modeling broadband propagation and scattering of the whale vocalization for the given waveguide and bistatic geometry. This raises serious questions about whether the humpbacks themselves, who have limited spatial gains over the noise, can actively detect nonvocal herd members with their vocalizations, as was discussed in the above reference.