Analysis of cetacea vocalizations using ocean bottom seismic array observations, western Woodlark Basin, Papua New Guinea.

Abstract

Over a 6-month period in 1999 an array of seven ocean bottom seismometers and seven bottom mounted hydrophones covered a 30-km2 area at 2–3-km water depth in the western Woodlark Basin. The array’s main task was the detection of microearthquakes associated with nearby active tectonics. However, it also made fortuitous broadband recordings of Cetacea vocalizations that we associate with finback whales. Each of these signals has a 10–15-s duration and they exhibit a repetitive pattern with 10–15-min period. The signals are well recorded across both the seismometers and hydrophones, which were sampled at 64 and 125 Hz, respectively. Time-varying spectral analysis demonstrates that the signals are frequency modulated in the 20–30-Hz band with most energy occurring at ∼22 Hz. We employ array-based methods (e.g., optimal beam forming techniques) and acoustic transmission loss simulations to determine range and bearing of the acoustic sources. Preliminary analysis indicates that the acoustic sources originate near the array, and secondary signals may represent back-scattered energy from the short-wavelength, high-topographic features associated the active tectonics with in the basin.