Research Technical Report

Estimation of the Source Signal Characteristics and Variability of Blue Whale Calls Using a Towed Array

Moore, T.C. (June 1999)

Masters Thesis, Naval Postgraduate School

ABSTRACT

A four-day experiment was conducted to study the feasibility of locating, tracking, and counting blue whales acoustically in the Monterey Bay National Marine Sancutary (MBNMS) at long ranges using the shore-based NPS Ocean Acoustic Observatory (OAO) hydrophone array. In concert with the shore-based acoustic monitoring, an aircraft was assigned to locate whales and a research vessel was manned with observers and instrumented with a towed hydrophone array to determine whale locations and characterize their vocalizations in the near-field. Two transiting blue whales were observed and their vocalizations were recorded by the towed array in close proximity. In this thesis research, these towed array data were deverberated using modeled-based matched signal processing and least-squares fitting. The reconstructed source signals show time durations of 14.4+/-2.2 and 10.6+/-1.6 s and source levels of 162.4+/-7.0 and 166.2+/-10.5 dB re 1 microPa for the 90 Hz "A" calls and 51 Hz "B"calls, respectively. Furthermore, correlation methods were used to quanitfy call-to-call variability. The analysis shows that the waveform of the "B" calls and the magnitude of the waveform of the "A" calls are robust, suggesting that these quantities should be exploited in the design of long-range auto-detection techniques and long-range, model-based localization and tracking algorithms for the OAO array.