Techniques for separating interfering blue and fin whale calls

Abstract

Recordings of blue and fin whales were made at the Southern California Offshore Range (SCORE) in August 2003. In analyzing this data, previously successful tracking algorithms, based on time differences of arrival (TDOA) measured on geographically distributed hydrophones, were frustrated by the mutual interference between the shorter, broadband, but higher amplitude fin whale calls and the longer duration, narrow-band, blue whale calls. We present a series of progressively more powerful detectors designed to isolate these two types of calls, by zeroing in on specific features of these calls. Because the limited bandwidth of both types of calls presents a challenge to time delay estimation, we also present a comparison of a number of TDOA estimators, including correlation of suitably isolated time-series and spectral features. We apply these techniques to data from different years and geographic sites to assess previous anecdotal evidence of strikingly similar calls within groups of blue whales, despite the presumably wide range of physical characteristics among individuals within each group.