Localization and geoacoustic inversion by using 20-Hz signals of finback whales on the New Jersey Shelf

Abstract

One-second duration 20-Hz signals of finback whales were recorded on three vertical line arrays (VLAs) and a bottomed horizontal line array (HLA) during the RAGS03 experiment conducted on the New Jersey Shelf. Modal analysis indicated that most signals, recorded over a 3-week period in December of 2003, contained a weak, early-arriving mode-2 and strong, late-arriving mode-1 component. These modal characteristics are exploited in a broadband matched-field algorithm to localize individual finback whales and to perform geoacoustic inversions. Bearing estimation of individual whales is obtained by performing horizontal beamforming on the HLA data. Range estimation results are verified by time-of-flight triangulation using single hydrophone data from each VLA location. Geoacoustic inversion results were comparable to those previously obtained from chirp sonar data. Localization results indicated that most finback whales traveled near the shelfbreak front where food might be abundant. [This work was supported by the ONR.]