Bottom-mounted hydrophones used to investigate sperm whale click and swim characteristics

Abstract

A method that relies solely on the time difference between direct and reflected arrivals (DRTD) on individual hydrophones was previously used to localize a single sperm whale [E.-M. Nosal and L. N. Frazer, Appl. Acoust., Special Ed.: Detection and Localization of Marine Mammals using Passive Acoustics (in press)]. Regular clicks in recordings from five bottom-mounted hydrophones in the AUTEC range were used in the localization. In this study, the DRTD method is extended by incorporating time differences (between hydrophones) of direct arrivals to refine the track of the whale and to determine the time of generation of individual clicks. Clicks, which have a multi-pulse structure, are analyzed in detail to determine changes in interpulse intervals (IPI) with time. The resulting time, location, and IPI information are used to investigate swim patterns and directionality characteristics of regular sperm whale clicks. [Work supported by ONR. Data provided by NUWC for the 2nd International Workshop on Detection and Localization of Marine Mammals using Passive Acoustics.]