Analysis of marine mammal bearing tracks from two-hydrophone recordings made with a glider

Abstract

An underwater glider fitted with two hydrophones recorded approximately 19 hours of data during an opportunistic sea experiment in the summer of 2014. The acoustic data were collected with a sampling frequency of 96 kHz and 16-bit resolution in deep waters off the western coast of the island of Sardinia, Mediterranean Sea. Detection and classification of sounds by a trained human analyst indicated the presence of sperm whale (Physeter macrocephalus) regular clicks as well as dolphin clicks and whistles. A period of 90 min during which the glider did not surface, and which contained extensive sperm whale clicking activity was chosen for analysis. Cross-correlation of the data from both channels allowed the estimation of the direction (bearing) of clicks, and realization of animal tracks. Several bearing tracks were observed through this analysis, closely following the oscillatory pattern of the glider’s heading, suggesting that such information has the potential to break the left-right ambiguity of the bearing estimates. Results from the bearing tracking analysis, including accuracy and performance, will be shown followed by a discussion on how they can aid in population density estimation studies.