An autonomous acoustic recorder using a directional sensor for locating calling bowhead whales

Abstract

A new directional acoustic recorder has been developed to assess the movement and distribution of vocalizing marine mammals. Called DASAR (Directional Autonomous Seafloor Acoustic Recorder), the instrument incorporates an omnidirectional and two orthogonal horizontal sensors from a DIFAR (DIrectional Frequency and Recording) sonobuoy, as well as a magnetic compass. With appropriate processing, the horizontal directions can be computed for received sounds. The acoustic bandwidth is 1000 Hz, appropriate for bowhead calls, and recording is continuous for 45 days. DASARs were deployed in a hexagonal array seaward of an artificial gravel island recently constructed for oil and gas production northwest of Prudhoe Bay, Alaska. Operation was during the fall migration of bowhead whales past the island. The objective was to relate calling-whale locations to the character and levels of sounds emanating from the island and from nearby tugs and barges. [Work supported by BP Exploration (Alaska).]