Echolocation signals of wild white beaked dolphins measured with a four-hydrophone short base line array in real-time

Abstract

The echolocation signals of Lagenorhynchus albirostris were measured in the waters off Keflavik, Icelend during 22–26 August 1998. A four-hydrophone array was used with each hydrophone located at the tip of an equilateral triangle and one located at the center of the triangle. Each of the outer three hydrophones was spaced 0.61 m from the center hydrophone and the separation angle between outer hydrophones was 120 deg. An underwater video camera was attached 10 cm from the center hydrophone. The array was mounted on a long pole that was lowered to a depth of about 2 m from the side of a 10-m diesel driven boat. The hydrophones were connected to two GAGA-1210 data acquisition boards operating at a 500-kHz sample rate. The computer clock was synchronized with the clock on portable video recorder. Two-hundred pretrigger and 200 posttrigger points per channel with four channels of data were acquired simultaneously and stored in the memory of a transportable computer. The results indicate that the white beaked dolphins emitted high-frequency clicks with peak frequencies close to 120 kHz. The maximum source level of the echolocation signals was 219 dB and the source levels increased with range from the array.