Fisheries scientists have for many years been requesting a calibrated multibeam echo sounder/sonar specially designed for fishery research applications. Simrad AS has, in cooperation with IFREMER, France, agreed on specifications for a multibeam echo sounder and with IMR, Norway for a multibeam sonar, and contracts were signed for development of such systems in January 2003. The systems have 800 transmitting and receiving channels with similar hardware, but different software, and are characterized by narrow beams, low-sidelobe levels, and operate in the frequency range 70–120 kHz. The echo sounder is designed for high operating flexibility, with 1 to 47 beams of approximately 2°, covering a maximum sector of 60°. In addition, normal split beam mode on 70 and 120 kHz with 7° beams for comparison with standard system is available. The sonar will be mounted on a drop keel, looking horizontally, covering a horizontal sector of ±30°, and a vertical sector of 45°. Total number of beams is 500, 25 beams horizontally with a resolution of ∼3°, and 20 beams vertically with a resolution of ∼4°. Both systems are designed for accurate fish-stock assessment and fish-behavior studies.

is thanked for sharing his extensive knowledge. Also other members of the Marine Ecosystem Acoustic group at IMR are thanked for their advice, discussions and for providing an enjoyable working environment. Dezhang Chu is thanked for hosting and supervision during the stay in Seattle.

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