Collaborative Research: Calibrating Multibeam Sonars for Surveying Midwater Fish

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This collaborative project between the Woods Hole Oceanographic Institution and the University of New Hampshire addresses an ocean science and fisheries management requirement for improved capabilities for measuring the abundance and distribution of fish and other organisms in the open ocean. Newly available multibeam echo sounders provide the capability to record and analyze acoustic returns on individual beams, which represents a new capability for the ocean research community. A multibeam echo sounder will be tested and calibrated in three venues: fresh-water test tank, sea-well test facility, and in situ on a towed vehicle. The objectives of this calibration exercise are the determination of the on-axis response, sensitivity limits, hence dynamic range, and directivity patterns for each beam. The use of acoustic measurements for fish stock abundance and other research applications has been established, but the potential for measuring the numerical density of fish is difficult without a means of calibrating the system in situ. Results from this sonar calibration project will provide a means for attaining better areal coverage without compromising spatial resolution.