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An Evaluation of Side-Looking 12 and 100 kHz Sonars for Continuous Surveillance of a Shallow Channel

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Technical Report

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Defence Research and Development Canada Atlantic Dartmouth, Nova Scotia Canada

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This study evaluates data from two high-frequency 12 and 100kHz side-looking sonars which were operated for extended periods in March and October 1997 in Drogden Channel, near Copenhagen, Denmark. This busy shipping channel, 1-km-wide by 12-m-deep, connects the Baltic Sea with the North Sea through the Kattegat. The original purpose of these tests was to demonstrate continuous surveillance for migratory herring, however a variety of shipping traffic was also observed. Quantitative acoustic measurements of ship characteristics and low-grazing-angle seabed reverberation were made with both sonars under a variety of conditions. The sonar measurements were supplemented by simultaneous water temperature, salinity, and current profiles and surface meteorological measurements, allowing some understanding of the environmental influences. The general characteristics were that under normal, homogeneous flow conditions, ships and fish schools were routinely observed up to 400 m range with the 100 kHz sonar and up to 2000 m range with the 12 kHz system. Occasional saline intrusions near the seabed were observed to create strong upward-refracting conditions that significantly altered the available range for target detection, especially for the 100 kHz sonar. Example echo grams and reverberation results for both normal and upward-refracting conditions are shown. Ray-tracing analysis is used to assess the acoustic propagation conditions, specifically to define insonified volumes and shadow zones, and quantify the reflection focusing effects.

Subject Categories:

  • Acoustic Detection and Detectors
  • Biology

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