Garis besar topik

  • A equipment that uses ultrasonic waves to locate fish in the sea is called a fish finder. If we can use a fish finder to determine the location of a school of fish while towing the net at that location, we can collect samples efficiently. In addition, in order to tow the trawl net over the seafloor surface more reliably and safely, the depth of the research area and the undulations of the seafloor must be captured in detail with an echo-sounder.

    Figure 12 Acoustic measurement equipment used for fisheries surveys

    a) Scanning sonar: Transmits ultrasonic waves around the entire area and captures the reflected waves from the sea to detect schools of fish in an area. The detection range can be adjusted by changing the angle of the sonic beam (depression angle). b) Quantitative echo sounder: A quantitative echo sounder measures and records the strength and number of sound waves (echoes) returned from a school of fish to enable quantitative evaluation of the characteristics of the fish school. The measurement results from a quantitive echo sounder are output as an image "echogram," which is a color-coded display of the depth from which the echoes returned and the intensity of the reflections. c) Multi-narrow-beam bathymetry: Measures water depth over a wide area by transmitting multiple highly directional sonic beams in a fan shape. It is also called a seafloor topography survey equipment because it can depict the undulations of the seafloor in three dimensions.