Topic outline

  • What you will learn in Ocean Acoustics

    Underwater acoustics is mainly used as a means of information transmission in the sea because of its lower attenuation compared to light and radio waves. In this course, students learn the fundamentals and applications of underwater acoustics in physical oceanographic measurements such as bathymetry, current velocity, and seafloor topography; biological resource measurements such as fish and plankton; and acoustic ecological measurements of dolphins and whales. In particular, students learn about the characteristics of ultrasonic waves, which are neither visible to the human eye nor audible to the human ear, and various measurement methods, as well as the principles of the instruments shown in the figure below and the ecology of organisms revealed by their use.



    音で海中をのぞく:Look under the sea with sound

    Echo sounder(upper left figure)
    A vertical underwater view as seen by a echo sounder (= echogram). Upper: low frequency. Lower: high frequency. The horizontal axis represents time and the vertical axis represents depth. It is used to determine the vertical distribution (two-dimensional) of fish and fish stocks and to estimate their present abundance.

    Sonar (upper middle figure)
    Underwater view around the ship as seen by sonar. The center of the circle is the ship. The red mass around the ship is a fish community. Since the acoustic beam can swing from place to place with the ship at the center, it is possible to detect the three-dimensional distribution of fish community and fish community far from the ship.

    Acoustic camera (upper right higure); The inside of a squid's body as seen by an optical camera, even without lights on. It is possible to examine the shape, behavior, and internal structure in the sea.

    生物の日周移動(計量魚群探知機):Diurnal migration of organisms (quantitative echo sounder
    魚群の形状(ソナー):Shape of the fish population(Sonar)
    海底上の構造物(上:音響画像、下:カメラ画像)(サイドスキャンソナー):Structures on the seabed (Upper: acoustic image, Lower: camera image) (side-scan sonar)
    イカの音響映像(音響カメラ):Squid acoustic video (acoustic camera)