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    • This page provides an easy-to-read overview of the class and relevant links.
      For the most up-to-date "Class Plan", "Grading Criteria and Methods," and other information,
      be sure to check the official syllabus of Hokkaido University.

  • 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.

    海洋音響学１

    海洋音響学２

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

    魚群探知機（上左図）
    魚群探知機で見た鉛直下の海中の様子（＝エコーグラム）。上：低い周波数。下：高い周波数。横軸方向が時間、縦軸方向が深さを表す。魚や魚群の垂直分布（2次元）の把握や現存量推定に使われる。
    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.

    ソナー（上中図）
    ソナーで見た船の周りの海中の様子。円の中心が船。周りに見える赤い塊が魚群。船を中心として音響ビームであちこち振ることができるため、3次元の魚群分布や船から離れたところの魚群を探知することができる。
    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.

    音響カメラ（上右図）
    音響カメラで見たイカの体内。無灯火状態でも光学カメラでみたように観察できる。海中での形状や行動、体内構造などを調べることができる。
    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)