Section outline

    • Instruments that measure the movement of an object (speed and direction) using the Doppler effect, which is explained by the phenomenon that the sound of a siren is different when an emergency vehicle is approaching and when it is moving away, are generally called Doppler sonar, and those that measure seawater flow in particular are called Acoustic Doppler Current Profiler(ADCP). Vertical profiles of the flow field in the ocean can be continuously measured by sailing observation using a ship-bottom-mounted ADCP (Figure 2).

    • ADCP

      Figure 2 Tidal current vector diagram obtained by ADCP's sailing observation


    • The basic principle of Doppler sonar is to determine the speed of movement of an object by measuring the amount of change in frequency (Doppler shift) that occurs when sound waves of a certain frequency are transmitted and scattered by a moving object (Figure 3). ADCP transmits sound waves in three or more different directions and measures the movement of multiple layers of seawater in three dimensions by capturing the difference in Doppler shift that occurs when the waves are scattered by particles such as plankton that are moving with the seawater.

    • ADCP 計測原理

      Figure 3 Outline drawing of Doppler shift

      When the scatterer is moving away → frequency drops

      When the scatterer is approaching → frequency goes up