Systematic Errors and Corrections of CurrentVelocity Measured by Shipmounted Three-Beam Type ADCP

Abstract

At present, one of the most widely used instruments to measure current velocity in the ocean is shipmounted ADCP (Acoustic Doppler Current Profiler). The ADCP measures current speed by sending out acoustic pulses downward from transmitters mounted on the ship bottom, and then by processing the Doppler shift of the acoustic signals scattered by particles in the water. Three-beam type ADCP using 3-element transducers has been widely used in Japan including the vessels of Japan Coast Guard, as well as four-beam type. Although shipmounted ADCPs are very useful for current measurement, non-realistic current data are sometimes obtained mainly due to errors of ship velocity relative to sea water. In this technical article, systematic errors in current measurement by shipmounted three-beam type ADCP and error correction are described in detail.