Velocity measurements using a laser Doppler velocimeter on board SS Tydeman

A short survey is presented of a study into the possibility of velocity measurements (of ocean currents) with the aid of a laser Doppler tachometer on board a ship. The laser tachometer works with backscattered light, and 600 nW argon ion lasers are used in the system. The optical system was carried out in such a way that the two velocity components could be measured simply in succession. Three different systems were on board for signal processing namely a frequency follower, a digital transient recorder and a digital photon correlator. All three systems could be coupled coupled via interfaces to a HP 9830 computer for further processing of the measurement data. The HP 9830 system was also used for calculating the position of the measured volume and the transfer constants for each measuring point. The position of the measured volume was adjustable from 0 to 2.5 m calculated from an optical window in the ship's bottom. The dimensions of the measured distance varying about 6 mm near the window to 28 mm at 2.5 m from the window. The transfer constant of window to about 31 kHz per m/s at a distance of 2.5 m from the window.