A Laser Doppler Velocimetry (LDV) System for Fish Bypass Evaluation

Laser Doppler velocimetry (LDV) systems have been used for a number of years in field and laboratory applications. The normal LDV system consists of a two-color, four-beam system for obtaining two-component velocity measurements. These systems perform well in open flow but are not capable of obtaining velocity measurements along surfaces unless an angle is added to the LDV system probe. But adding an angle to the probe alignment introduces a small error into the measured velocities. The error can be as high as 1.38 percent of the vertical component for a system with a 50-mm beam spacing and a 600-mm focal length.