This paper describes a method of eliminating the bi-directional ambiguity in measurements of theflow velocity using a lenticular grating. The deflection characteristics of the light passing through the lenticularis studied theoretically and it is shown that the lenticular grating works as a phase grating. In avelocimeter using the lenticular grating and the four photodetecters, the opposite directions of the flow arediscriminated from the phase relation between the two signals combined appropriately from the output signalsof four photodetectors.
The method is used to measure the velocity of a random pattern on the rotating disk. The experimentalresults show the usefulness of this method for eliminating the directional ambiguity.