Abstract
A novel method for the measurement of velocity in a plane using crosscorrelation functions is presented. Signals are obtained from a random surface of an object by a circular array sensor of 64 photodiodes. Crosscorrelation functions R(m, n) (n=1, 2, …, 32) are computed from 32 pairs of photodiodes; each pair consists of 2 photodiodes placed at the both ends of a diameter of the sensor. Magnitude and direction of a velocity of the object is determined from m=m0 and n=n0 where a maximum of R(m, n) is found.
It took less than 1/25 s to compute the correlation functions R(m, n) by a correlator made for our experiments. The present method was found to be of much practical use by experiments: (1) A rotating disk with random surface was observed by the circular array sensor; the point observed by the sensor, as seen from the disk, traveled along a circle on the disk surface. A travel distance of the point was measured to an accuracy of 0.1%. A center and angular velocity of its circular motion were also determined accurately. (2) Flow velocity distribution of a water surface was measured by displacing the sensor and, for example, a position of a vortex center was measured to an accuracy of 0.4mm.
