Extended range optical velocimetry through spatial correlation of image speckle sub-patterns

A method for measuring, in an extended range, the linear velocity of a movi ng rough surface is proposed. To this end, two image speckle patterns origi nated by the coherently illuminated surface are detected and processed as a set of speckle sub-patterns, each one obtained from a partition of both de tected intensity distributions along the motion direction. A quasi-real-tim e fast spatial correlation operation between the speckle sub-patterns is ca rried out in order to find the maximum correlation value. Its localisation determines the velocity of the surface, while the shape of the correlation peak allows to evaluate the uncertainty of the measuring procedure. An expe rimental verification is performed to illustrate the feasibility of this ap proach. (C) 1999 Elsevier Science B.V. All rights reserved.