Image-velocity sensors find application in aerial camera-control systems by providing the servo intelligence necessary to achieve accurate image-motion compensation. This paper explores the theory of operation of image-velocity sensors which employ a parallel-slit reticle to effect the light flux modulation resulting in a time frequency directly proportional to image velocity.
Experimental data is presented, and a graphical analysis is used to demonstrate the computing action of the parallel-slit sensor. The effect on signal quality of varying certain geometrical parameters is demonstrated, and limitations of the method are explored. An interesting conclusion is that the computing action is not dependent upon any inherent periodicity in the image. An approach to explaining the phenomenon by information-theory principles is outlined, and practical considerations involved in utilizing this effect in aerial photography are briefly explored.
J. T. ATOR, "Image-Velocity Sensing with Parallel-Slit Reticles," J. Opt. Soc. Am. 53, 1416-1419 (1963)