Comparative results of optical analog and digital calculation of a number of two-dimensional auto- and cross-correlation functions are presented. The technique of optical correlation is shown to be reasonably accurate and is, therefore, of potential value as a signal processing tool.

Conventional microwave radar is used extensively by meteorologists in locating and tracking percipitating storms, and to some extent, by cloud physicists in determining physical characteristics of dense cloud. The more recent availability of highly collimated, nearly monochromatic, short-pulse light beau s from laser sources makes it possible to use the radar technique for remote detection and easurement of minute concentrations of very small particles, down to those having dimensions on the order of the wavelength of light.

Photographic line images of atomic spectra are used by atomic physicists to determine electron energy levels of atoms. The precision and accuracy of these energy measurements depend to a great extent on the quality of the photo graphic images produced by a spectrograph.

Present automatic stereocompilation instruments use electronic correlation techniques to match conjugate image areas in stereo photographs. Recent studies have demonstrated the possibility of performing the same task by means of coherent optical processing. This paper compares the merits and constraints of the two approaches. Each correlator system is described with particular emphasis on how control signals for precise automatic image registration and deformation correction can be generated and applied in the optical correlation system. It is concluded that automatic optical image correlation offers advantages over its electronic counterpart in simplification of the correlation computer and the ability to handle high photographic density. However, further work is needed to achieve optically the flexibility available with the electronic correlator.