The measurement of depth motion by speckle photography

We propose three methods for measuring the depth motion (i.e., motion in line-of-sight, not lateral) of bodies with a rough surface by multi-exposure speckle photography. The speckle photographs are processed optically (autocorrelation). The output is a depth-versus-time graph. Two of the three proposed methods have been verified experimentally. The accuracy of the methods can be choosen to be about one wavelength or up to several millimeters.