CHARACTERIZATION OF SOURCES OF 2-PI PHASE DISCONTINUITY IN SPECKLE INTERFEROGRAMS

One of the most successful phase-unwrapping algorithms uses branch cut s to join discontinuity sources that mark the beginning or the end of a 2 pi phase discontinuity. Here, using phase-stepping speckle interfe rometry, we verify that these sources coincide with points of very low or zero modulus and that the displacement of sources as a result of s peckle decorrelation between measurements of two phase maps leads to c losely spaced dipole pairs of sources in the phase-difference map. By measuring the movement of sources at high magnification, we find that the length distribution of correct branch cuts needed to unwrap a phas e-difference map is approximately Gaussian. This provides a theoretica l justification for unwrapping with the set of branch cuts that minimi zes the sum of squares of cut lengths.