How and at what stage of the processing are non linear movements taken into account?
Non-linear movements are taken into account only during the final phase of ground motion estimation. The first steps of PS Technique are aimed to Atmospheric Phase Screen (APS) evaluation and removal. A subset of points called Permanent Scatterers Candidates (PSC) have to be selected for this purpose, chosen among the ones affected by linear deformation. This does not represent a limitation, as the target here is not to extract all the information available, but only a sparse grid of points where the APS can be evaluated. Exploiting the low-pass spatial behavior of the atmospheric disturbance, the signal is then reconstructed over the whole image and removed, allowing one to perform the final deformation analysis. At this stage it is possible to use linear as well as higher order model for motion.
