A testing procedure is presented to estimate topography and deformation parameters from an interferometric stack (a number of reference phase corrected interferograms w.r.t. the same master image). A subset of pixels exhibit coherent phase in time, and a time series of phase differences between pairs of these pixels allows to set up a system of equations. A null hypothesis of zero deformation can be tested against alternative hypotheses, specifying linear and non-linear deformation. The covariance matrix of the phase differences accounts for phase noise, atmospheric effects, and orbit inaccuracies.