Coregistration of Interferometric Stacks of Sentinel-1 TOPS Data

Abstract

SAR images coregistration is of fundamental importance for the generation of SAR interferograms. The high azimuth coregistration requirements imposed by the TOPS acquisition mode converts the coregistration of stacked time series images in a demanding task due to temporal decorrelation effects. A joint coregistration approach appears to be the optimal solution for coregistering long stacks. The problem of a joint coregistration has been already addressed in the literature for the case of coherently correlating speckle signals. A similar procedure can be applied when employing the established Enhanced Spectral Diversity (ESD) technique for azimuth coregistration of TOPS images. The methodology for the retrieval of the (rigid) azimuth shift of a slave image with respect to a master image, due to orbital or timing error, will be in first place introduced. A Joint-coregistration approach employing the retrieved shifts of all possible pair combinations will be detailed. A Weighted Least Squares (WLS) estimation is applied to retrieve the azimuth shifts of each image with respect to a selected master image. A stack of Sentinel-1 images acquired in IW mode over Mexico City covering approximately 2 years of acquisitions and eventually other sites is used to evaluate this procedure, comparing its performance to the standard single-master approach. Moreover a validation of the method will be provided highlighting the phase biases that might appear when only a geometric approach or single-master approach are used.