ERS-ENVISAT Permanent Scatterers

The phase time series of a perfect point-wise Permanent Scatterer (PS) would show a phase jump passing from ERS to ENVISAT SAR images. A PS analysis has been carried out on a dataset including both ERS and ENVISAT images. For each PS, elevation, LOS velocity and phase jump have been jointly estimated and removed, allowing the identification of the atmospheric phase screen. The PS population so found represents the intersection of ERS and ENVISAT PS populations. The probability of natural targets to behave as PS both in ERS and ENVISAT has been analyzed as a function of their Radar Cross-Section, acquisition geometry and amplitude. Distributed targets with a narrow backscattering lobe pointed towards the first sensor (ERS) are not coherently observed by the second one (ENVISAT), whereas point-wise targets (e.g. natural corner reflectors, dihedrals and small mirrors) will remain coherent in both cases. Experimental results have been carried out on a data set of 69 ERS images and 7 ENVISAT images (ERS-like mode) on Milano over a 20 km side area.