Persistent scatterers at building facades – Evaluation of appearance and localization accuracy

Thanks to the high resolution of modern SAR satellites many persistent scatterers (PS) appear at single buildings. Approximately half of them represent building facades. These groups of points often show regular patterns in SAR images that can be related to repeating structure elements on the facades. Hence, individual buildings can now be monitored over time, either based on amplitude (for change detection) or phase information (using interferometric methods). However, patterns of point signatures are often disrupted or disappear when the imaging geometry is slightly changed. In addition, the localization accuracy of estimated and geocoded natural PS is not known, yet. The investigation at hand provides a detailed analysis of PS patterns based on reference data obtained from a photogrammetric survey and terrestrial measurements. The processing of the optical images allows creating a detailed 3D model of the respective facade, which represents the geometrical object information for SAR simulation. The terrestrial measurements allow relating the 3D model to its true position in a world coordinate system like UTM (Universal Transverse Mercator), which is necessary for assessing the localization accuracy of the signatures. From the simulation results the appearance of the point patterns of natural PS in high resolution SAR data can be better understood. Moreover, the localization accuracy and the precision for these points can be derived for the first time. The approach and findings for two case studies in Munich are described in detail in this paper.