This paper presents the fusion of monostatic repeat-pass and bistatic single-pass SAR data in complex urban environments to improve the results of stacking techniques such as Persistent Scatterer Interferometry (PSI). Addition of a few motion-free and atmosphere-free TanDEM-X data pairs to the existing TerraSAR-X data stack can improve the 3D positioning and deformation monitoring of objects. However, in dense metropolitan areas, the standard TanDEM-X elevation models are inaccurate because of geometrical limitations such as radar layover. In this paper, the potential of jointly processing TerraSAR-X and TanDEM-X data for resolving single or double scattering mechanisms present in the same resolution cell has been investigated. The technical details and demonstration are provided using high resolution spotlight mixed TerraSAR-X /TanDEM-X data of Las Vegas, US.