  Multi-baseline interferometric synthetic aperture radar (InSAR) techniques
are effective approaches for retrieving the 3-D information of urban areas. In
order to obtain a plausible reconstruction, it is necessary to use more than
twenty interferograms. Hence, these methods are commonly not appropriate for
large-scale 3-D urban mapping using TanDEM-X data where only a few acquisitions
are available in average for each city. This work proposes a new SAR
tomographic processing framework to work with those extremely small stacks,
which integrates the non-local filtering into SAR tomography inversion. The
applicability of the algorithm is demonstrated using a TanDEM-X multi-baseline
stack with 5 bistatic interferograms over the whole city of Munich, Germany.
Systematic comparison of our result with TanDEM-X raw digital elevation models
(DEM) and airborne LiDAR data shows that the relative height accuracy of two
third buildings is within two meters, which outperforms the TanDEM-X raw DEM.
The promising performance of the proposed algorithm paved the first step
towards high quality large-scale 3-D urban mapping.
