  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 large-stack
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 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.
