This paper presents a nonlocal InSAR filter with the goal of generating
digital elevation models of higher resolution and accuracy from bistatic
TanDEM-X strip map interferograms than with the processing chain used in
production. The currently employed boxcar multilooking filter naturally
decreases the resolution and has inherent limitations on what level of noise
reduction can be achieved. The proposed filter is specifically designed to
account for the inherent diversity of natural terrain by setting several
filtering parameters adaptively. In particular, it considers the local fringe
frequency and scene heterogeneity, ensuring proper denoising of interferograms
with considerable underlying topography as well as urban areas. A comparison
using synthetic and TanDEM-X bistatic strip map datasets with existing InSAR
filters shows the effectiveness of the proposed techniques, most of which could
readily be integrated into existing nonlocal filters. The resulting digital
elevation models outclass the ones produced with the existing global TanDEM-X
DEM processing chain by effectively increasing the resolution from 12m to 6m
and lowering the noise level by roughly a factor of two.