Exploring the Potential Pol‐InSAR Techniques at XBand: First Results and Experiments from TanDEM‐X

Abstract

Polarimetric Synthetic Aperture Radar Interferometry (Pol‐InSAR) has been proven to be a powerful radar remote sensing technique for the investigation of natural volume scatterers. The coherent combination of single‐ or multi‐baseline interferograms acquired at different polarisations provides sensitivity to the vertical distribution of scattering processes and allows their characterisation by using the associated (complex) interferometric coherences. However, in repeat‐pass spaceborne implementations, the inherent presence of temporal decorrelation is biasing the interferometric coherence estimates degrading the sensitivity to vertical scattering structure and limiting the performance of Pol‐InSAR inversion techniques. This is the main reason why polarimetric space‐borne missions could not contribute essential neither with respect to large scale demonstration of Pol‐InSAR techniques nor for the development of new Pol‐InSAR applications areas. TanDEM‐X – successfully launched in June 2010 – forms together with TerraSAR‐X the first single‐pass polarimetric interferometer in space. This allows for the first time the acquisition and analysis of Single‐, Dual‐, and Quad‐Pol‐InSAR data without the disturbing effect of temporal decorrelation. Even if X‐band has ‐ when compared to lower frequencies ‐ a reduced penetration capability recent airborne experiments demonstrated several cases where a rather surprising penetration into natural volume scatterers ‐ as vegetation and ice ‐ could be proven. In this sense, the investigation of the Tandem‐X Pol‐InSAR data sets will strongly contribute to our understanding of scattering processes at X‐band and potential new Pol‐InSAR applications. In this presentation, first Pol‐InSAR TanDEM‐X datasets over a number of sites distributed across worldwide are investigated with respect to interferometric volumetric effects in order to provide first insights on the potential of the TanDEM‐X mission for characterisation of natural volume scaterers. For this purpose dual polarimetric (HH/VV and/or HH/HV) datasets from the pursuit monostatic commissioning phase (lasting until September 2010 where both TanDEM‐X and TerraSAR‐X operated in a monostatic mode separated approximately 20km in along‐track that translates in a temporal baseline of approx 3sec.) and the bistatic phase (starting in October 2010 TanDEM and TerraSAR are flying in a close formation and are operated in a bistatic mode with zero temporal baseline) are used.