Digital surface model generation over urban areas using high resolution satellite SAR imagery : tomographic techniques and their application to 3-Dchange monitoring

The urbanization and the management of urban environment and its periphery become one of the most crucial issues in developed and developing countries. In these circumstances, remote sensing data are an important source of information that reflects interactions between human beings and their environment. Given their complete independence from logistic constraints on the ground, illumination (daylight), and weather (clouds) conditions, Synthetic Aperture Radar (SAR) satellite systems may provide important contributions in complex environments 3-D reconstruction. The new generation of high resolution SAR sensors as COSMO-SkyMed, TerraSAR-X and RADARSAT-2 allowed to acquire high resolution SAR imagery. Here the attention is put on the 3-D imaging technique called SAR Tomography: starting from a stack of images collected using multibaseline data performed in interferometric configuration, such a technique allows to retrieve height information forming a synthetic aperture in the elevation direction in order to achieve a substantially improved resolution. The present PhD thesis is focused on the high potentialities of tomographic techniques in 3-D change monitoring and characterization for complex and dense built-up areas using basic mono-dimensional estimators as Beamforming, Capon and MUSIC combined to very high satellite SAR resolution imagery. 2-D and 3-D analysis have been presented over the urban area of Paris using TerraSAR-X data at high resolution and single polarisation. Being mainly focused on the 3-D tomographic techniques, in the presented work 4-D methods, such as compressive sensing (CS), have not been taken into account. At first, the analysis of the interferometric quality of the processed data set has been performed and results showed good mean coherence values within the entire stack. The extraction of 2-D tomograms over different azimuth-profile has showed the capabilities to distinguish more than one scatterer within the same resolution cell and to reconstruct the vertical building profiles. Successively, a global 3-D characterization both in term of buildings heights and vertical reflectivity has been performed in order to develop a monitoring tool for the changes of single structures. Moreover, the possibility to correct the geometric distortions due to the layover (that strongly affects such kind of scenarios) and to determine the information about the number of scatterers (up to three) and the corresponding reflectivity within one resolution cell have been evaluated. Moreover an innovative time stability analysis of the observed scene have been carried out in order to detect the stable and unstable scatterers. Globally, the investigations showed noisier and sparser point clouds for the Capon method, whereas better capabilities for the Beamforming and MUSIC ones. Indeed, it was possible to detect different scatterers located within the same resolution cell and to resolve pixels affected by the layover. This has lead to perform a good reconstruction of building shape and location and a good estimation of their elevation. The 3-D time stability analysis demonstrated the possibility to monitor the 3-D change depending on the time. Eventually, it is possible to assert that processing high resolution SAR data allows to achieve a strong improvement in 3-D imaging capabilities. It has been demonstrated the potentialities of TomoSAR technique in distortions correction and in 3-D change monitoring using basic mono-dimensional estimators.