# 3D Monitoring of Buildings Using TerraSAR-X InSAR, DInSAR and PolSAR Capacities
## 6 Conclusions  
A careful analysis of a TerraSAR-X dataset over urban area has been presented in this article. The major assets of this sensor for urban area are its fine resolution and its agility enabling to acquired images in different modes. The studied dataset combines 98 for InSAR/DInSAR images acquired during four years and two PolInSAR acquisitions. Using this dataset we could quantify the contributions, as well as the underlying difficulties, of each mode. Concerning the updating of building elevations, we showed that the repeat-pass InSAR mode leads to a coherence high enough to use the interferometric phase on the buildings, even with three years separating the acquisitions. However, more than one repeat-pass pair is needed to get reliable  
Figure 17: Results of estimation of polarimetric orientation for the Tour Eiffel, compared with orientations of main beams, for stable orientations. Figure 18: Difference of (**a**) diattenuation and (**b**) retardance for the five different buildings. height estimated since even the slight daily building deformations can have a great impact of elevation measurement. We have proposed an efficient method to make the height measurement more robust by using the entire time series. Thanks to this sensibility to buildings deformation due to the TSX wavelength and resolution, we have also demonstrated that it becomes possible to use the DInSAR mode to monitor the building deformations. This has been done without making any assumption on the deformation processes. This was particularly useful to estimate non-linear deformations, such as for the Eiffel Tower, whose deformation behavior is very complex to model. For the Eiffel Tower, we measured deformation up to 4 cm over the time series and we estimated deformation about 1 cm for the three other studied buildings. Our deformation estimations were compared with local in situ measurements and were of the same order of magnitude. Our estimations were also correlated to weather data. This validation has proven that a centimeter precision can be achieved even when neglecting the atmosphere. It has also shown that building deformation patterns observed differ widely between profiles. Finally, we have investigated the benefit of the polarimetric mode for building monitoring. As in previous study, the polarimetric coherence optimization has been proven to be very effective to increase the coherence level. Nevertheless, the small polarimetric dataset and the small ambiguity height limit the use of the interferometric phase for repeat pass deformation measurement. In order to measure information about the geometry and the materials from polarimetric images, the deterministic analysis seems to be appropriate. Indeed, at this wavelength and resolution range, polarimeter signals are stable among time but are not reproducible between neighboring pixels. The polarimetric return is large part dominated by orientation effects. We have shown that the orientations of the main attenuation axis are very well correlated with the orientation of the vertical facades with respect to the azimuth axis. Results are still limited by the resolution loss in the polarimetric mode, but are encouraging for future sensors. Indeed, the gains made by the increasing resolutions, already demonstrated in the single-pol modes, make it possible to envisage polarimetry for new kinds of applications: geometry and complexity of facades and structures. This paper provides some reasons to be optimistic for the use of X-band very high resolution sensors for measuring and analysing the deformation of the structures. To improve the resolution scale of the deformation estimation, single-pass mode and repeat-pass mode could be combined. Deformations for every resolution cell at the different elevations of the buildings could be estimated, taking fully advantage of the TSX resolution. Ground and building deformations could thus be separated.