# 3D Monitoring of Buildings Using TerraSAR-X InSAR, DInSAR and PolSAR Capacities
## 5 Polarimetric Analysis
### Benefit of Polarimetry for Building Monitoring
#### 5.2.3 Results  
We present now the orientation distributions found over main fronts of our five buildings, and compare them with the true orientations found for horizontal elements of the walls. First, results obtained on the Mirabeau Tower are shown in Figure 14. Five different facades with different orientations are visible on the image. Resulting orientation angles are very well correlated with our ground truth, represented by the red arrows in the charts, and by the colored representation of the 3D model. They show clearly the influence of facade orientation respective to azimuth direction. The orientations have been computed for the four polarimetric images. They do not differ a lot from one polarimetric to the other one, except for the wall exactly aligned with the azimuth. Only in this case, small differences can be noticed between the strictly monostatic acquisitions, and the quasi-monostatic ones where transmitter and receiver belong to the two different sensors TSX and TDX. Note that the facades are not strictly plane, as the picture shows: the faces therefore have a variability of orientations that can explain the variance of our estimates. Espace 2000 and Keller Towers  
In Figure 15, we analyze two different buildings, the Espace 2000 Tower (Building 5) and the Keller (Building 3) Tower which facade have very similar global orientations, but different scattering. Estimations made on the Keller Tower show that both facades include the two main orientations found in the ground truth. The facade photo reveals that window frames include both directions. They are probably the cause of trihedral effects and could explain the strong signal scattered by this building. In any case, both main directions are retrieved in the polarimetric angle estimation. Orientation values estimated over the Espace 2000 Tower are more dispersed. Picture reveals that the small balconies have much more complex shapes. Principal orientations remain, but with more variability. Perspective II and Cristal Towers  
Figure 16 shows results for more complex buildings: the Perspective II and Cristal towers. Once again, the main orientations are retrieved. The Cristal tower is the one that generates the bigger variability. This is probably due to the fact that the Cristal tower has also a very low backscattered signal, because it is made on glass that exhibits a very high absorptivity at X-band. Thus, the estimation of the orientation is very noisy. For Perspective II, one of the privileged orientations is found for both main facades. Figure 14: Results of estimation of polarimetric orientation for the Mirabeau tower. Eiffel Tower  
For the Eiffel Tower, orientation effects are very chaotic. The structure is very difficult to describe, and as mentioned previously, polarimetric return is hard to anticipate. We have thus restricted comparison with ground truth to pixels whose estimated orientation are very similar among the four acquisitions. To check this point, we have computed the second circular statistical moment to select only pixels whose orientation homogeneity is at least 80%. At a coarse scale, these estimations are correlated to those of the ground truth. Results are shown on Figure 17.  
Finally, diattenuation and retardance have been computed. They are represented in Figure 18. Retardance is very sensible to the parity of number of bounces involved in the scattering process. It shows that the facade of the Mirabeau tower aligned with the azimuth involves a lot of local double-bounce scattering on the windowsills. These double bounce mechanisms disappear when an angle is introduced between the facade and the azimuth axis. The value of the diattenuation differs even for buildings having the same general orientations. This difference may be due either to differences in materials and permittivity, or to differences in local geometries in structures. Figure 16: Images of the buildings and detail of its facade, orientation of the facade from the ground truth and results of estimation of polarimetric orientation.