In: Stilla U, Rottensteiner F, Paparoditis N (Eds) CMRT09. IAPRS, Vol. XXXVIII, Part 3/W4 — Paris, France, 3-4 September, 2009 
along the elevation direction. It is located at the layover area. 
Fig.9 gives a closer look to the ground truth at that area. The 
left image shows the convention center visualized in Google 
Earth in which the pixel of interest is included in the area 
marked by a red block. The right image tells that the returns 
from the roof of the convention center and from the plaza near 
ground mainly contribute to the measurement of this pixel. 
Figure 8: TerraSAR-X intensity image of convention center, 
Las Vegas; selected pixel marked by green spot 
Figure 9: corresponding aerial image, © Google Earth 
Figure 10: Model of the ground truth for the pixel of interest 
For simulation, we simplify the ground truth to the following 
model as depicted in Fig. 10. The incidence angle for the 
acquisition is adapted to the real SAR acquisition and, hence, is 
31.8 degrees. The taller building refers to the convention center 
which has a height of about 24m, while the lower building 
stands for the plaza near ground. Heights are measured over 
ground. The measurement for the pixel of interest refers to the 
integral of the returns from the objects included in the strip 
highlighted in blue color. For simulation purposes, two box 
models are used for modeling both the plaza and the convention 
center (Figure 11). The roughness of the plaza’s surface is 
assumed to be slightly higher than the roughness of walls and 
roof parts of the convention center. 
3.2 Simulation vs. real data 
The reflectivity profile of the resolution cell along elevation 
direction is derived using the simulation concept described in 
Section 2. Pixel selection is adapted to extracted real data as 
shown in Figure 8. Afterwards, the resulting slice in elevation is 
displayed in height over ground geometry (Figure 12). Heights 
of reflecting objects are reliably extracted as two single bounce 
contributions at heights of 3 and 24 meters. 
Figure 11: 3D model scene containing two boxes for 
approximating layover effect (flat box: 20 m x 30 m x 
3 m; tall box: 15 m x 15 m x 24 m); diffuse 
backscattering behaviour at all box surfaces 
Figure 12: discrete elevation coordinates for backscattering 
objects; step-width in elevation: 1 meter 
Fig. 13 shows the result of tomographic analysis for the 
corresponding position in real TerraSAR-X data. The reflection 
profile has been calculated with the approach described in (Zhu 
et al., 2008). As input data, 16 TerraSAR-X spotlight images 
with an across-track baseline range of 270m have been used. 
The peaks in reflection profile show nice correspondence with 
the simulated results, which underlines the accurate geometric 
properties of the simulation. However, it has to be noted that 
accurate estimation of intensity proportions is not possible as 
ground truth for surface properties was not available. At this 
point, simulated intensity values only indicate a stronger diffuse 
backscattering from the plaza which is also visible in the 
reflectivity map extracted from real SAR data. Enhanced 
information about the scattering behaviour of the plaza and the 
convention center may enable better simulation results in the