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Stilla, Uwe

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