Full text: CMRT09

In: Stilla U, Rottensteiner F, Paparoditis N (Eds) CMRT09. IAPRS, Vol. XXXVIII, Part 3/W4 — Paris, France, 3-4 September, 2009 
Eventually, the simulation process provides the following 
output data for each reflection contribution detected in the 3D 
object scene: 
• coordinates in azimuth, slant range, and elevation 
[units: meter] 
• intensity data [dimensionless value between 0 and 1] 
• bounce level information for every reflection 
contribution [1 for single bounce, 2 for double 
bounce, etc.] 
• flags marking specular reflection effects [value 0 or 
Figure 2: left: Simulation using box model having a size of 20 
m x 20 m x 20 m, line of sight indicated by arrow; 
right: simulated reflectivity map simulated (slant- 
range indicated by arrow) 
Figure 3: simulation using step model (left), line of sight 
indicated by arrow; simulated reflectivity map (right), 
slant-range indicated by arrow 
2.3 Reflectivity maps in azimuth and slant range 
Firstly, all reflection contributions are mapped into the azimuth 
- slant range plane. Afterwards, a regular grid is imposed onto 
the plane and intensity contributions are summed up for each 
image pixel. Figure 2 shows the resulting reflectivity map for a 
cube (dimensions: 20 m x 20 m x 20 m) which has been 
illuminated by the virtual SAR sensor using an incidence angle 
of 45 degrees. The size of one resolution cell has been fixed to 
cover 0.5 m x 0.5 m in azimuth and slant range. Surface 
parameters are chosen in a way that box surfaces can be clearly 
distinguished from ground parts, i.e. in the current example box 
surfaces show stronger diffuse backscattering than the 
surrounding ground. Following top-down in ground range 
direction, diffuse single bounce contributions of the ground are 
visible followed by a layover area of ground, wall of the box 
and top of the box. At the end of the layover area, a strong 
double bounce line is visible which is caused by the interaction 
between the front wall and the ground in front of the box. 
For this type of scene geometry, a 2D simulation and analysis is 
usually sufficient. The next section will however illustrate 
examples that underline the necessity of including the elevation 
direction as third dimension into the simulation. 
Figure 4: selection of pixel for elevation analysis (left); 
definition of three slices (right) in slant-range (1), 
azimuth (2), and elevation direction (3) 
2.4 3D analysis of scattering effects 
Figure 3 shows a reflectivity map simulated by illuminating a 
step model (width: 10 m, length 20 m, height 20 m). For 
providing the map, the same imaging geometry has been chosen 
as for the box example, i.e. the step was oriented in direction to 
the sensor and the incidence angle was fixed to 45 degrees in 
order to obtain specific overlay effects for single and double 
bounce contributions which are explained in the following. 
Compared to the reflectivity map containing the box model 
(Figure 2), the reflectivity map of the step shows similar 
characteristics. Both the layover area of single bounce 
contributions and the location of focused double bounce 
contributions are identical. Only the size of the shadow zone 
indicates a height difference between the illuminated objects. In 
the case of the step model, separation of dihedrals - two right 
angles at the steps - is impossible in the reflectivity map since 
all double bounce effects are condensed in one single line. 
Hence, separation of scattering effects in elevation direction 
may be helpful since it enables to resolve layover effects for the 
purpose of distinguishing several scatterers within one 
resolution cell. To this end, an interactive click-tool has been 
included into the simulator for defining two-dimensional slices 
to be analyzed. In the case of the given reflectivity map for the 
step model, one pixel is selected, e.g. located in the double 
bounce area as shown in Figure 4. Based on the coordinates of 
the pixel center, three slices are defined: 
• slice no. 1 for displaying elevation data in slant-range 
• slice no. 2 for displaying elevation data in azimuth 

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