Thomas Damaseaux 
  
The height of a point P (cf. Figure 2) can then be derived from A , by 
hzH-(r, *A,)cos 0, (2) 
H denotes the altitude of antenna S2 above the geoid. 
Another helpful feature of InSAR is the evaluation of the coherence. The coherence gives a measure of how 
identically the backscatter signal is returned to the antennas. Considering targets with a volumetric scattering 
effect, the backscattered signal of the two antennas will be not identical, i.e. the phase without the contribution 
of A , and amplitude are not exactly the same, causing a decrease in the coherence. The coherence is defined as: 
N * 
Sc UO e cum 
n-l 
     
  
  
>> 
Il 
(3) 
N 
es 
n=l 
where c,, = complex 2 dimensional images of the antennas 1 and 2; N = number of averaged samples 
a)? CUR 
en cl” 
N 
> 
n=l 
  
  
  
  
3. Processing chain from raw data recording to topographic map 
Figure 5 gives overview of how a topographic map is derived. The raw data recording is followed by the SAR 
and interferometric processing. The geocoding results in a DEM, an ortho SAR image and an ortho coherence 
image. These results are also called primary features. The step of information extraction then leads to a 
classification result, contour lines and finally to a topographic map. 
ee 
  
  
  
= SAR Processing | 
Image gi | Image 2 
Interferometric 
Processing 
i | 
| Phase | | Coherence | 
| : 
Geocoding and 
Radiometrie 
rrr | 
  
  
  
  
  
  
  
  
  
  
     
SAR Image Coherence 
>>> 
Information Extraction 
pee n qid boo TG 
fiho, UR: 
  
  
  
  
  
     
Classification Contour Lines Top. Map 
Figure 5. The processing chain from raw data to topographic map 
  
56 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000. 
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