7000 4 
6000 + 
5000 4 
4000 .- 7 
3000 + 
. No of obs 
2000 + 
M 
1000 - 
  
sl 
Sess 
  
  
  
  
  
  
  
50 100 
Histogram - ASPECT 
A A A A A 5 
x A 
AC 23 
150 200 250 300 350 
ASPECT DEGREES 
Figure4b. The histogram of the aspects on Fig.2a. Flat - horizontal area is marked by 361. 
All 25 cells have aspect in azimuth angle interval from -46? 
to 56°, and slope angles from 6°to 50°. If SAR has position 
northern to considered region R, mentioned cells could be 
seen as they have in this direction the fore slopes only. By 
generalizing we can derive criteria for determination of the 
SAR route space V, with minimum loss due to shadows: 
a) All DEM cells of the region R, whose aspect angle (y 
belongs to the azimuth's interval 
in which volume V could be seen from the most angularly 
distant cells in region R, could be imaged by SAR with no 
losses caused by the shadows, 
b) All DEM cells which have aspect angles in the interval of 
azimuths 
À min+180° < Q« O0 uum, (3) 
thus being backslopes in case (a), could be imaged by SAR 
if the their slope angle € satisfies relation 
(&* V) € d (^4 ) e 
where y is minimum allowable grazing angle (usually 
4°), d (Hd) is minimum depression angle for the SAR 
antenna in the vertical plane, at distance d, H is SAR 
altitude. 
c) For other cells, which are not contained in cases (a) and 
(b), considered volumeV has loss due to shadows, and new 
volume V' is to be selected, according to (a) or (b). 
According to these criteria, the problem of the route 
determination without the loss due to shadows could be 
solved by some of the numerical finding the extreme 
methods. The whole area around the terrain limited by 
maximum aircraft altitude H is considered. Conditions 2), 
3) 4) can be tested by supervised classification. Fig.6 
illustrates the application of criteria 2), 3) and 4). 
  
  
  
  
  
  
0 i 2 
Figure 6. Classified fore slopes for azimuth angle mean 
53.56°, standard deviation 34.69> backslopes for azimuth 
angle mean 230.65? , standard deviation 70.65°. 
Corresponding slope angles have mean 9.96° and 9.14? 
respectively. For considered angles there are 32.68% 
foreslopes and 67.32 % backslopes. a) Classified image. b) 
Legend. In color. 
514 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 
  
  
  
  
  
  
  
  
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appro: