ES BT LL A FLARE Rae 
Relation (1) shows that the shadow width grows with the 
growing distance d and the obstacle elevation h what should 
be taken into account when the terrain is analyzed. Model of 
the obstacle and shadow from the Fig. 1. can be applied to 
some area presented by means of digital model of the relief 
elevation - DEM (Davis J.C., McCullagh M.J,, edit., 1975). 
First, slope is calculated from DEM and aspect of every 
DEM cell (Horn B.K.P., 1981). The following is the picture 
of DEM for the considered area, Fig.2a, the elevation 
histogram Fig.2b. The image of the slope for considered 
terrain is shown on Fig.3a, and the histogram on Fig.3b. 
Image of the aspect angles is shown in Fig4a, and the 
corresponding histogram in the Fig.4b. 
  
  
Figure 2a. DEM for the considered area. Black - minimum 
elevation, white - high elevation. (Original DEM elevation 
data are 16 bits, image on Fig.2a. shows limited range of 
elevations). 
  
Figure 3a. Image of the slopes of the terrain on Fig.2a. Black 
- 0°, white - 64°. Streched intensity, compare histogram on 
Fig. 3b. 
SE OR ARR AIME EEE A tree A PONS naar EEE 
  
Figureda. The aspects of the terrain in Fig.2a. Black - 0° 
(Nord), white - 359^. 
Histograms for Fig.2a, Fig3.a and Fig.4a are shown on next 
page. 
The possibility to enhance the terrain features causing the 
shadows by the classification methods is analyzed. If slope 
and DEM elevation are used as two sorts of data for 
classification then the enhanced structure contributing most 
to generating the shadows is obtained. This makes the 
possibility to establish the existence and position of 
geomorphologic structures causing the shadows without 
either SAR images or SAR images simulation (based on 
DEM). However, this is not enough because it does not say 
anything about the loss. Therefore, criteria to enable this are 
introduced in the next passage. 
4. CRITERIA FOR THE DETERMINATION OF AN 
AIRBORNE SAR ROUTE WITH MINIMUM LOSS 
DUE TO SHADOWS 
Data on aspects and slope enable the calculation of the 
airspace around some considered area R, within which the 
foreslopes and backslopes of all obstacles can be imaged. 
The imaging can be from the other side of those parts which 
cannot be imaged from the front side. The example of the 
data for aspect and slope angles, for 5x5 cells of the upper 
left part of the DEM Fig2a, is shown in Fig. 5. 
  
+56 +32 +353 +331 314 
a Er 4332 
50:926 +359 +4 
+23 26 +8 +355 +351 
+48 42; 4355 . 347. +338 
  
  
  
  
  
  
a 
08 13.21 25 20 
15 23 LÉ] 25 2 
6 41 20 29 
33.34 90.42 37 
47 23 42 48 39 
b 
Figure 5. An example of the a) aspect and b) slope data, 
for 5x5 cells in the upper left comer of the DEM from 
Fig.2a. 
512 Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998