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(b) 
Figure 7: The layover maps from Fig.6 after matching. Cor- 
responding match points were assigned the same gray value. 
by stereo intersection. The obtained relative height values 
were then adjusted by an offset, in order to compare them 
with the corresponding reference DEM. The result is shown 
in Fig.8, where terrain elevations in active layover areas are 
encoded as gray values. Elevations in the displayed areas 
range from about 2500 m to 3700 m. In the central part of 
the image, both the shape and the height of the reconstructed 
regions in (a) correspond well to the real terrain in (b). The 
arrow in Fig.8 (a) denotes an area with layover regions that 
are separate in one stereo image, but joint in the other one 
(see Fig.7). Note that the reconstructed active layover areas 
in Fig.8 are also separated, which means that this situation 
was properly recognized by the matching algorithm. 
4 SUMMARY AND OUTLOOK 
We presented a concept for the detection and use of lay- 
over information in Magellan SAR imagery. The simulation 
Program and matching algorithm described in the previous 
section constitute a first step towards the automated terrain 
287 
(b) 
Figure 8: Terrain elevations in active layover areas recon- 
structed from match points (a) in comparison with the cor- 
responding real terrain (b). 
reconstruction in foreshortening and layover areas, as well as 
the distinction between them. The matching results obtained 
from tests on simulated layover maps are encouraging. As a 
next step, the matching algorithm will be applied to Magel- 
lan stereo images, and the results will be compared to the 
manual measurements carried out by [Connors, 1994]. Then, 
the DEM derived from same-side stereo images will be input 
to the simulation program, in order to generate a synthetic 
image which resembles the corresponding opposite-side SAR 
image. The simulated image is expected to facilitate the iden- 
tification of corresponding features in dissimilar SAR images, 
which is a prerequisite for resolving the remaining ambiguity 
between foreshortening and layover. Although the aim of the 
current study is the development of new algorithms for the 
topographic surface reconstruction from Magellan imagery, 
the results obtained in this context are not limited to this 
particular data set, but will also be applicable to other SAR 
data from both planetary and terrestrial missions. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996