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In section 4.2 some of the benefits of SAR. stereopsis 
are discussed. 
y, SELECTED EXAMPLES OF GEOSCIENTIFIC APPLICATIONS 
4,1 Systematic Investigations on Thematic Image Contents 
Variations of flight and imaging parameters have an 
essential impact on geomorphological terrain feature 
appearance and on the percentage of null-information in the 
image. It is mainly the antenna elevation angle, defined as 
the angle between a vector from the sensor position to the 
nadir and the connection line between sensor and terrain 
target, and the illumination direction, which influence 
these two parameters. 
In order to investigate the influence of varying 
antenna elevation angles, simulated data may be chosen, 
assuming the other system and target parameters to be 
constant. Comparisons between the layover, foreshortening 
and shadow statistics in slant range and in geometrically 
rectified images can then give indications of the usefulness 
of different elevation angles for non-corrected and geocoded 
imagery. Obviously, the loss of information by radar shadow 
("no-shows"), and by layover and foreshortening, where the 
terrain structure can still be viewed, should be differen- 
tiated. Images with large elevation angles, which display 
much shadow, on the other hand even enhance slight geo- 
morphologic structures (cf. Bodechtel 1983), which is 
particularly: helpful "dn flat terrain. A conclusion drawn 
from a study using slant range presentation is that for snow 
and ice mapping in hilly and mountainous terrain optimum 
antenna elevation angles in the range of 40 to 60 degrees 
should be adequate, depending on the percentage of shadow 
and, hence, on the relief. For areas with moderate relief 
40 degrees may be useful, in mountain areas angles around 50 
degrees are preferable (Rott et al. 1985). 
The second geometric parameter, which strongly 
influences the geomorphological evaluation of radar images, 
is the flight/orbit direction relative to the ground. 
In SAR images linear geomorphological structures 
oriented perpendicular to the illumination direction, i.e. 
parallel to the flight path, are strongly enhanced, whereas 
they hardly can be viewed when they strike parallel to this 
direction. Therefore, at least two flights with ‘clearly 
intersecting directions (see below) are needed to provide 
sufficient data for the extraction of all major linear topo- 
graphic features (lineaments; Jaskolla et al. 1985). 
To find out the biases of multi-directional illumina- 
tions, a study in a test area comprising coastal lowlands, 
hilly terrain and mountain ranges has been carried out. 
Under the assumption of ERS-1 imaging parameters (orbit 
327