855 
)rmation 
depression angle. The areas of radar shadow are entirely black. Radar shadow 
that shown 
length increases with relief but also with a decrease of depression angle from 
;tation 
near to far range. 
1). This 
of 
3.1 High relief areas 
ructurally 
3 copic 
ap the 
The radar shadow area was measured for a high relief area in the Eastern 
Cordilleras of Colombia (Sierra Nevada del Cocuy, 5493 m). The area was flown 
o 
with X band radar, flight elevation, 12,500 metres. Of an area of 184 km , 52,6% 
of the total was measured as shadow area. This means that no information at all 
was obtained from 52. 6% of the area. 
mages, 
Flying with opposite scan directions over the same area makes it possible to 
illuminate opposite topographic slopes. Relief displacement in the area is con 
siderable. It was found that drainage delineation on monoscopic radar interpre 
tation had very little resemblance with that from the topographic map (MOSQUERA, 
or more). 
pers. comm.). Comparison with stereoscopic imagery was not possible due to lack 
of overlapping strips, but from experience elsewhere it is unlikely that good stereo 
vision can be obtained in such high relief areas (KOOPMANS, 1974). 
dense 
3.2 Medium relief areas 
ter sur 
Areas were selected between Salt River and Superior (Arizona). A comparison 
rest 
was made between monos copic interpretation of far range and near range imagery. 
is ob- 
One drainage area was situated sloping mainly towards the scanner, the other away 
' relief 
from the scanner. For the first area the detail on the far range image was higher 
nd X 
than that on the near range image. 
neglected. 
.sis of 
This is mainly due to the "blooming'' effect and less shadowing as a result of the 
nearly perpendicular incidence angle which obliterates minor density differences 
ver 
on the image in the near range. On the other hand the second area shows more 
iia), or 
detail in the near range where the incidence angle is very small, allowing for 
relief differentiation. 
ow, which 
In the far range, much of the area is situated in radar shadow. Without taking 
g towards 
radar 
stereo viewing into consideration it can already be realized that two passes over 
the same area in the far and near ranges already offer advantages of more detail 
shadowing 
es, other- 
than just one pass. The three dimensional picture allows the observation of rela 
tive altitude differences often not visible monoscopically. One should realize that 
no stereoscopy is obtained for those areas within the radar shadow on one of the 
within 
images. One eye will see the black shadow area, whereas the other eye may see 
an the 
detail on the other image of the stereopair. The overriding blackness on one eye