847 
ssed in 
( 2 ) 
(3) 
aphic 
ross the 
¡ssion 
l AgC in 
(4) 
(5) 
md range, 
•ession 
d BC. 
er 
the 
lay-over, the sum of shadow length and lay-over length will be the length AgC of 
fig. 4 and equation 4 can be used to find the corresponding height. This shifts the 
problem, however, to differentiating lay-over from a highly foreshortened slope 
in an image. Recognizing lay-over on the radar image has been found to be ex 
tremely difficult in practice in areas with relief. Where a foreshortened slope is 
measured erroneously as lay-over a considerable error will be introduced in 
height determination. 
Especially with the larger depression angles the difference between the equations 
2 and 4 will incease. A radar shadow of 10 mm length, on for example images of 
a scale 1 : 100, 000 will represent a height of approximately 176 m for a vertical 
object scanned under a 10 degree depression angle and a height of 1000 metres 
where the depression angle is 45 degrees. For a topographic slope using equation 
4 these amounts are respectively 171 m and 500 m. 
10 20 30 40 50 60 
depression angle © 
Fig. 5a 
Height depression angle relation for 
a vertical object and a topographic slope 
(<T<comp Q ) for a measured shadow 
length of 10 mm on the image scale 1:100, 000 
Fig. 5b 
Shadow length-depression angle relation for 
a vertical object and a topographic slope. 
(a < comp 0 ), the object and slope having 
a height of 200 m, image scale 1:100, 000. 
In fig. 5a the height-depression angle relation is given in the dashed curve for a 
vertical object with a radar shadow length of 10 mm. The full drawn curve gives 
the height-depression angle relation for topographic slopes dipping under an angle 
which is smaller than the complement of the depression angle, again for a shadow 
length of 10 mm. It can be seen that the differences between height determination 
by equation 2 and equation 4 for depression angles greater than 30 degrees become