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the same height from near range to far range, providing an exaggerated relief 
impression in the far range. 
Since 1967 SLAR surveys over large parts of the humid tropics have provided a 
wealth of imagery for thematic mapping. Many of these surveys have been flown 
only with a limited sidelap of consecutive radar strips, making stereo viewing 
impossible. To obtain a stereo image a 60% sidelap is desirable. This at least 
doubles the amount of flight kilometers to be flown as well as the amount of radar 
strips to be obtained. Do the advantages of stereo radar in thematic mapping 
justify the extra expenditure for the survey? The author is of the opinion that for 
most areas, with exception of very high relief areas,the answer will be yes. 
Apart from the future possibility of development of radargrammetric instrumentation 
for precision mapping using stereo radar, approximate measurements can be made 
for purposes of thematic image interpretation (LEBERL, 1973). For thematic map- 
ping,better results are obtained from stereo radar than from monoscopic studies 
of radar images,especially for low relief areas. 
MEASUREMENTS FROM SINGLE STRIP AND STEREO SLAR IMAGERY 
Measurements from single strip imagery 
Radar shadows on single strip imagery give the interpreter a relief impression of 
the terrain. The imagery should be oriented in such a way that the radar shadows 
fall towards the interpreter. With an opposite orientation of the radar image an 
inverted relief impression is obtained. From the shadow length,relative altitude 
differences may be obtained from single strip imagery (LA PRADE & LEONARDO, 
1969). With decreasing depression angle the shadow length of a particular object 
will become larger. This depression angle will vary with flight altitude but also 
with distance from flight line to object when using a determined flying height. The 
depression angle will decrease from near range to far range throughout a strip. 
Representation of the radar image might be in slant range or ground range repre 
sentation. In the first large commercial SLAR survey over Panama in 1967, 
(CRANDALL, 1969), slant range representation was used. Since then, most of 
the commercial surveys have been carried out in ground range representation, 
the image of which gives a much better geometric, more or less orthogonal pro 
jection. The relation between slant range and ground range is: 
Rs 
( 1 ) 
in which Rs is the slant range, Rg is the ground range, and H is the flight altitude 
(fig. 1). The nomogram developed by RYDSTROM (1968) allows for the rapid