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APPLICATION OF SHAPE-FROM-SHADING TECHNIQUES TO THE GENERATION OF 
"VALUE-ADDED" INTERPRETATION PRODUCTS OF SAR IMAGES OF RUGGED TERRAIN 
B. Guindon 
Canada Centre for Remote Sensing 
1547 Merivale Rd. Ottawa, Ontario, Canada K2G 4V3 
ABSTRACT 
Spaceborne synthetic aperture radar (SAR) imagery 
is a useful information source for the understand 
ing of the large scale topography of rugged 
terrain because of its radiometric sensitivity to 
terrain orientation. Radiometric variability 
caused by changes in surface cover is generally a 
second-order effect. On the other hand, the 
unique SAR viewing geometry introduces spatial 
distortions (i.e. foreshortening and layover) 
which make it difficult to visually interpret 
physical shapes and sizes of topographic features. 
Because of the predominance of topographic effects 
in both image radiometry and geometry, a research 
program has been undertaken to assess the 
applicability of shape-from-shading techniques to 
the extraction of quantitative terrain information 
from images of rugged terrain. Recent analyses of 
SEASAT images (Guindon, 1989) have shown that 
radiometric response is an accurate indicator of 
the magnitude of the local range component of 
terrain slope. Based on this observation, a 
methodology has been developed which can provide 
both a digital elevation model (DEM) and a 
corresponding image orthoview from a single input 
SAR scene. 
At various stages during the DEM extraction 
process, image by-products can be generated which 
provide quantitative measures of specific terrain 
parameters (e.g. terrain slope maps, drainage 
network overlays). In addition, the DEM-orthoview 
combination can be subsequently employed to 
generate self-consistent image perspective views. 
In short, each product can be considered as some 
form of terrain interpretation, i.e. as a 'value- 
added' interpretation and thereby provide 
additional information for scene understanding. 
In this paper, the shape-from-shading methodology 
is briefly reviewed with emphasis on the deriva 
tion of 'value-added' products and their level of 
accuracy. Example results are provided for two 
SEASAT subscenes of mountainous terrain in central 
British Columbia. 
REFERENCE 
Guindon, B., 1989, Development of a Shape-from- 
Shading Technique for the Extraction of 
Topographic Models from Individual Spaceborne SAR 
Images. Proceedings of the 1989 International 
Geoscience and Remote Sensing Symposium, pp.597- 
602.