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The incidence angle of the radar beam component at the 
ground element can be reconstructed, and .the angular 
dependency on backscatter derived. Based on this 
information, a SAR image can be radiometrically corrected 
with respect to terrain relief influences on the pixel grey 
values. 
Layover and shadow areas, which only contain contorted 
or indirect information, can be numerically determined and 
coded, so that they can be excluded from or weighted in 
evaluations relying on statistical grey value information. 
2.2 Image-to-Map Registration 
The aim of this geometric approach is to generate a 
radar image which is geometrically independent on the SAR 
imaging process (removal of geometric distortions), and in 
doing so, transform the image into the geometry of a 
selected map projection. Moreover, the correct positioning 
parameters of the image within a global map coordinate grid 
have to be identified. 
The final product of this process can be referred to as 
a geocoded image, or, if the reference map shows an 
orthogonal projection, as an ortho-image. 
In fact, geocoding is performed by a complex multi-step 
process which has been addressed in a paper by Domik et al. 
1984, and is still a subject of comprehensive investigations 
(Raggam et al. 1986). For the ease of reference a brief 
description of two alternative principles for geocoding is 
given in the following. 
Geocoding Based on Simulation 
Simulation techniques can be used to transform small 
object space segments ("chips") from a data base containing 
selected topographic and thematic features into a 
specifiable SAR image geometry. Criterion for the selection 
of these chips is a good and possibly automatic geometric 
comparability of the simulated chip and the homologue 
feature in the SAR image. Residual location differences 
between simulated and real feature measured in the image 
space are used to determine the coefficients of a polynomial 
relative rectification of the real image. In this 
procedure, the real image is transformed into exactly that 
SAR image geometry which is consistent with the 
radargrammetric model. Eventually, the image-to-object 
space transformation and subsequent resampling yields the 
geocoded image product. 
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