With reference to the type of the initial coordinates,
in the first case the transformation is accomplished by a
so-called "object space algorithm", in the second by an
"image space algorithm".
2.1 Map-to-Image Registration
By applying the object space algorithm, cartographie
information can be displayed in an original SAR image. A
three-dimensional digital map, which may be taken as a
digital landscape model, is created. by bringing a digital
terrain model (DTM) into a defined cartographic projection,
using two-dimensional data (linear and aereal features)
derived from topographic and/or thematic maps. The above
transformation is then used Lo. obtain ‚registered. map
overlays (Lukes and Raggam 1986), which could then easily be
retransformed into the object space.
Map-to-image registration plays a role in all
applications, which are sensible to grey value changes due
to geometric corrections, e. ge geocoding, and where
therefore the experts favourably want to. evaluate the
unchanged SAR imagery. Potential fields of employment of
this procedure are the general task of map-guided data
acquisition from. SAR .image. and, in. particular, earth
resources exploitation requiring frequent monitoring.
It certainly is a deserving task to extend this idea to
three-dimensional thematic data that can be compiled from
any type of stereoscopic remote sensing data, e. g. using
an. analytical plotter, though without in the first instance
having the data linked to a defined cartographic projection.
SAR Image Simulation
Another important utilization of the radargrammetric
model lies. in. the possibility. to .transform the digital
landscape model as a whole or in parts into the image space,
thereby creating a synthesized SAR-like image. In order to
obtain an image displaying realisitic grey values, a
radiometric model capable to incorporate backscatter
variations due to different surface types and speckle noise
appearance is needed. The process comprising these elements
is known as SAR image simulation.
Due to the complexity of radar physics, the radiometric
models are still far from providing a sound basis for true
image intensity simulation. In a number of investigations,
the reconstruction of the mapping geometry is indeed the
ma jor aspect, whereas the correct representation of surface
signature and speckle is less significant. On the other
hand, simulation can be a useful tool: .to. . analyze the
radiometric properties of a real SAR image:
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