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drastically accentuate even minor relief features. In this
context, the generation of ortho-stereo-partners out of ‘SAR
data might be a deserving task for future radargrammetric
activities.
In an operational mode, topographic radar
stereo-mapping became possible through the employment of
computer-controlled photogrammetric instruments, the
analytical plotters. A complex high-precision software
system for mapping with such a device using single or
stereo-radar images was described by Raggam (1985).
Future work on radargrammetry will be done with images
in a digital format. Hence, digital stereo-mapping systems
- probably together with stereo-correlation techniques -
should be developed to replace analytical plotters and to
support digital topographic mapping (DTM). The acronym DTM,
however, also stands for digital terrain model. The
generation of precise DTMs from SAR stereo-data is one of
the challenging radargrammetric tasks.
In a case study, a digital elevation model of the Mount
Shasta testsite in California was generated from SIR-B
satellite radar data. By means of stereo-radar software,
estimations of the restitution accuracy can be made. It
amounts to approximately 80 meters in planimetry and some 50
meters in height. For SIR-B data, radar- and map-derived
elevation models correspond quite well. In comparison with
previous stereo-models based on SIR-A radar images, which
were evaluated for a first demonstration of the capabilities
of DTM generation with stereo-radar images on the analytical
plotter Kern DSR-1, the results are strikingly better. This
mainly refers to the kind and quality of data digitized at
the stereoplotter. In earlier SIR-A investigations, poly-
gons (drainage and ridge lines) were only digitized with a
point density of about one point per square kilometer, while
for the above-mentioned SIR-B stereo-model contour lines
were selected with a density of digitized terrain points
some ten times higher (cf. Raggam et al. 1985).
4.3 Employment of Radargrammetry for Various Applications
Apart from the importance of incorporating radar-
grammetric procedures for earth-bound applications proper,
the utilization of the various above mentioned approaches
for other disciplines will be necessary.
Due to "the high dependence on a possibly daily
monitoring frequency, aspects of accurate registration and
also of geocoding play an essential role in sea ice
monitoring (ef. Skriver and Gudmandsen 1985). If, however,
image registration should - as proposed - be in the range of
100/200 m, with a desired resolution of 30 m for the planned
ERS-1 sensor, geometric referencing algorithms have to rely
on most precise ephemeris data.
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