Title:
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Investigation of Seasat : a synthetic aperture radar (SAR) for topographic mapping applications
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The thesis is concerned with an investigation of the possibilities
of generating metric information and carrying out topographic
mapping operations from side-looking radar images acquired from Earthorbiting
satellites, as exemplified by the synthetic aperture radar
(SAR) system flown onboard the Seasat satellite, Besides the
theoretical analysis of the problem, several images covering test areas
with different topographic characteristics have been used for extensive
and comprehensive tests of the geometric accuracy of the SAR system;
for experiments with digital monoplotting techniques applied to the SAR
images; and for tests concerned with the detection and"interpretation
of objects appearing on these images.
The results show that metric information of a limited accuracy
can be obtained from satellite SAR images. This could act as the
basis for reconnaissance-type mapping at scales of 1: 250,000 and smaller.
The geometric accuracy actually achieved does, however, depend heavily
on the method used initially to process the SAR image data. In this
respect, the results obtained with the digitally processed images are
superior to those obtained with the optically processed images. The
influence of the topographic relief present on the ground is also
noticeable and various techniques have been devised and used to eliminate
or substantially reduce this effect.
The use of digital monoplotting techniques did not produce as
good or as complete a rectification as expected due to the difficulties
experienced with the interpretation of the terrain objects recorded on
the SAR images. These result partly from the constraints in imaging
direction that are an inherent feature of SAR imaging and which make the
detection and interpretation of certain objects on an SAR image rather
arbitrary. A further difficulty is the presence of background clutter
on all the Seasat SAR images but which is especially noticeable on the
optically processed images tested. At the present stage of the development
and application of satellite SAR imagery for mapping, the limitations
are centered around shortcomings in the image resolution and
quality rather than the geometric characteristics of the imagery or the
rectification techniques which have been devised and implemented for
mapping purposes.
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