superior to those obtained with the affine transformation.
RESULTS OF THE DEVLR DIGITALLY PROCESSED IMAGERY
The accuracy figures obtained after testing this imagery are shown in
Table (5). Close inspection of the figures on this table shows that
for both the control and the check points there is a gradual but
insignificant deterioration in accuracy as the higher order terms are
truncated. The linear conformal transformation gave nearly the same
results as the affine or h-term solutions. It is noted that the results
of the control and check points on this image are more consistent than on
the RAE image.
A noticeable feature of the residual errors on all images is their very
highly systematic nature, though to a lesser extent on the optically
processed images. As will be noted from the vector plots of'Figs. 5 to
12, the majority of these plots point in the cross-track direction of
the image either inwards or outwards. This strongly suggests the effect
of variations in topographic relief on the geometric accuracy of the
images. It is indeed possible to eliminate or reduce the effects of
these relief errors by digital monoplotting techniques using a digital
terrain model (DTM) which could be generated from digitizing topographic
maps of the area (see Ali, 1982). This, however, has not been implemented
in this particular experiment; but has been reported on in another investigation
by the present author (see Ali, 1985).
SUMMARY OF THE GEOMETRIC TESTS AND CONCLUSIONS
(i) Metric imformation with an accuracy standard compatible with
very small scale planimetric mapping can be derived from satellite
SAR imagery using both optical and digital processing techniques.
(ii) Interpretation of features for the purpose of selecting suitable
ground control points was very difficult on all images but in
particular on the optically processed ones. On the two digitally
processed images, the background clutter was such a feature that
positive identification of objects was in many cases impossible
without the consultation of the map.
{1443 The optically processed images supplied by ERIM contain substantial
scale errors. The effects of those errors are largely reduced
when a higher order polynomial is ultilized. In contrast, the
digitally processed images suffer less from those scale errors,
Hence inclusion of higher order terms in the polynomial did not
improve the accuracy significantly.
(iv) Although the two digitally processed images of the test area have
been processed using similar processing techniques, it seems that
the geometric fidelity of the DFVLR image is much superior, as can
be noted from the accuracy figures obtained with this image.
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