10
projects (mainly Latin America), the advent of
satellite side-looking radar (Apollo 17 Mission to
the Moon; decision for Earth orbital satellite
radar in SEASAT) and the continuation of the photo-
grammetric evaluation of radar images, stereomodels,
and radar image blocks.
The development of the U.S. military topo-
graphic radar mapping system has been completed.
The system consists of hard-and software for pro-
duction of differentially rectified radar images
(using radar interferometer data), digital mono-
plotting (radar images and digital height model),
contour plotting, and control network densification
(using the radargrammetric analogy to the photo-
grammetric bundle adjustment). However, the com-
plete system has not yet been put to extensive
tests under near-operational conditions.
Side-looking radar has in its short history
(12 years for real-, 6 years for synthetic aperture)
mainly found applications to reconnaissance type
mapping of vast and remote areas, but not to clas-
sical tasks of mapping and charting. The recon-
naissance projects aim at producing image maps
(mosaics) at scales 1:100 000 and smaller. As a
result, radargrammetric investigations have large-
ly concentrated on the methods and accuracy of
planimetric mapping from single strips and blocks
of radar imagery. Single image mapping accuracies
reacheg up to £20 m with 10 control points per
100 km“; and adjustment of blocks of original radar
image strips produced an accuracy of. *150 m with
15 control points per 100 000 km . Both figures
strongly depend on the density of control points
available.
Stereoradargrammetric analyses have been per-
formed, particularly in the period since 1972, but
only in rather small areas and often not represen-
tative of operational environments. Accuracies
achieved are up to *13 m in height, a result that
could perhaps not hold up outside the laboratory
environment, but that should warrant more atten-
tion for stereo radar than has been given in the
context of reconnaissance type radar mapping
projects.
Radar block adjustment is a field of study that
has not attracted the attention of many research
workers. The comparatively weak geometry of all
dynamic (kinematic) imaging systems does not pre-
sent great promise for control network densifica-
tion based on image blocks. However, in the con-
text of reconnaissance type mapping, of image
mosaicking for mapping of sea and lake ice, and
for future planetary exploration (mapping of planet
Venus), radar block adjustment techniques should
have valuable applications.
8.2 Recommendations:
Recommendations for future work on radargram-
metry should be based on the present trend to view
remote sensing as a tool in which various sensors
are integrated into one coherent system: each sen-
sor is producing only a specific component of data;
but only the integration of all the data from var-
ious sources will allow the maximum benefit to be
obtained from remote sensing. This particularly
will be the case with satellite radar, to be
combined with LANDSAT and similar data. In this
context, the most significant tasks of radargram-
metry are in relating the radar image to other
remote sensing data sources. Solution of these
problems will call for differential rectification
or digital monoplotting, employing perhaps the
techniques of digital image processing.
Application of radar to classical mapping tasks
have limited themselves to reconnaissance type map-
ping of remote areas. It is felt that the radar
images have not been completely used to their full
potential in these projects. It is thus recom-
mended to apply more radargrammetric expertise in
radar mapping projects, so that advantage is taken
of the information potential of stereo radar.
Apart from reconnaissance type mapping, radar
might also have some potential as a tool for map
revision. Particularly the advent of satellite
radar may suggest exploration of the limits and
possibilities of radar for map revision.
Stereo radargrammetric analyses have in the
past not dealt with the rather important relation-
ships that exist between physiological limits to
perceiving and measuring a radar stereo model and
various parameters of the radar configuration and
of the imaged area. Such an analysis, while per-
tinent to stereo radargrammetry, would generate
results of significance far outside the mapping
community.
New mapping tasks which have not existed in
the past but are becoming significant now and can
be solved by radar, address the mapping of sea and
lake ice, and perhaps of cloud covered planetary
surfaces such as Venus. The next few years might
see ice mapping as a major radargrammetric task,
while planetary exploration by radar images is in
the more distant future.
ACKNOWLEDGEMENT
I wish to express my gratitude to Dr. Ch. Elachi, D.
Baker, V. Arriola and E. Abbott for their support
during the preparation of this paper.
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