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altitude of nearly 200 miles will be available for civil as well
as military photo interpretation work." Modern day remote sensing
scientists might disagree with the sentence which followed in
which it was asserted that "this photography will permit us to
do little more than discover and evaluate, in crudest terms, the
natural resources in vast and remote areas, but will be of
tremendous value in helping to plan for the economic growth
of underdeveloped countries."
3. Improvements During the Past Quarter Century in Sensor
Platforms and Sensor Systems
All of the attendees at this symposium must surely realize that
modern day space photography permits us to do much more (not
little more, as was predicted in the concluding sentence of the
preceding paragraph) than merely to "discover and evaluate, in
crudest terms, the natural resources in vast and remote areas."
Part of the explanation is found in our having underestimated
the potential advantage that would be given to a photo inter-
preter by the overall "synoptic view" as recorded from an alti-
tude of one hundred miles or more and covering a ground area per
frame of photography that was at least a thousand-fold greater
than that to which he was accustomed. But another part of the
explanation results from our failure, prior to the dawning of
the space age, to perceive the remarkable improvements that would
be made in cameras and other sensor systems. For instance, the
aerial photography of a quarter century ago rarely permitted
more than 25 line pairs per millimeter to be discerned. Since
then, improvements in both the emulsions of photographic films
and the optics of sensor systems have been sufficient to make
quite commonplace a four-fold improvement in such resolution.
Furthermore, serious discussions regarding the potential for
obtaining 40-fold improvements frequently are heard.
There also have been some startling improvements in recent years
in various other kinds of sensor systems, including panoramic
cameras, continuous strip cameras, optical mechanical scanners,
and side-looking airborne radar systems. Each of these systems,
when used individually aboard a spacecraft, is able to provide
certain kinds of information that cannot be obtained from any
of the others. More importantly, when the remote sensing data
that has been acquired by several of these sensor systems is
placed in the hands of a competent image analyst, the "convergence
of evidence" principle can be exploited in respects that hereto-
fore were not feasible, thereby adding greatly to the amount and
accuracy of information derivable from space-acquired remote
sensing data.
4. Improvements During the Past Quarter Century in Capabilities
for the Analysis of Remote Sensing Data.
The techniques and equipment used by humans in the analysis of
remote sensing data were, for the first time, comprehensively
described and illustrated in the Manual of Photographic Inter-
pretation (American Society of Photogrammetry, 1960). Since then,
great advances have been made in developing capabilities for the