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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