Exploring the Unknown - NASA's History Office

188
OBSERVING THE EARTH FROM SPACE
Table 1*
RESOLUTION OF CLOUDS BY SUNLIGHT
(Image orthicon f/10 camera operated at 20:1; + signal-to-noise ratio
at rates of 40, 10, and 4 exposure frames/sec; and a satellite height of 350 mi)
Minimum Resolvable Surface Dimension
Contrast Aperture 40 Frames/Sec 10 Frames/Sec 4 Frames/Sec
(%) (in.) (ft) (ft) (ft)
100 0.5 200± 100± 64±
1.0 100± 50± 32±
2.0 50± 25± 16±
5.0 20± 10± 6±
25 0.5 800 400± 250±
1.0 400 200± 125±
2.0 200 100± 64±
5.0 80 40± 25±
10 0.5 2,000 1,000 640
1.0 1,000 500 320
2.0 500 250 160
5.0 200 100 64
2.5 0.5 8,000 4,000 2,500
1.0 4,000 2,000 1,250
2.0 2,000 1,000 640
5.0 800 400 250
1 0.5 20,000 10,000 6,400
1.0 10,000 5,000 3,200
2.0 5,000 2,500 1,000
5.0 2,000 1,000 640
* The material contained in this table was prepared by Dr. R. S. Wehner and is included
in RAND Report R-217 (see footnote 1 . . .).
+ It should be noted that this table (and also Tables 2 and 3) is unrealistic in that the
20:1 signal-to-noise ratio is applicable only to 25 per cent contrast. For 10 per cent
contrast, a signal-to-noise ratio of 50:1 is required. This would mean a required transmitter
power increase by a factor of 2.5 (assuming a 2-in. aperture 1000 TV lines, and
a frame frequency of 10 sec). This is still not prohibitive but does become so with a
substantial increase in either the number of TV lines or the frame frequency.
± Values of computed resolution smaller than realizable with present commercial image
orthicons.