From: "[email protected]" <[email protected]>
| It may be possible, in the not-so-distant-future, to record
| people in ultra high definition from a mile away, but the
| 'technology' can be rendered rather useless with somthing
| like...this
|
| http://ramitia.files.wordpress.com/2010/02/japan-face-masks.jpg
|
>At this time, it is possible to do facial recognition at 500 meters,
>iris recognition at 50 meters, and heartbeat recognition at 5 meters.
>A newspaper open on a table can be read from orbit.
I strongly doubt the part about reading the newspaper from orbit. I don't
doubt that the pattern of text and pictures on the front page could be
identified from orbit. ('Identifying the difference between Pravda and
Izvestia'.) An approximation I once heard is that a lens or mirror of about
4.5 inch in diameter can resolve an angle of one arc-second. A mirror of the
size of the Hubble Space Telescope (which I assume approximates that of the
typical spy satellite today) is about 20x larger, so the resolution should be
20x better, or 1/20 arc-second. That's 1/(57 degrees per
radian)(3600arcseconds per degree)(20) = 1/4,100,000 radian. From an altitude
of 500 kilometers, that's about 1/8 of a meter, or 120 millimeter. Maybe
that's a pixel-pair, but it's far too large to resolve the text on a newspaper.
The best prospect to improve on this resolution would be to use a
'multiple-mirror-telescope' technology. Light-gathering capability isn't
important in this application; high resolution is. Making a spy-telescope out
of a few different mirrors, held precisely many meters apart, could conceivable
achieve resolutions substantially greater than this.
Jim Bell
