[I didn't get a bounce off of CP the first time] From: "dan@geer.org" <dan@geer.org> | 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